university of groningen synthesis of novel branched …...enhanced oil recovery 13 hot water...

University of Groningen

Synthesis of novel branched polymers for enhanced oil recoveryvan Mastrigt, Frank

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Citation for published version (APA):van Mastrigt, F. (2017). Synthesis of novel branched polymers for enhanced oil recovery. [Groningen]:Rijksuniversiteit Groningen.

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Abbreviation DescriptionPEGMA poly(ethylene glycol)methacrylatePF polymer floodPLA polylactic acidPNIPAM poly(N -isopropylacrylamide)ppm parts per millionPV pore volumeRAFT reversible addition-fragmentation chain-transferRI refractive indexRRF residual resistance factorSB-PAM star-like branched polyacrylamideSB-polymer star-like branched polymerSRF shear resistance factorSSS sodium 4-vinylbenzenesulfonateSt styreneTBA tert-butyl acrylateTBAm N -tert-butylacrylamidetBDB tert-butyl dithiobenzoateTBSPNDS potassium 2-(2-thiobenzoylsulfanylpropionylimino)

naphthalene-6,8-disulfonateTCPA 3-(trithiocarbonyl) propanoic acidTHF tetrahydrofuranTPB 1,3-bis(2-(thiobenzoylthio)prop-2-yl)benzeneTSPE sodium 2-(2-thiobenzoylsulfonylpropionylamino)

ethanesulfonateUCST upper critical solution temperatureVA vinyl acetateVB sodium 4-vinylbenzoateVBTA (ar-vinylbenzyl)trimethylammonium chlorideViBCPA 3-((((4-vinylbenzyl)thio)carbonothioyl)thio) propanoic acidVPPS 3-(2-vinylpyridinio)propanesulfonate

1Introduction

Abstract

Polymer flooding, being one of the most widely applied enhanced oil recovery(EOR) techniques, finds application in a wide range of oil fields. The currentlyapplied hydrolysed polyacrylamide (HPAM), however, suffers from some limita-tions. Current research is focussed on overcoming these limitations by altering thetopology and chemical structure of the polymer. For delivering control over themolecular architecture and the reaction, controlled radical polymerisation (CRP)techniques have proven very valuable. The majority of current research considersatom transfer radical polymerisation (ATRP). Reversible addition-fragmentationchain-transfer (RAFT) polymerisation, on the other hand, has high potential be-cause of its versatility and high industrial relevance. Little is known about theapplication of RAFT polymerisation in the synthesis of water soluble polymersfor application in EOR. Therefore, this introduction considers the application ofRAFT polymerisation in the synthesis of water soluble polymers.

9

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10 CHAPTER 1. INTRODUCTION

1.1 Energy

In the last decade, whilst the overall world economy grew, emissions related to en-ergy production and consumption started to decrease for the first time.1 Human-induced global warming, however, impacts the average global temperature of theearth, thereby reaching record high temperatures in recent years.2 General con-sensus dictates that a rigorous approach is required in order to limit the mean risein global temperature to 2 ◦C.3–7 While awareness regarding emissions is increas-ing, continuing the production of petroleum, coal and natural gas is inevitable.8

In figure 1, an overview of the current primary consumption, versus a predictionfor 2030 is displayed. While a relative increase in renewable energy becomes ap-parent, nearly 80% of consumption is in the form of petroleum, coal, and naturalgas, the latter three in equal quantities. While one might argue that, indeed, theshare of petroleum is slightly decreasing, the total primary energy consumptionis projected to increase by 56% between 2010 and 2040.9 More specifically, worldpetroleum (and other liquid fuel) consumption is predicted to increase by 23.7%between 2010 and 2030.10 Even in a very optimistic scenario, with a significantchange in environmental policies around the globe, mankind will be to a high de-gree relying on petroleum in the near future.11

Figure 1: World primary energy consumption in 201412 and 2030 (projection8)

1.2 Oil production

In 2014, global oil production equalled 93 million barrels per day, approaching a20% increase since the year 2000.13 This oil originates from reservoirs, consisting ofpermeable porous rock, in which oil is accumulated. Sandstone is the most commonrock found in oil fields, accounting for approximately 80% of oil reservoirs, followed

1.2. OIL PRODUCTION 11

by carbonates.14 The reservoir is enclosed on the upper face by an impermeablecap. In case of saturation, oil and gas are present as two layers and the toplayer is referred to as the gas cap.15 Water is generally present as a bottom layer,denominated the aquifer, besides a film on the surface of the rock.14,16 Oil recoveryfrom oilfields undergoes three distinct phases before reaching maturity, referred toas the primary, secondary, and tertiary stage.17

1.2.1 Primary recovery

In primary recovery, natural pressure is the driving force behind production (fig-ure 2), as the pressure at the bottom of the well exceeds the hydrostatic pressureexerted by the oil in the well.18 With pressure above the bubble point, productionwill consist predominantly of oil. Falling pressure, however, results in dissolvedgas coming out of solution and dominating production due to its lower viscosity.The latter is accelerated by the increase in viscosity of the oil above the bubblepoint, reducing its mobility. The declining pressure difference between well andatmosphere is backed up by artificial lift techniques, e.g. pumps, and productionis continued until the oil cut (i.e. fraction of oil) at the wellbore reaches uneco-nomically low values. Typical primary recovery factors range from 5 to 15% of theoriginal oil in place (OOIP).19

Figure 2: Primary oil production

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1


1.1 Energy

In the last decade, whilst the overall world economy grew, emissions related to en-ergy production and consumption started to decrease for the first time.1 Human-induced global warming, however, impacts the average global temperature of theearth, thereby reaching record high temperatures in recent years.2 General con-sensus dictates that a rigorous approach is required in order to limit the mean risein global temperature to 2 ◦C.3–7 While awareness regarding emissions is increas-ing, continuing the production of petroleum, coal and natural gas is inevitable.8

In figure 1, an overview of the current primary consumption, versus a predictionfor 2030 is displayed. While a relative increase in renewable energy becomes ap-parent, nearly 80% of consumption is in the form of petroleum, coal, and naturalgas, the latter three in equal quantities. While one might argue that, indeed, theshare of petroleum is slightly decreasing, the total primary energy consumptionis projected to increase by 56% between 2010 and 2040.9 More specifically, worldpetroleum (and other liquid fuel) consumption is predicted to increase by 23.7%between 2010 and 2030.10 Even in a very optimistic scenario, with a significantchange in environmental policies around the globe, mankind will be to a high de-gree relying on petroleum in the near future.11

Figure 1: World primary energy consumption in 201412 and 2030 (projection8)

1.2 Oil production

In 2014, global oil production equalled 93 million barrels per day, approaching a20% increase since the year 2000.13 This oil originates from reservoirs, consisting ofpermeable porous rock, in which oil is accumulated. Sandstone is the most commonrock found in oil fields, accounting for approximately 80% of oil reservoirs, followed

1.2. OIL PRODUCTION 11

by carbonates.14 The reservoir is enclosed on the upper face by an impermeablecap. In case of saturation, oil and gas are present as two layers and the toplayer is referred to as the gas cap.15 Water is generally present as a bottom layer,denominated the aquifer, besides a film on the surface of the rock.14,16 Oil recoveryfrom oilfields undergoes three distinct phases before reaching maturity, referred toas the primary, secondary, and tertiary stage.17

1.2.1 Primary recovery

In primary recovery, natural pressure is the driving force behind production (fig-ure 2), as the pressure at the bottom of the well exceeds the hydrostatic pressureexerted by the oil in the well.18 With pressure above the bubble point, productionwill consist predominantly of oil. Falling pressure, however, results in dissolvedgas coming out of solution and dominating production due to its lower viscosity.The latter is accelerated by the increase in viscosity of the oil above the bubblepoint, reducing its mobility. The declining pressure difference between well andatmosphere is backed up by artificial lift techniques, e.g. pumps, and productionis continued until the oil cut (i.e. fraction of oil) at the wellbore reaches uneco-nomically low values. Typical primary recovery factors range from 5 to 15% of theoriginal oil in place (OOIP).19

Figure 2: Primary oil production

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1.2.2 Secondary recovery

Before reaching the bubble point, generally, the secondary recovery stage is initi-ated. At this stage, reservoir pressure is maintained by injection of pressurised gasat the top of the reservoir, or water in the lower areas of the reservoir, as is schemat-ically illustrated in figure 3. Production is continued until water is produced andthe oil cut becomes uneconomical. Depending on the exact oil field, total recoveryafter the secondary stage is 20 to 40% of the OOIP.20–22 Any technique appliedafter secondary recovery, is referred to as tertiary recovery.

Figure 3: Secondary oil production

1.3 Enhanced oil recovery

According to Lake (1989), enhanced oil recovery (EOR) is the recovery of oil froman oilfield, by injecting materials that are not normally present in the reservoir.23

While EOR is often used mistakenly as a synonym for tertiary recovery, it can beapplied in each stage of oil recovery.17 World proven oil reserves are approximately1.3 trillion barrels , with an annual consumption of nearly 34 billion barrels (2014).Conventional oil reserves total 7 to 8 trillion barrels, which can be partly recov-ered by improved techniques (e.g. EOR).24 Typical recovery potential by EORfor light oils is 45%, however, for heavy oils 90% is reported, and for tar sands100% of the OOIP, resulting from low recoveries during the primary and secondarystages.25 EOR methods can be divided into two groups, thermal and non-thermalones.25 Thermal methods are predominantly applied for heavy oils and tar sands,while non-thermal ones are more suitable for lighter oils. Thermal methods include

1.3. ENHANCED OIL RECOVERY 13

hot water drive,26 steam injection,27–30 in situ combustion,31–33 and electricalheating.34,35 Non-thermal methods range from miscible flooding,36–38 to chemicalflooding,39–43 immiscible flooding,44–46 and other methods such as microbial EORand foam flooding.47–50 Within non-thermal recovery, polymer flooding is the mostwidely applied method,51 with successful applications over the last decades in theUnited States of America, China, Angola, and Oman.49,52–55

1.3.1 Polymer flooding

Because of its effectivity in increasing oil production, its applicability in a widerange of oil fields, and its low cost, water flooding is the most commonly appliedsecondary recovery technique. The effectiveness of water flooding is determinedby both microscopic and macroscopic characteristics. The microscopic efficiencyis a function of interfacial tension, wettability, contact angle, and viscosity. Themacroscopic efficiency depends on the reservoir dimensions, differences in perme-ability within the field, and the mobility ratio. The microscopic efficiency denotesthe capability of water to remove oil from pores, while the macroscopic efficiencyis related to the displacement of (microscopically) mobilised oil to the productionwell.

λ =kiµi

(1.1)

Especially of importance is the mobility ratio (Eq. 1.1), defined as the relativepermeability of a fluid (ki), divided by its viscosity (µi). The water to oil mobilityratio relates the mobility ratio of water to the oil and is calculated by dividing themobility ratio of water by that of the oil in the designated field (Eq. 1.2).

M =kwµw

µo

ko(1.2)

where kw is the relative permeability of water, ko the relative permeability ofoil, µw the viscosity of water, and µo the viscosity of oil.

A mobility ratio ≤ 1 is desirable, as the displacing phase is less mobile thanthe displaced phase, resulting in the displaced oil to move more easily through thereservoir. Because of the low viscosity of water, the water to oil mobility ratiois generally above 1, leading to instabilities in the flow and a phenomenon named‘viscous fingering’ as depicted in figure 4.23 The latter originates from water findingpathways with the least resistance, thereby bypassing the majority of the oil. Thehigh mobility ratio results in a decreasing oil cut and eventually the production ofinjected water.

By decreasing the water to oil mobility ratio, sweep efficiency is improved and apiston like displacement is obtained (figure 5). The mobility ratio can be improved

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1


1.2.2 Secondary recovery

Before reaching the bubble point, generally, the secondary recovery stage is initi-ated. At this stage, reservoir pressure is maintained by injection of pressurised gasat the top of the reservoir, or water in the lower areas of the reservoir, as is schemat-ically illustrated in figure 3. Production is continued until water is produced andthe oil cut becomes uneconomical. Depending on the exact oil field, total recoveryafter the secondary stage is 20 to 40% of the OOIP.20–22 Any technique appliedafter secondary recovery, is referred to as tertiary recovery.

Figure 3: Secondary oil production

1.3 Enhanced oil recovery

According to Lake (1989), enhanced oil recovery (EOR) is the recovery of oil froman oilfield, by injecting materials that are not normally present in the reservoir.23

While EOR is often used mistakenly as a synonym for tertiary recovery, it can beapplied in each stage of oil recovery.17 World proven oil reserves are approximately1.3 trillion barrels , with an annual consumption of nearly 34 billion barrels (2014).Conventional oil reserves total 7 to 8 trillion barrels, which can be partly recov-ered by improved techniques (e.g. EOR).24 Typical recovery potential by EORfor light oils is 45%, however, for heavy oils 90% is reported, and for tar sands100% of the OOIP, resulting from low recoveries during the primary and secondarystages.25 EOR methods can be divided into two groups, thermal and non-thermalones.25 Thermal methods are predominantly applied for heavy oils and tar sands,while non-thermal ones are more suitable for lighter oils. Thermal methods include


hot water drive,26 steam injection,27–30 in situ combustion,31–33 and electricalheating.34,35 Non-thermal methods range from miscible flooding,36–38 to chemicalflooding,39–43 immiscible flooding,44–46 and other methods such as microbial EORand foam flooding.47–50 Within non-thermal recovery, polymer flooding is the mostwidely applied method,51 with successful applications over the last decades in theUnited States of America, China, Angola, and Oman.49,52–55

1.3.1 Polymer flooding

Because of its effectivity in increasing oil production, its applicability in a widerange of oil fields, and its low cost, water flooding is the most commonly appliedsecondary recovery technique. The effectiveness of water flooding is determinedby both microscopic and macroscopic characteristics. The microscopic efficiencyis a function of interfacial tension, wettability, contact angle, and viscosity. Themacroscopic efficiency depends on the reservoir dimensions, differences in perme-ability within the field, and the mobility ratio. The microscopic efficiency denotesthe capability of water to remove oil from pores, while the macroscopic efficiencyis related to the displacement of (microscopically) mobilised oil to the productionwell.

λ =kiµi

(1.1)

Especially of importance is the mobility ratio (Eq. 1.1), defined as the relativepermeability of a fluid (ki), divided by its viscosity (µi). The water to oil mobilityratio relates the mobility ratio of water to the oil and is calculated by dividing themobility ratio of water by that of the oil in the designated field (Eq. 1.2).

M =kwµw

µo

ko(1.2)

where kw is the relative permeability of water, ko the relative permeability ofoil, µw the viscosity of water, and µo the viscosity of oil.

A mobility ratio ≤ 1 is desirable, as the displacing phase is less mobile thanthe displaced phase, resulting in the displaced oil to move more easily through thereservoir. Because of the low viscosity of water, the water to oil mobility ratiois generally above 1, leading to instabilities in the flow and a phenomenon named‘viscous fingering’ as depicted in figure 4.23 The latter originates from water findingpathways with the least resistance, thereby bypassing the majority of the oil. Thehigh mobility ratio results in a decreasing oil cut and eventually the production ofinjected water.

By decreasing the water to oil mobility ratio, sweep efficiency is improved and apiston like displacement is obtained (figure 5). The mobility ratio can be improved

Thesis1.indd 17 29-10-2017 11:02:17


Figure 4: ’Viscous fingering’

by altering the permeability of the porous media, decreasing the viscosity of thedisplaced fluid, or increasing the viscosity of the displacing fluid. While it is possibleto affect the permeability of porous media,56 in commercial applications one of thelatter approaches is applied.

Figure 5: Piston-like displacement

By dissolving a polymer in the injected water, the viscosity of the displac-ing fluid is increased, thereby decreasing the water to oil mobility ratio.53,57 Asa consequence, oil recovery rate is elevated58 and additional oil is produced be-fore breakthrough of the fluid (polymer) at the production well occurs.59 Thelatter implies a lower residual oil saturation after a polymer flood compared witha water flood.60 Residual oil can be present in several forms, depending on thestructure of the oil field. Generally, residual oil is present in dead ends, in gan-glia in pore throats, at corners of pores, and in the form of a film on the surfaceof the walls.61 Ideally, applied polymers are suitable for application in varioustypes of reservoirs. Relevant characteristics of polymers for EOR are tempera-ture resistance, salt resistance, solution stability over a prolonged period (hydrol-


ysis resistance), applicability in low-permeable reservoirs, and suitability over abroad range of oil viscosities.17,23 Currently applied polymers are high molecu-lar weight anionic polymers based on acrylamide,62 or xanthan gum.63 The mostused polymer consists of acrylamide (AM) and acrylic acid (AA) in a ratio of70:30. The latter copolymer, generally referred to as hydrolysed polyacrylamide(HPAM), suffers from high sensitivity to salts and low temperature resistance. Forapplication in reservoirs at more severe conditions, however, copolymers contain-ing 2-acrylamide-2-methylpropanesulfonic acid (AMPS)64 and N -vinylpyrrolidone(NVP)65 are available, as well as the biopolymer xanthan gum.66–68

Polyacrylamide

The viscosifying effect of polyacrylamide (PAM) arises from its very high molecularweight (>107). In order to enhance solution viscosity and facilitate a high rate ofdissolution, acrylid acid (AA) is introduced during synthesis, or a post-hydrolysisstep is performed. This latter polymer, partially hydrolysed polyacrylamide(HPAM, depicted in figure 6), contains randomly distributed negative chargesalong the backbone, leading to stretching of the polymer coil because of elec-trostatic repulsion. Increased repulsion within coils enhances the hydrodynamicvolume of the latter, offering a pronounced increase in solution viscosity.69,70 Thelatter effect is limited by a certain threshold value, occurring at >70% degree ofhydrolysis, referred to as counterion condensation.71 In current practice, between15 and 35% of the monomeric units is negatively charged, affording an optimumbetween solution viscosity and stability of the coils in presence of ions.55 Anincreased ionic strength of the solution, namely, results in increased shielding ofthe repulsion and inversely affects the polymer coil size.72

OH2N O-O

n m

Figure 6: Structure of partially hydrolysed polyacrylamide (HPAM)

Next to the adverse effect of salts on solution viscosity, hardness (presence ofdivalent ions, e.g. Mg2+ and especially Ca2+) limits the applicability of HPAM atelevated temperatures. Based on cloud-point measurements, hardness limits areat 2,000, 500, and 270 mg/L for temperatures of 75, 88, and 96 ◦C respectively.73

At higher concentrations of divalent ions, gel formation or polymer precipitation isobserved, and the solution viscosity is found to decrease.74 At elevated tempera-tures, i.e. those present in reservoirs, hydrolysis progresses, leading to an increasein anionicity of the polymer.75 The latter leads to more pronounced salt sensitiv-

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1


Figure 4: ’Viscous fingering’

by altering the permeability of the porous media, decreasing the viscosity of thedisplaced fluid, or increasing the viscosity of the displacing fluid. While it is possibleto affect the permeability of porous media,56 in commercial applications one of thelatter approaches is applied.

Figure 5: Piston-like displacement

By dissolving a polymer in the injected water, the viscosity of the displac-ing fluid is increased, thereby decreasing the water to oil mobility ratio.53,57 Asa consequence, oil recovery rate is elevated58 and additional oil is produced be-fore breakthrough of the fluid (polymer) at the production well occurs.59 Thelatter implies a lower residual oil saturation after a polymer flood compared witha water flood.60 Residual oil can be present in several forms, depending on thestructure of the oil field. Generally, residual oil is present in dead ends, in gan-glia in pore throats, at corners of pores, and in the form of a film on the surfaceof the walls.61 Ideally, applied polymers are suitable for application in varioustypes of reservoirs. Relevant characteristics of polymers for EOR are tempera-ture resistance, salt resistance, solution stability over a prolonged period (hydrol-


ysis resistance), applicability in low-permeable reservoirs, and suitability over abroad range of oil viscosities.17,23 Currently applied polymers are high molecu-lar weight anionic polymers based on acrylamide,62 or xanthan gum.63 The mostused polymer consists of acrylamide (AM) and acrylic acid (AA) in a ratio of70:30. The latter copolymer, generally referred to as hydrolysed polyacrylamide(HPAM), suffers from high sensitivity to salts and low temperature resistance. Forapplication in reservoirs at more severe conditions, however, copolymers contain-ing 2-acrylamide-2-methylpropanesulfonic acid (AMPS)64 and N -vinylpyrrolidone(NVP)65 are available, as well as the biopolymer xanthan gum.66–68

Polyacrylamide

The viscosifying effect of polyacrylamide (PAM) arises from its very high molecularweight (>107). In order to enhance solution viscosity and facilitate a high rate ofdissolution, acrylid acid (AA) is introduced during synthesis, or a post-hydrolysisstep is performed. This latter polymer, partially hydrolysed polyacrylamide(HPAM, depicted in figure 6), contains randomly distributed negative chargesalong the backbone, leading to stretching of the polymer coil because of elec-trostatic repulsion. Increased repulsion within coils enhances the hydrodynamicvolume of the latter, offering a pronounced increase in solution viscosity.69,70 Thelatter effect is limited by a certain threshold value, occurring at >70% degree ofhydrolysis, referred to as counterion condensation.71 In current practice, between15 and 35% of the monomeric units is negatively charged, affording an optimumbetween solution viscosity and stability of the coils in presence of ions.55 Anincreased ionic strength of the solution, namely, results in increased shielding ofthe repulsion and inversely affects the polymer coil size.72

OH2N O-O

n m

Figure 6: Structure of partially hydrolysed polyacrylamide (HPAM)

Next to the adverse effect of salts on solution viscosity, hardness (presence ofdivalent ions, e.g. Mg2+ and especially Ca2+) limits the applicability of HPAM atelevated temperatures. Based on cloud-point measurements, hardness limits areat 2,000, 500, and 270 mg/L for temperatures of 75, 88, and 96 ◦C respectively.73

At higher concentrations of divalent ions, gel formation or polymer precipitation isobserved, and the solution viscosity is found to decrease.74 At elevated tempera-tures, i.e. those present in reservoirs, hydrolysis progresses, leading to an increasein anionicity of the polymer.75 The latter leads to more pronounced salt sensitiv-

Thesis1.indd 19 29-10-2017 11:02:20


ity and precipitation in presence of lower concentrations of divalent ions.76 Therheology of HPAM solutions in porous media was found to deviate from that mea-sured with a viscometer.77 In porous media, at low velocities, slight shear thinningbehaviour is reported,78 as well as (near) Newtonian behaviour.79 Bulk rheologyfollows the same trend, however, at a certain shear rate bulk viscosity starts todecline, displaying a clear shear thinning trend. The apparent viscosity in porousmedia, on the other hand, starts to increase at average to high flow rates, dis-playing shear thickening behaviour.79–81 At low flow rates, in porous media withlow permeability (55 mD), HPAM displays shear thinning behaviour, attributed tothe presence of very high molecular weight polymer chains. Because of mechanicaldegradation, these chains are not anticipated to penetrate far into the reservoir.82

At higher flow rates, shear thinning in porous media is only observed at low salinityor high polymer concentration. In practice, however, the degree of shear thinningis considered negligible.82 HPAM is relatively resistant to bacterial degradation,83

especially compared with the more rigid and less ionic xanthan gum. The latterpolymer, however, has a high resistance to salts or hardness.84

Xanthan gum

Xanthan gum, an extracellular polysaccharide, is produced by the microorganismXanthomonas campestris amongst others66 and consists of a cellulose backbone,which is substituted with charged side chains containing trisaccharides, renderingthe polymer a polyelectrolyte85 (displayed in figure 7). Contrarily to the vastmajority of polyelectrolytes, xanthan gum does not display a loss in viscosifyingbehaviour in solutions at high ionic strength. The latter effect is ascribed to aconformational change of the polymer, from disordered to ordered, in presence ofsalts.85 Moreover, xanthan gum solutions are known for their viscosity insensitivityto temperature, especially at high salt concentrations.86 Up to temperatures of 80to 90 ◦C and in presence of salts, viscosity of samples was retained to a high degreeover a period of 800 days.87 However, pronounced degradation at temperatures of100 ◦C and above was reported. Aqueous solutions of the polymer were found todisplay properties of pseudoplastic and plastic polymer solutions.86 The viscosi-fying behaviour of xanthan gum stems to a high degree from its high molecularweight. Molecular weights ranging from 2 x 106 to 2 x 107 Da are reported,86,88,89

whereby the higher values might be attributed to association phenomena.90 Be-cause of the high molecular weight of the polymers, dispersities are difficult tomeasure, however, values of 2.25 and 2.8 are reported in literature.91,92

The ordered conformation of xanthan gum is reported to be more shear stablethan its unordered equivalent,85 and is reported to withstand shearing at 5,000 s-1

for 30 min. Furthermore, the conformation has a pronounced effect on the solutionviscosity. Predominantly at low shear rates, higher viscosities are obtained with the


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disordered conformation. At higher shear rates (>3,000 s-1), comparable viscositiesare obtained for both analogues. Compared to HPAM, less data from actual oilfields are available. However, xanthan gum has been applied as viscosifying agentin polymer flooding in some instances over the last decades. Pilot studies in theYumen and Shengli oil fields in China were reported to be successful.63,93

1.3.2 Topology

In order to improve the properties of HPAM, modification of the polymer has beenproposed, referring to alterations of the topology or chemical structure. The mainattention is directed towards rendering the polymer more shear resistant and en-hancing its viscosifying effect, salt tolerance, and temperature resistance.67,94–97

Regarding topology, altering the molecular architectures has been receiving muchattention, whereby structures ranging from comb to block, star and hyperbranchedwere synthesised.98,99 A schematic representation of the latter structures is dis-played in figure 8. From an application point of view, (hyper)branched watersoluble polymers are relevant, as they display unique rheological properties com-pared with linear equivalents, expressed in more predominant elastic behaviour andin some instances a reported higher viscosifying effect.100–102

Recently, branched hydrophobically modified polyacrylamide was synthesisedby free radical polymerisation of a branched core, AM, AA and an hydropho-bic monomer.103 The resulting polymer was found to display higher temperatureand salt resistance than a commercial HPAM equivalent, as well as a more pro-nounced viscosifying behaviour. Furthermore, higher viscoelasticity was reported,attributed to extended relaxation times of deformation induced by the high degreeof branching. Similar results were obtained for comb-shaped hydrolysed acrylamidepolymers, synthesised by free radical polymerisation.104 Comb polymers were found





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-O

O



1.3.2 Topology




Thesis1.indd 21 29-10-2017 11:02:22


A B

C D

Figure 8: Topology of polymers. A: Comb, B: Block, C: Star, D: Hyperbranched

to be more efficient viscosifiers than linear HPAM, especially when the hydropho-bic arms are sufficiently long and hydrophobic interactions afford strong associationbetween polymers. Even at comparable degree of hydrolysis, higher salt resistanceand temperature resistance was reported for the branched equivalents, attributed tosteric hindrance and intermolecular associations. Unfortunately, molecular weightswere not listed and viscoelastic properties of the polymers were not investigated,making the comparison to a commercial polymer at least challenging.

Free radical polymerisation was employed in the synthesis of core-shell hy-perbranched polymers consisting of a core of nano-SiO2, hyperbranched polyami-doamide (PAMAM) as subshell, and linear arms of AM, AA and 2-acrylamide-2-methylpropanesulfonic acid (AMPS).105 Polymers were found to display excellentshear, salt, and temperature resistance, as well as more elastic behaviour comparedwith a linear polymer consisting of AM, AA, and AMPS. Moreover, oil recoveryfrom porous rock was found to be higher than for the linear analogue.

In order to synthesise well defined polymers, traditional methods such asanionic, cationic, and group transfer polymerisations are challenging to implementat industrial scale, as these polymerisations are very sensitive to impurities andreaction conditions.106,107 Free radical polymerisation, on the other hand, failsin delivering sufficient control over the polymeric architecture and uniformity ofthe reaction mixture.108 In contrast to the aforementioned methods, controlledradical polymerisation (CRP) techniques as nitroxide-mediated polymerisation(NMP),109–111 atom transfer radical polymerisation (ATRP),112–114 and reversibleaddition-fragmentation chain transfer (RAFT) polymerisation115–117 offer control


over the architecture of the polymer, as well as its molecular weight distribution.The versatility of CRP techniques has been illustrated by the various polymerarchitectures that have been synthesised over the past decades.118–121

A significant amount of literature is available in which ATRP is employed inthe synthesis of polymers with different structures, e.g. comb polymers for EOR,as reported by Wever et al.122 Linear AM polymers synthesised with ATRP inaqueous medium were compared with star (4-arm) and comb (12-arm) equivalentswith similar number average molecular weights. Comb polymers were found todisplay more pronounced elastic behaviour, compared with their linear and staranalogues, especially at low shear rates (≤ 10 rad s-1). The effect of a hydrophobicblock was studied by synthesising random and diblock branched copolymers with 4,8, or 13 arms with ATRP.123 Block copolymers of AM and N -isopropylacrylamide(NIPAM) were found to precipitate out of solution at temperatures above thelower critical solution temperature (LCST), while random copolymers were foundto stay in solution and display thermothickening behaviour at low shear rates.The effect of the number of arms on the solution rheology of comb polymers hasbeen clearly displayed.124 Intrinsic viscosity of a linear, 4 and 8 arm PAM werefound to be comparable; however, 13 and 17 arm PAM equivalents displayed asignificantly higher viscosity. Based on performance in a two dimensional flow-celland sandstone cores, comb polymers of AM were found to perform comparable toor better than linear PAMs, at lower polymer concentrations.125 Moreover, well-defined diblock, triblock and four arm star amphiphilic block copolymers weresynthesised by ATRP.126 Polymers were found to be very efficient viscosifiers, sol-gel transitions were obtained at very low polymer concentrations (1,000 ppm).Ionic strength and pH were found to be of great influence on the rheology of thepolymer solution, solution viscosity was pronouncedly lowered by decreasing thepH or increasing salt concentration.

Limited research is available in which RAFT polymerisation is applied in thesynthesis of (branched) polymers for EOR. Recently, however, RAFT was em-ployed in the synthesis of polyzwitterions, polymers bearing both cationic andanionic functionalities, that are envisioned for application in EOR.107 In absenceof salts, the latter polymers adopt a collapsed conformation. Upon the addition ofelectrolytes, on the other hand, random coil conformations are reported. Moreover,stimuli responsive block copolymers were successfully synthesised, displaying phaseor conformational change upon a change in solution pH, electrolyte concentration,or temperature. The latter polymers, however, were not evaluated in applicationtests.

To the authors best knowledge, no literature is available describing the ap-plication of NMP in the synthesis of polymers designated for EOR. Since RAFTpolymerisation is conceivably more versatile than NMP and ATRP,127,128 ableto control the polymerisation of a broad range of monomers, the current work


A B

C D











A B

C D










Thesis1.indd 22 29-10-2017 11:02:23

1


A B

C D











A B

C D











A B

C D










Thesis1.indd 23 29-10-2017 11:02:23


emphasises on the application of the former polymerisation technique. Further-more, RAFT polymerisation is compatible with several reaction media, rangingfrom organic solvents, to water, and dispersed systems.129 A major advantage ofthe application of RAFT polymerisation is its industrial relevance, because of theuncomplicated process development. Compared to a regular free radical polymeri-sation, the sole difference lies in the introduction of a RAFT agent. On top ofthat, no transition metals are required for the polymerisation, making workup ofthe reaction mixture more straightforward as compared with ATRP.130

1.4 RAFT polymerisation

RAFT polymerisation was discovered in 1998131 and employs a procedure similarto conventional free radical polymerisation.115 Different from the latter is the in-troduction of a chain transfer (RAFT) agent which mediates the polymerisation bytrapping radically growing chains, making the latter dormant, thus decreasing theaverage concentration of actively propagating chains.132 In figure 9, an exemplaryoverview of the RAFT polymerisation of AM is shown. Polymerisation is initi-ated by the generation of free radicals. These radicals either react with monomerscontaining double bonds, or react reversibly with the RAFT agent, forming anintermediate radical. This intermediate radical can release a reinitiating group,thereby forming a dormant chain connected to the thiocarbonylthio group of theRAFT agent (1 and 2). The released reinitiating group readily polymerises withmonomer, before it reacts with another dormant chain, leading to release of thedormant chain for further polymerisation, thereby settling the main RAFT equilib-rium (3). Another propagating chain reacts again with the dormant chain, forcingthe initial chain to start propagating.133 The latter equilibrium offers control overthe reaction in terms of molecular weight and polydispersity index (PDI), wherebymolecular weight is governed by the ratio between consumed monomer and RAFTagent.134 Some termination might occur, by disproportionation, recombination, orcross-termination of radical chains.135 The extent to which termination happens,however, can be limited by applying appropriate conditions to the polymerisa-tion.136,137

The selection of a suitable RAFT agent highly influences the results of a RAFTpolymerisation and should be tailored to the applied monomers and reaction condi-tions.138,139 The structure of a RAFT agent is determined by its R-group (leavinggroup) and Z-group (activating group) coupled to a thiocarbonylthio group, asillustrated in figure 10 and shown for several RAFT agents in table 1.

1.4. RAFT POLYMERISATION 21

HON

NOH

O CN

CN O

2 I∆

+ AM

Pn

Z

S

S

S

R

HO

CN

O

Degradation

Z

S

S

SHO

CN

O

S

S

S

R

HO

CN

O

+

1

Z

S

S

S

R

Degradation

Z

S

S

S

S

S

S

R

+

+

2 Pn

Pn

Pn

+

+

Z

S

S

S

R

R

Z

S

S

S

R

Z

Degradation

AM

+

Degradation

3 PmS

S

S

R

Pn S

S

S

R

PnPm

S

S

S

R

Pm

+

PmPn + Termination

BCPA

R

Z

R

Z Degradation

R

Z

AM

Pn

AM

Pn BCPA

- N2

I BCPA

+AMPn

+AMPn

+AM Pn

+AM Pn

+

+

+

BCPA

S S

S

OH

O

BCPA

OH

O

R = Z =

Figure 9: Exemplary reaction scheme for RAFT polymerisation of AM with 3-(((benzylthio)carbonothioyl)thio) propanoic acid (BCPA) as RAFT agent and 4,4’-Azobis(4-cyanovaleric acid) (ACVA) as initiator







HON

NOH

O CN

CN O

2 I∆

+ AM

Pn

Z

S

S

S

R

HO

CN

O

Degradation

Z

S

S

SHO

CN

O

S

S

S

R

HO

CN

O

+

1

Z

S

S

S

R

Degradation

Z

S

S

S

S

S

S

R

+

+

2 Pn

Pn

Pn

+

+

Z

S

S

S

R

R

Z

S

S

S

R

Z

Degradation

AM

+

Degradation

3 PmS

S

S

R

Pn S

S

S

R

PnPm

S

S

S

R

Pm

+

PmPn + Termination

BCPA

R

Z

R

Z Degradation

R

Z

AM

Pn

AM

Pn BCPA

- N2

I BCPA

+AMPn

+AMPn

+AM Pn

+AM Pn

+

+

+

BCPA

S S

S

OH

O

BCPA

OH

O

R = Z =








HON

NOH

O CN

CN O

2 I∆

+ AM

Pn

Z

S

S

S

R

HO

CN

O

Degradation

Z

S

S

SHO

CN

O

S

S

S

R

HO

CN

O

+

1

Z

S

S

S

R

Degradation

Z

S

S

S

S

S

S

R

+

+

2 Pn

Pn

Pn

+

+

Z

S

S

S

R

R

Z

S

S

S

R

Z

Degradation

AM

+

Degradation

3 PmS

S

S

R

Pn S

S

S

R

PnPm

S

S

S

R

Pm

+

PmPn + Termination

BCPA

R

Z

R

Z Degradation

R

Z

AM

Pn

AM

Pn BCPA

- N2

I BCPA

+AMPn

+AMPn

+AM Pn

+AM Pn

+

+

+

BCPA

S S

S

OH

O

BCPA

OH

O

R = Z =


Thesis1.indd 24 29-10-2017 11:02:24

1







HON

NOH

O CN

CN O

2 I∆

+ AM

Pn

Z

S

S

S

R

HO

CN

O

Degradation

Z

S

S

SHO

CN

O

S

S

S

R

HO

CN

O

+

1

Z

S

S

S

R

Degradation

Z

S

S

S

S

S

S

R

+

+

2 Pn

Pn

Pn

+

+

Z

S

S

S

R

R

Z

S

S

S

R

Z

Degradation

AM

+

Degradation

3 PmS

S

S

R

Pn S

S

S

R

PnPm

S

S

S

R

Pm

+

PmPn + Termination

BCPA

R

Z

R

Z Degradation

R

Z

AM

Pn

AM

Pn BCPA

- N2

I BCPA

+AMPn

+AMPn

+AM Pn

+AM Pn

+

+

+

BCPA

S S

S

OH

O

BCPA

OH

O

R = Z =








HON

NOH

O CN

CN O

2 I∆

+ AM

Pn

Z

S

S

S

R

HO

CN

O

Degradation

Z

S

S

SHO

CN

O

S

S

S

R

HO

CN

O

+

1

Z

S

S

S

R

Degradation

Z

S

S

S

S

S

S

R

+

+

2 Pn

Pn

Pn

+

+

Z

S

S

S

R

R

Z

S

S

S

R

Z

Degradation

AM

+

Degradation

3 PmS

S

S

R

Pn S

S

S

R

PnPm

S

S

S

R

Pm

+

PmPn + Termination

BCPA

R

Z

R

Z Degradation

R

Z

AM

Pn

AM

Pn BCPA

- N2

I BCPA

+AMPn

+AMPn

+AM Pn

+AM Pn

+

+

+

BCPA

S S

S

OH

O

BCPA

OH

O

R = Z =








HON

NOH

O CN

CN O

2 I∆

+ AM

Pn

Z

S

S

S

R

HO

CN

O

Degradation

Z

S

S

SHO

CN

O

S

S

S

R

HO

CN

O

+

1

Z

S

S

S

R

Degradation

Z

S

S

S

S

S

S

R

+

+

2 Pn

Pn

Pn

+

+

Z

S

S

S

R

R

Z

S

S

S

R

Z

Degradation

AM

+

Degradation

3 PmS

S

S

R

Pn S

S

S

R

PnPm

S

S

S

R

Pm

+

PmPn + Termination

BCPA

R

Z

R

Z Degradation

R

Z

AM

Pn

AM

Pn BCPA

- N2

I BCPA

+AMPn

+AMPn

+AM Pn

+AM Pn

+

+

+

BCPA

S S

S

OH

O

BCPA

OH

O

R = Z =


Thesis1.indd 25 29-10-2017 11:02:25


R

S

Z

SPn +

R

S

Z

S

Pn

Modifies addition-fragmentation rates

Reactive double bond

Leaving group, reinitiaing polymerisationWeak bond

Figure 10: Addition of a radical to the RAFT agent with its characteristic R-group andZ-group, adapted from140 and131

1.4.1 Water soluble polymers by RAFT polymerisation

Several monomers have been reported for the synthesis of water soluble polymers byRAFT polymerisation. An overview of the majority of these monomers is depictedin the supplementary information. Moreover, water soluble polymers are poly-merised with a variety of RAFT agents, ranging from a dithioacetate to xanthatesand several trithiocarbonate structures. The majority of the published reactions,however, involves an aromatic dithioester RAFT agent. An overview of the RAFTagents and monomers the latter have been applied to is depicted in table 1.

Table 1: Overview of applied RAFT agents

CTA Z-group R-group Homopolymers Copolymers

Dithioacetate

CPDA AM106

Aromatic dithioesters

tBDB NAM141–144 NAM&TBAm141 TBAm&NAM141

CDB AM106


Table 1 – continued from previous pageCTA Z-group R-group Homopolymers Copolymers

CPDB N NIPAM145

CTP

N

OH

O

AM106,146 MAM146

PEGMA147 APSP147

MAPSP147 MEABSE147

HPMA148 DMA149

VBTA149 DMAPMAM149

6-O-MAMGlc150

AEMA151 APMA151

SSS134 VBTA134

NIPAM152 MAA153

CTP-PEG-CTP: SSS153

DMAEMA154

AM&MAM146

DMA&DMAPMAM149

VBTA&DMAPMAM149

DMAPMA&DMA149

DMAPMA&VBTA149

NIPAM&BisAM155

AEMA&APMA151 SSS&VB134

VBTA&DMVBA134

NIPAM&PEGDAC&BisAM152

MDB

O

NAM142

CMDBOH

O

NAM142 SSS134

TPB NAM142

TSPE

HN

O

SO-

O-

O-

Na+ AM106,156

MTBSPE

HN

O

SO-

O-

O-

Na+

MAM147

MEABSE147

MAETA147

DMAPMAM147 VPPS134

TBSPNDSHN

O

S

S

O OO-

O-

O

OK+

K+

PEGA147

APSP147

SSS147

AETA147

DMAPAM147

VBTA147 VPPS134

VBTA&DMA147

MTBSMPMN+

OCl-

MEABSE147 VPPS134

ICAVB

N

NH

NIPAM157NIPAM & 1,2-Propandiol-3-methacrylate & 9-Anthryl methylmethacrylate 158

BID

N

NH

NIPAM157

Xanthate

MCEX O

OOAM159,160 AA159

DMA160 NIPAM160

AM&BisAM159

AA&BisAM159

AM&AMPS160

DMA&AMPS160

NIPAM&DMA160


R

S

Z

SPn +

R

S

Z

S

Pn









Dithioacetate

CPDA AM106



CDB AM106



CPDB N NIPAM145

CTP

N

OH

O

AM106,146 MAM146

PEGMA147 APSP147

MAPSP147 MEABSE147

HPMA148 DMA149

VBTA149 DMAPMAM149

6-O-MAMGlc150

AEMA151 APMA151

SSS134 VBTA134

NIPAM152 MAA153

CTP-PEG-CTP: SSS153

DMAEMA154

AM&MAM146

DMA&DMAPMAM149

VBTA&DMAPMAM149

DMAPMA&DMA149

DMAPMA&VBTA149

NIPAM&BisAM155


VBTA&DMVBA134


MDB

O

NAM142

CMDBOH

O

NAM142 SSS134

TPB NAM142

TSPE

HN

O

SO-

O-

O-

Na+ AM106,156

MTBSPE

HN

O

SO-

O-

O-

Na+

MAM147

MEABSE147

MAETA147

DMAPMAM147 VPPS134

TBSPNDSHN

O

S

S

O OO-

O-

O

OK+

K+

PEGA147

APSP147

SSS147

AETA147

DMAPAM147

VBTA147 VPPS134

VBTA&DMA147

MTBSMPMN+

OCl-

MEABSE147 VPPS134

ICAVB

N

NH


BID

N

NH

NIPAM157

Xanthate

MCEX O

OOAM159,160 AA159

DMA160 NIPAM160

AM&BisAM159

AA&BisAM159

AM&AMPS160

DMA&AMPS160

NIPAM&DMA160


R

S

Z

SPn +

R

S

Z

S

Pn









Dithioacetate

CPDA AM106



CDB AM106



CPDB N NIPAM145

CTP

N

OH

O

AM106,146 MAM146

PEGMA147 APSP147

MAPSP147 MEABSE147

HPMA148 DMA149

VBTA149 DMAPMAM149

6-O-MAMGlc150

AEMA151 APMA151

SSS134 VBTA134

NIPAM152 MAA153

CTP-PEG-CTP: SSS153

DMAEMA154

AM&MAM146

DMA&DMAPMAM149

VBTA&DMAPMAM149

DMAPMA&DMA149

DMAPMA&VBTA149

NIPAM&BisAM155


VBTA&DMVBA134


MDB

O

NAM142

CMDBOH

O

NAM142 SSS134

TPB NAM142

TSPE

HN

O

SO-

O-

O-

Na+ AM106,156

MTBSPE

HN

O

SO-

O-

O-

Na+

MAM147

MEABSE147

MAETA147

DMAPMAM147 VPPS134

TBSPNDSHN

O

S

S

O OO-

O-

O

OK+

K+

PEGA147

APSP147

SSS147

AETA147

DMAPAM147

VBTA147 VPPS134

VBTA&DMA147

MTBSMPMN+

OCl-

MEABSE147 VPPS134

ICAVB

N

NH


BID

N

NH

NIPAM157

Xanthate

MCEX O

OOAM159,160 AA159

DMA160 NIPAM160

AM&BisAM159

AA&BisAM159

AM&AMPS160

DMA&AMPS160

NIPAM&DMA160

Thesis1.indd 26 29-10-2017 11:02:27

1


R

S

Z

SPn +

R

S

Z

S

Pn









Dithioacetate

CPDA AM106



CDB AM106



CPDB N NIPAM145

CTP

N

OH

O

AM106,146 MAM146

PEGMA147 APSP147

MAPSP147 MEABSE147

HPMA148 DMA149

VBTA149 DMAPMAM149

6-O-MAMGlc150

AEMA151 APMA151

SSS134 VBTA134

NIPAM152 MAA153

CTP-PEG-CTP: SSS153

DMAEMA154

AM&MAM146

DMA&DMAPMAM149

VBTA&DMAPMAM149

DMAPMA&DMA149

DMAPMA&VBTA149

NIPAM&BisAM155


VBTA&DMVBA134


MDB

O

NAM142

CMDBOH

O

NAM142 SSS134

TPB NAM142

TSPE

HN

O

SO-

O-

O-

Na+ AM106,156

MTBSPE

HN

O

SO-

O-

O-

Na+

MAM147

MEABSE147

MAETA147

DMAPMAM147 VPPS134

TBSPNDSHN

O

S

S

O OO-

O-

O

OK+

K+

PEGA147

APSP147

SSS147

AETA147

DMAPAM147

VBTA147 VPPS134

VBTA&DMA147

MTBSMPMN+

OCl-

MEABSE147 VPPS134

ICAVB

N

NH


BID

N

NH

NIPAM157

Xanthate

MCEX O

OOAM159,160 AA159

DMA160 NIPAM160

AM&BisAM159

AA&BisAM159

AM&AMPS160

DMA&AMPS160

NIPAM&DMA160


R

S

Z

SPn +

R

S

Z

S

Pn









Dithioacetate

CPDA AM106



CDB AM106



CPDB N NIPAM145

CTP

N

OH

O

AM106,146 MAM146

PEGMA147 APSP147

MAPSP147 MEABSE147

HPMA148 DMA149

VBTA149 DMAPMAM149

6-O-MAMGlc150

AEMA151 APMA151

SSS134 VBTA134

NIPAM152 MAA153

CTP-PEG-CTP: SSS153

DMAEMA154

AM&MAM146

DMA&DMAPMAM149

VBTA&DMAPMAM149

DMAPMA&DMA149

DMAPMA&VBTA149

NIPAM&BisAM155


VBTA&DMVBA134


MDB

O

NAM142

CMDBOH

O

NAM142 SSS134

TPB NAM142

TSPE

HN

O

SO-

O-

O-

Na+ AM106,156

MTBSPE

HN

O

SO-

O-

O-

Na+

MAM147

MEABSE147

MAETA147

DMAPMAM147 VPPS134

TBSPNDSHN

O

S

S

O OO-

O-

O

OK+

K+

PEGA147

APSP147

SSS147

AETA147

DMAPAM147

VBTA147 VPPS134

VBTA&DMA147

MTBSMPMN+

OCl-

MEABSE147 VPPS134

ICAVB

N

NH


BID

N

NH

NIPAM157

Xanthate

MCEX O

OOAM159,160 AA159

DMA160 NIPAM160

AM&BisAM159

AA&BisAM159

AM&AMPS160

DMA&AMPS160

NIPAM&DMA160


R

S

Z

SPn +

R

S

Z

S

Pn









Dithioacetate

CPDA AM106



CDB AM106



CPDB N NIPAM145

CTP

N

OH

O

AM106,146 MAM146

PEGMA147 APSP147

MAPSP147 MEABSE147

HPMA148 DMA149

VBTA149 DMAPMAM149

6-O-MAMGlc150

AEMA151 APMA151

SSS134 VBTA134

NIPAM152 MAA153

CTP-PEG-CTP: SSS153

DMAEMA154

AM&MAM146

DMA&DMAPMAM149

VBTA&DMAPMAM149

DMAPMA&DMA149

DMAPMA&VBTA149

NIPAM&BisAM155


VBTA&DMVBA134


MDB

O

NAM142

CMDBOH

O

NAM142 SSS134

TPB NAM142

TSPE

HN

O

SO-

O-

O-

Na+ AM106,156

MTBSPE

HN

O

SO-

O-

O-

Na+

MAM147

MEABSE147

MAETA147

DMAPMAM147 VPPS134

TBSPNDSHN

O

S

S

O OO-

O-

O

OK+

K+

PEGA147

APSP147

SSS147

AETA147

DMAPAM147

VBTA147 VPPS134

VBTA&DMA147

MTBSMPMN+

OCl-

MEABSE147 VPPS134

ICAVB

N

NH


BID

N

NH

NIPAM157

Xanthate

MCEX O

OOAM159,160 AA159

DMA160 NIPAM160

AM&BisAM159

AA&BisAM159

AM&AMPS160

DMA&AMPS160

NIPAM&DMA160

Thesis1.indd 27 29-10-2017 11:02:28



Trithiocarbonates

CSTPASHO

O

OH

O

AM161

EMP SOH

O

NIPAM162 DMA163 NIPAM&DMA162

DBTTCS

AM164

BCPASHO

O AM154,165,166 AA154

HEA154 NIPAM154

AMPS154 PEGMA167

AA&AM154 AA&NIPAM154

AA&DMA154 NIPAM&DMA154

PEGMA&DMA154 PEGMA&AA154

AM&BisAM165,166

PEGMA&BisAM167

TCPA HSOH

O

NIPAM&BisAM155

DMP11S OH

ONIPAM168,169 DMA163

Modified with PEG:DMA170 NIPAM170

NIPAM&TBA168

Modified with PEG:DMA&NIPAM170 NIPAM&DMA170

BDAT SHO

O

OH

OAM106,154,171

DMA163,170,171

AA154 HEA154

NIPAM154,162,169,170,172

AMPS154

AA&DMA106 NIPAM&DMA162,170

CEP SO

OH

DMA163

CTPPA S

N

OH

O

MAA173 MAA&PEGMA174–176

Acrylamides and Methacrylamides

For polymerisation of acrylamide (AM), dithioacetate CPDA (structures corre-sponding with abbreviations are depicted in table 1) was employed, as well as aro-matic dithioester agents CDB, CTP, and TSPE. While it was possible to polymeriseup to a molecular weight of 100,000 Da with PDIs below 1.40, the best control wasoffered when a xanthate (MCEX159,160) or trithiocarbonate RAFT agent was ap-plied.106 Trithiocarbonate DBTTC has proven to be an efficient transfer agent inmethanol, effectively mediating the polymerisation under UV-irradiation up to amolecular weight of 50,000 Da with dispersities as low as 1.20.166 Gamma radiationwas employed in the polymerisation of AM in water with BDAT and water/acetonewith BCPA up to molecular weights of 17,000 and 37,000 Da respectively, whilemaintaining low polydispersities.167 Low temperature polymerisation was explored


with redox initiation of AM at 25 to 45 ◦C in presence of trithiocarbonate BDAT.The polymers had molecular weights in good correspondence with their theoreticalvalues, up to 13,400 Da with PDIs up to 1.31. Low temperature polymerisation wasalso reported up to higher molecular weights. A xanthate (MCEX) was modifiedwith AM in a mixture of ethanol and water up to a molecular weight of 650 andsubsequently applied in the polymerisation of additional AM in water, initiated byredox initiation at ambient temperature.160 Molecular weights of almost 1,000,000Da were reached with a claimed polydispersity of 1.12.

Significantly less attention has been devoted to the RAFT polymerisation ofmethacrylamide (MAM). In an aqueous buffer (pH = 5.3), dithiobenzoate CTP wasemployed to polymerise MAM up to a molecular weight of 34,500 Da, with PDIsas low as 1.10.146 The polymer was successfully chain extended with AM. Slightlyhigher molecular weights were obtained with dithiobenzoate MTBSPE in water(pH = 3.0).147 MAM was polymerised up to a molecular weight of approximately60,000 Da, with PDI values below 1.40.

In the polymerisation of N,N -dimethylacrylamide (DMA), generally trithiocar-bonate RAFT agents are employed, whereby water is applied as solvent. In 2010,four different trithiocarbonate structures with different water solubilities were ap-plied in the aqueous polymerisation of DMA as well as in the inverse emulsionpolymerisation in a mixture of water and hexane.163 Molecular weights obtainedin water with BDAT, EMP, and CMP ranged from 35,700 to 42,100 Da and werein good correspondence with theoretical values. Reported PDIs were 1.14, 1.06,and 1.09 respectively. In the inverse microemulsion, less control over the reactionwas observed and molecular weights for BDAT, EMP, CMP, and DMP increasedto 40,000 Da, 69,600, 138,100, and 399,300 Da respectively, at a similar monomerto RAFT agent ratio. The loss of control was also illustrated by the increase inPDI values of 1.68, 1.20, 1.36, and 2.46 respectively. This loss was attributed topartitioning of the RAFT agent into the organic phase. In water, dithiobenzoateCTP was employed to polymerise DMA up to a molecular weight of 8,200 Da (PDI:1.08).149 The polymer was successfully chain extended with DMA up to a molecularweight of 26,700 Da with a PDI of 1.07. Chain extension with DMAPMAM, on theother hand, yielded a very high molecular weight polymer, which was attributed toloss of control of the reaction. Trithiocarbonate DMP was modified with polyethy-lene glycol (PEG) to enhance its water solubility and successively applied to thepolymerisation of DMA at −15 ◦C, yielding molecular weights up to 37,300 Dawith PDIs below 1.25.170 A successful chain extension with N -isopropylacrylamide(NIPAM) was performed, yielding a copolymer with a molecular weight of 62,500Da and a PDI of 1.26. The popular trithiocarbonate BDAT has been employed atlow temperatures in water171 and an aqueous buffer with a pH of approximately5.170 At room temperature, molecular weights up to 78,000 Da were obtained,with PDIs as low as 1.05. At −15 ◦C, the highest molecular weight attained was



Trithiocarbonates

CSTPASHO

O

OH

O

AM161

EMP SOH

O


DBTTCS

AM164

BCPASHO

O AM154,165,166 AA154

HEA154 NIPAM154

AMPS154 PEGMA167




AM&BisAM165,166

PEGMA&BisAM167

TCPA HSOH

O

NIPAM&BisAM155

DMP11S OH



NIPAM&TBA168


BDAT SHO

O

OH

OAM106,154,171

DMA163,170,171

AA154 HEA154

NIPAM154,162,169,170,172

AMPS154


CEP SO

OH

DMA163

CTPPA S

N

OH

O










Trithiocarbonates

CSTPASHO

O

OH

O

AM161

EMP SOH

O


DBTTCS

AM164

BCPASHO

O AM154,165,166 AA154

HEA154 NIPAM154

AMPS154 PEGMA167




AM&BisAM165,166

PEGMA&BisAM167

TCPA HSOH

O

NIPAM&BisAM155

DMP11S OH



NIPAM&TBA168


BDAT SHO

O

OH

OAM106,154,171

DMA163,170,171

AA154 HEA154

NIPAM154,162,169,170,172

AMPS154


CEP SO

OH

DMA163

CTPPA S

N

OH

O








Thesis1.indd 28 29-10-2017 11:02:30

1



Trithiocarbonates

CSTPASHO

O

OH

O

AM161

EMP SOH

O


DBTTCS

AM164

BCPASHO

O AM154,165,166 AA154

HEA154 NIPAM154

AMPS154 PEGMA167




AM&BisAM165,166

PEGMA&BisAM167

TCPA HSOH

O

NIPAM&BisAM155

DMP11S OH



NIPAM&TBA168


BDAT SHO

O

OH

OAM106,154,171

DMA163,170,171

AA154 HEA154

NIPAM154,162,169,170,172

AMPS154


CEP SO

OH

DMA163

CTPPA S

N

OH

O










Trithiocarbonates

CSTPASHO

O

OH

O

AM161

EMP SOH

O


DBTTCS

AM164

BCPASHO

O AM154,165,166 AA154

HEA154 NIPAM154

AMPS154 PEGMA167




AM&BisAM165,166

PEGMA&BisAM167

TCPA HSOH

O

NIPAM&BisAM155

DMP11S OH



NIPAM&TBA168


BDAT SHO

O

OH

OAM106,154,171

DMA163,170,171

AA154 HEA154

NIPAM154,162,169,170,172

AMPS154


CEP SO

OH

DMA163

CTPPA S

N

OH

O










Trithiocarbonates

CSTPASHO

O

OH

O

AM161

EMP SOH

O


DBTTCS

AM164

BCPASHO

O AM154,165,166 AA154

HEA154 NIPAM154

AMPS154 PEGMA167




AM&BisAM165,166

PEGMA&BisAM167

TCPA HSOH

O

NIPAM&BisAM155

DMP11S OH



NIPAM&TBA168


BDAT SHO

O

OH

OAM106,154,171

DMA163,170,171

AA154 HEA154

NIPAM154,162,169,170,172

AMPS154


CEP SO

OH

DMA163

CTPPA S

N

OH

O








Thesis1.indd 29 29-10-2017 11:02:31


30,900 Da, with a PDI of 1.25. In a chain extension experiment with NIPAM, ther-moresponsive copolymers with a molecular weight of 62,500 Da and a PDI of 1.26were obtained. Significantly higher molecular weights were only reported with xan-thate MCEX.160 The xanthate was modified with DMA in ethyl acetate (molecularweight: 1,050 Da) or NIPAM in water (13,000 Da, PDI: 1.28) and extended withDMA in water at room temperature. After polymerisation, initiated by redox,molecular weights of 826,000 and 1,021,000 Da were obtained respectively, withPDI values of 1.11 and 1.51.

In the polymerisation of NIPAM, both dithiobenzoates and trithiocarbonatesare employed. NIPAM was polymerised in DMF in presence of dithiobenzoateCPDB up to a molecular weight of 31,100 Da, with a PDI of 1.27.145 The poly-mer was modified to introduce RAFT groups along the backbone and applied inthe polymerisation of VA or N -vinyl-2-pyrrolidone (NVP) to yield comb-polymers.Moreover, dithiobenzoate CTP was employed in the polymerisation in dioxane,152

yielding thermoresponsive polymers with a molecular weight of 12,000 Da and aPDI of 1.30.

NIPAM was copolymerised with 1,2-propandiol-3-methacrylate and 9-anthrylmethyl methacrylate in dioxane.158 The cloud points of the fluorescent copolymerswere investigated and found to range from 30 to 37 ◦C, depending on the com-position. Unfortunately, molecular weights and polydispersities were not listed.Monomer VBC was polymerised with NIPAM and subsequently modified with 4(5)-Imidazole dithiocarboxylic acid to synthesise a backbone with RAFT groups.177

The Z-group of the dithiobenzoate RAFT agent is identical to that of RAFT agentBID. After polymerisation in DMF, comb polymers with peak molecular weightsbetween 755,000 and 2,795,000 Da and corresponding PDI values from 3.11 to 10.34were obtained. Unmodified BID was applied in the polymerisation of NIPAM indioxane up to a molecular weight of 69,200 Da, with PDIs listed below 1.43.157

Trithiocarbonate DMP was modified with PEG to enhance its water solubility andsuccessively applied in the polymerisation of NIPAM at −15 ◦C up to a molecularweight of 37,300 Da with PDIs below 1.25.170 Subsequent chain extension withDMA yielded a copolymer with a molecular weight of 53,100 Da and a PDI of 1.22.DMP was also applied in the polymerisation of NIPAM in DMF, initiated radicallyor by photo initiation.169 Molecular weights up to 17,500 Da were reported, alongwith PDIs below 1.35. Using DMSO as solvent, a molecular weight of 7,000 Dawas obtained, with a PDI of 1.15.168 A chain extension experiment was performedwith tert-butyl acrylate (TBA), yielding an amphiphilic polymer with a molecularweight of 15,700 Da and a PDI of 1.11. BCPA was employed as RAFT agent inthe polymerisation of NIPAM in water with 15 vol% acetone.154 Polymerisationwas initiated by gamma radiation, yielding a molecular weight of 105,000 Da, witha PDI of 1.12.

The most commonly applied trithiocarbonate, BDAT, has been reported in


several polymerisations of NIPAM.154,162,169,170,172 Both radical and photo initia-tion have been employed in DMF, yielding PNIPAM with molecular weights up to17,500 Da and PDIs up to 1.45.168 Slightly higher molecular weights were affordedby redox initiation in distilled water. Values up to 40,700 Da were reported, withPDI values as low as 1.20.172 By applying gamma radiation in water, molecularweights up to 74,000 Da with low polydispersity (1.10) were obtained.170 Moreover,polymerisation at lower temperature was proven to be viable. At -15, BDAT wasemployed in the polymerisation of NIPAM in an aqueous buffer (pH = 5.0) up to amolecular weight of 33,500 Da with PDIs as low as 1.19.162 Chain extension withDMA yielded a block copolymer with a molecular weight of 65,600 Da and a PDI of1.27. Trithiocarbonate BDAT was compared with EMP, the latter containing a dif-ferent Z-group, leading to polymerisation on one side of the RAFT agent solely.162

PNIPAM with molecular weights up to approximately 75,000 Da were obtained forboth RAFT agents, with PDIs below 1.10. Polymers were chain extended withDMA to yield AB (EMP) or ABA (BDAT) block copolymers. AB block copoly-mers had listed molecular weights up to 61,900 Da with PDIs up to 1.21. The ABAblock copolymers had molecular weights up to 53,000 Da and PDI values below1.15. The polymers are forming reversible micelles upon heating, whereby tran-sition temperature and micelle size depend on the polymer architecture and theNIPAM block length. Star polymers consisting of NIPAM were synthesised withmacro RAFT agents having four actives sites, containing trithiocarbonate groupsand a R-group and Z-group similar to DMP.178 Two different macro RAFT agents,with molecular weights of 9,000 Da and 21,000 Da, where applied in dioxane. Thefinal star polymers had reported molecular weights up to 42,000 Da and PDI valuesranging from 1.05 to 1.15.

N -acryloylmorpholine (NAM) was polymerised with several dithiobenzoateRAFT agents. tBDB was employed in multiple instances, using dioxane assolvent.141–144 Molecular weights ranged from 10,000 Da (PDI < 1.15),143 to40,500 Da (PDI: 1.03),141 up to 80,000 Da with PDI as low as 1.15144 or 1.16142

respectively. A successful chain extension experiment with N -tert-butylacrylamide(TBAm) illustrated the living character of the polymerisation.141 A PNAMhomopolymer (molecular weight: 40,500 Da, PDI: 1.03) was employed in furtherpolymerisation, yielding an amphiphilic copolymer with a molecular weight upto 50,000 Da ( PDI up to 1.25). MDB was employed in the polymerisation ofNAM up to a molecular weight of 40,000 Da, with PDI values up to 1.10.142

Similar PDIs were obtained, in the polymerisation with RAFT agent TPB, upto molecular weights of 70,000 Da. With CMDB, a molecular weight of 75,000Da was reached, while maintaining polydispersities between 1.10 and 1.20.142

N -(2-aminoethyl)acrylamide (AEMA) was polymerised with dithiobenzoate CTPin water:dioxane (2:1 vol/vol).151 Polymers with molecular weights up to 22,700Da were obtained, with polydispersities below 1.20. A macro RAFT agent with a































Thesis1.indd 30 29-10-2017 11:02:32

1














































Thesis1.indd 31 29-10-2017 11:02:32


molecular weight of 8,600 Da (PDI: 1.20) was subjected to chain extension experi-ments with either AEMA, or N -(3-aminopropyl)acrylamide (APMA). After chainextension, molecular weights of 25,300 and 20,500 Da respectively were obtainedwith PDIs of 2.14 and 1.29. APMA was also subjected to homopolymerisations inwater:dioxane (2:1 vol/vol) with CTP up to molecular weights of 26,500 Da andPDI values up to 1.31.151

N -(2-hydroxypropyl)methacrylamide (HPMA) was polymerised withdithiobenzoate CTP in an aqueous buffer (pH = 5.2), up to molecular weights of97,000 Da, while the polydispersity remained below 1.09.148 CTP was employedin the polymerisation N -(3-(dimethylamino)propyl) acrylamide (DMAPAM) aswell.147 In aqueous KCl (pH = 3.2), molecular weights up to 80,000 Da and PDIvalues of approximately 1.20 by multiangle laser light scattering (MALLS) and1.50 by ASEC were stated. 2-acrylamido-2-methylpropanesulfonic acid (AMPS)was polymerised with trithiocarbonate RAFT agents and xanthate MCEX.The latter was modified with AM and AMPS (3:1 mol/mol) in a mixture ofethanol and water160 up to a molecular weight of 700. The macro RAFT agentwas employed in the redox copolymerisation of AM and AMPS, in a similarratio to the macro RAFT agent, yielding a polymer with a molecular weight of1,170,000 Da and a PDI of 1.36. AMPS was also copolymerised with DMA (1:10mol/mol) by redox initiation with a macro RAFT agent of MCEX polymerisedwith DMA (molecular weight: 1,050 Da). A molecular weight of 1,110,000 Daand a PDI of 1.61 were reported for the latter copolymer.160 Other reportedpolymerisations at ambient temperature employed gamma radiation for thepolymerisation with trithiocarbonate BDAT in water, or BCPA in a mixture ofwater and acetone.154 Two dithiobenzoate RAFT agents have been reported in thepolymerisation of N -(3-(dimethylamino)propyl) methacrylamide (DMAPMAM).MTBSPE was employed in water (pH = 4.0), leading to PDMAPMAM polymerswith molecular weights up to approximately 40,000 Da and PDI values below 1.40based on end-group analysis, or below 1.50 based on ASEC.147 Higher molecularweights were obtained with CTP in water, however, control was lost.149 In anaqueous buffer, control was maintained and DMAPMAM was polymerised up toa molecular weight of 40,000 Da with a PDI up to 1.10. A PDMAPMAM macroRAFT agent (molecular weight: 8,700 Da and PDI of 1.08) was extended withDMA, (ar-vinylbenzyl)trimethylammonium chloride (VBTA), or DMAPMAM.The copolymers had reported molecular weights of 37,200, 24,600, and 58,900 Darespectively, with polydispersities of 1.14, 1.11, and 1.12.

Branching in AM polymers was introduced by copolymerising with N,N ’-methylenebisacrylamide (BisAM), a bifunctional AM monomer159,165,166 (depictedin figure 11). Xanthate MCEX was employed in a mixture of water and 2-propanol,yielding branched copolymers of AM and BisAM with a molecular weight upto 7,370, and PDI values ranging from 2.68 to 11.9. Higher molecular weights,


O

HN

HN

O

Figure 11: N,N ’-methylenebisacrylamide (BisAM)

ranging from 560,000 to 1,280,000 Da were obtained when BCPA was used asRAFT agent in an aqueous buffer.165 GPC traces displayed bimodal peaks,resulting in polydispersities ranging from 4.7 to 8.6. Next, the feeding policy ofBisAM was explored.166 By polymerising the arms, before the addition of BisAM,star-shaped polymers with molecular weights up to 715,000 Da and PDIs rangingfrom 1.1 to 2.2 were obtained. In a second approach, the core was first synthesisedby reaction of BisAM with the RAFT agent, followed by the addition of AM inorder to grow arms from the core. The latter approach yielded polymers withmolecular weights up to 579,000 Da and polydispersities between 1.6 and 2.4. In abatch approach, AM was directly copolymerised with BisAM. Molecular weightswere limited to 204,000 Da (PDI: 1.9), at higher BisAM concentration gelationwas observed. With a continuous feeding approach of BisAM, molecular weightsup to 1,290,000 Da with polydispersities from 1.4 to 9.4 were obtained. Moreover,dithiobenzoate CTP was employed in the polymerisation in dioxane.152,155 Theformer yielded thermoresponsive polymers with a molecular weight of 12,000 Daand a PDI of 1.30. The polymer was subsequently crosslinked with BisAM andPEGDAC (vide infra). When solely BisAM was applied in the crosslinking, astar-shaped polymer was obtained with a molecular weight of 25,000 Da and aPDI of 1.70. The latter approach, however, introduced BisAM in the polymerisa-tion. For experiments involving both BisAM and PEGDAC, gel structures werereported. Molecular weights for the latter polymers, were not expressed. Usingtrithiocarbonate TCPA as RAFT agent, NIPAM was copolymerised with BisAMto synthesise a branched macro RAFT agent.155 The latter was chain extendedwith a fresh batch of NIPAM to form a hydrogel. Unfortunately, the authorsdid not mention the molecular weight of the polymers. Ditbiobenzoate ICAVB,bearing a pendant double bond, was applied in the polymerisation of NIPAMin dioxane.157 Molecular weights of the branched polymer up to 61,300 Da werelisted, however, polydispersities were not mentioned.

Acrylates

Trithiocarbonate BDAT was employed in the polymerisation of Acrylic acid (AA)in water, initiated by gamma radiation.154 With this controlled reaction, a polymerwith a molecular weight of 98,000 Da and a PDI of 1.10 was obtained. By applyingtrithiocarbonate BCPA in a mixture of water and acetone, molecular weights up to






O

HN

HN

O



Acrylates







O

HN

HN

O



Acrylates


Thesis1.indd 32 29-10-2017 11:02:33

1






O

HN

HN

O



Acrylates







O

HN

HN

O



Acrylates







O

HN

HN

O



Acrylates


Thesis1.indd 33 29-10-2017 11:02:34


O

OO

O

n

Figure 12: Poly(ethylene glycol) diacrylate (PEGDAC)

230,000 Da were obtained with PDI values below 1.27. Poly(ethyleneglycol) acry-late (PEGA) was polymerised with dithiobenzoate TBSPNDS in aqueous KCl.147

Molecular weights up to 70,000 Da were reported, while the PDI remained below1.40. Acrylate 2-hydroxyethyl acrylate (HEA) was polymerised with two differenttrithiocarbonate RAFT agents, initiated by gamma radiation.154 Polymerisationwith BDAT in water yielded a polymer a molecular weight of 72,000 Da and aPDI of 1.15. When BCPA was employed in a mixture of water and acetone, amolecular weight of 50,000 Da was obtained, with a corresponding PDI of 1.12.2-acryloyloxyethyl trimethyl ammonium (AETA) was polymerised with dithioben-zoate TBSPNDS in aqueous KCl, up to a molecular weight of 80,000 Da and a PDIof approximately 1.35.147 The latter RAFT agent was also employed in the poly-merisation of 3-(acryloyloxy) propanesulfonate potassium salt (APSP).147 WithTBSPNDS as well as CTP, molecular weights up to 100,000 Da were obtained,with PDIs below 1.10. However, with both RAFT agents some high molecularweight polymer was formed, attributed to competition with free radical polymeri-sation.

AA was polymerised in ethanol up to a molecular weight of 2,500 Da (PDI below1.20) with xanthate MCEX.159 Under similar conditions, AA was copolymerisedwith BisAM, yielding branched polymers with molecular weights up to 5,700 Dawith PDI values ranging from 1.25 to 4.27.

Methacrylates

For the polymerisation of methacrylic acid (MAA), both a ditbiobenzoate and atrithiocarbonate RAFT agent have been reported. The former (CTP) was appliedin water, whereby molecular weights up to 15,600 Da were obtained with a low PDIvalue of 1.14.153 The trithiocarbonate CTPPA was employed in the polymerisationof MAA in water, methanol, and dioxane.173 Water offered the highest degree ofcontrol over the polymerisation, as well as favourable kinetics. At a pH of 4 orlower, low polydispersities were obtained (up to 1.27), while molecular weightsof 92,000 Da were reached. At higher pH, control over the reaction was lost.CTTPA was also applied in the preparation of a macro RAFT agent containingMAA and poly(ethylene glycol) methacrylate (PEGMA) (50:50 mol/mol) up to amolecular weight of 16,000 Da.174 The macro RAFT agent was employed in the


emulsion polymerisation of methyl methacrylate (MMA), or MMA with styrene(St). The former polymers had molecular weights ranging from 43,100 to 187,000Da, the latter 51,800 to 54,800 Da, with PDI values of 1.20 to 1.52 and 1.19 to1.14 respectively. Morphology of the copolymers changed from spherical micelles,to fibers, and to vesicles with increasing hydrophobic block size, independent ofthe pH of the aqueous phase. Similar macro RAFT agents, containing MAA andPEGMA in a ratio of 50:50 and 33:66 were synthesised with molecular weights from20,000 to 24,00 Da0.175,176 These macro RAFT agents, with reported PDIs from1.09 to 1.14, were chain extended with St up to a molecular weight of 117,200 Da(PDI up to 1.42), or with MMA. Molecular weights of the latter copolymers wereunfortunately not listed.

Apart from being incorporated into a macro RAFT agent, PEGMA was alsoemployed in the synthesis of homopolymers. Ditbiobenzoate CTP was appliedas RAFT agent in water and polymerisation was initiated by gamma radiation.Molecular weights ranged up to 50,000 Da, with low PDI values as low as 1.07.154

Another study reported molecular weights up to 56,000 Da, again with low poly-dispersities.147 Interestingly, polymers were reported to have a cloud point around83 ◦C.

Other reported polymerisations of methacrylates involved ditiobenzoate RAFTagents. CTP was employed in the polymerisation of N,N -dimethylaminoethylmethacrylate (DMAEMA), 3-(methacryloyloxy) propanesulfonate potassium salt(MAPSP), and methyl 6-O-methacryloyl-α-D-glucoside (6-O-MAMGlc). ApplyingDMAEMA, a polymer with molecular weight up to 17,500 Da and a PDI as low as1.20 was synthesised by gamma radiation in water.154 The radically initiated RAFTpolymerisation of MAPSP in water yielded molecular weights up to approximately100,000 Da, with PDIs below 1.10.147 Finally, 6-O-MAMGlc was polymerised withCTP in water.150 Addition of sodium carbonate or sodium hydrogen carbonate didnot offer control over the reaction, while addition of approximately 10% ethanolled to conformation of the molecular weight with its theoretical value. A molecularweight of 26,300 Da was reported, with a PDI of 1.14.

CTP was furthermore employed as RAFT agent for the polymerisation ofMEABSE in aqueous buffer, as well as MTBSPE and MTBSMPM in water.150

However, no polymer was obtained, while the distinct colour of the mixture wasretained. The latter was attributed to a low rate of polymerisation at the em-ployed temperature, which was confirmed by a very low rate of reaction when freeradical polymerisation was employed with this monomer. Finally, MAETA waspolymerised with MTBSPE in water up to a molecular weight of 60,000 Da, withPDI values of approximately 1.60 (determined by end-group analysis).150 Employ-ing ASEC, high molecular weights and PDIs were obtained, which was attributedto aggregation of the polymer because of electrostatic interaction between anionicend-groups and the cationic polymer.


O

OO

O

n





Methacrylates










O

OO

O

n





Methacrylates









Thesis1.indd 34 29-10-2017 11:02:35

1


O

OO

O

n





Methacrylates










O

OO

O

n





Methacrylates










O

OO

O

n





Methacrylates









Thesis1.indd 35 29-10-2017 11:02:36


Crosslinked polymers of PEGMA were synthesised in acetonitrile, in presenceof trithiocarbonate BCPA.167 In a first step, PEGMA was polymerised up to amolecular weight of 9,000 Da or 21,000 Da with PDI values below 1.20. Subse-quently, the macro RAFT agents were crosslinked with BisAM or a biodegradablecrosslinker, in presence of benzaldehyde, up to a molecular weight of 132,000 Dawith polydispersities between 1.08 and 1.19.

Other water soluble monomers

Besides (meth)acrylamides and (meth)acrylates, other water soluble monomers arereported in literature. Some of these monomers exhibit unique properties, suchas the introduction of ion exchange properties,179 which renders them promisingcandidates for several applications. Starch was modified with a xanthate group,similar to that of MCEX, and subsequently applied in the polymerisation of vinylacetate (VA).180 The molecular weight of one sample was listed, namely 263,000Da, with a PDI of 2.72. After hydrolysis, the arms were characterised and molecularweights of 18,000 to 105,000 Da were reported, with PDI values between 1.21 and1.53. VBTA was polymerised with ditbiobenzoate TBSPNDS and CTP. Withthe latter RAFT agent in aqueous NaBr, molecular weights up to 40,000 Da wereobtained, with a PDI below 1.14.147 A macro RAFT agent with a molecular weightof 27,300 Da and a PDI of 1.13 was employed in the polymerisation of DMA up toa molecular weight of 124,000, with a final PDI of 1.39. CTP was applied in water,yielding a polymer with a molecular weight of 5,800 Da and a PDI of 1.08.149 Thismacro RAFT agent was used in the polymerisation of DMAPMAM and VBTA.The former polymerisation turned out to be uncontrolled, while the latter yielded ablock copolymer with a molecular weight of 31,100 Da with a PDI of 1.14. Anotherlow molecular weight macro RAFT agent was synthesised with CTP and VBTA.134

A chain extension experiment was conducted with N,N -dimethylvinylbenzylamine(DMVBA) up to a molecular weight of 51,000 Da and a corresponding PDI of 1.37.

Sodium 4-vinylbenzenesulfonate (SSS) was polymerised with a variety ofdithiobenzoates. TBSPNDS was employed in aqueous NaBr, however, no molec-ular weights were reported.147 CTP was employed in water, yielding molecularweights up to 31,600 Da and PDI values below 1.26.134 A successful chainextension experiment was performed with sodium 4-vinylbenzoate (VB) and amacro RAFT agent of unknown molecular weight. The final molecular weight ofthe copolymer was 18,800 Da, with a PDI of 1.18. The latter research reportsthe polymerisation of SSS with CMDB in water as well. While a high molecularweight of 507,000 Da was obtained, conformation with its theoretical valuewas poor and the loss of control was confirmed by a high polydispersity.134

CTP, moreover, was modified with PEG, to yield a PEG chain capped betweentwo CTP dithiobenzoate structures with a molecular weight of 10,000 Da and

1.5. AIM AND SCOPE OF RESEARCH 33

a polydispersity of 1.18.153 The macro RAFT agent was subsequently chainextended with SSS in water up to a molecular weight of 18,800 Da and a PDI of1.24. Moreover, some unsuccessful RAFT polymerisations have been reported.Dithiobenzoates TBSPNDS, MTBSPE, and MTBSMPM have been employed inthe polymerisation of VPPS in aqueous NaBr, however, even at low a pH nopolymer was formed.147 Judging from the discolouration of the reaction mixture,failure of the reaction was attributed to degradation of the RAFT agents.

As shown in the overview above, multiple monomers have been employed inthe synthesis of water soluble polymers. However, little research is devoted tothe RAFT polymerisation of water soluble polymers up to high molecular weights.With respect to their application in EOR, molecular weight is one of the governingfactors. On top of that, little research is directed at the synthesis of branched,water soluble polymers, especially at a desirable higher molecular weight.

1.5 Aim and scope of research

The objective of this work is to investigate the use of reversible addition-fragmentation chain-transfer (RAFT) polymerisation in the preparation ofwater-soluble polymers for application in enhanced oil recovery (EOR). Becauseof the limited results available from literature, the focus is more specifically onthe introduction of branches in such polymers and on the comparison of thesepolymers with linear equivalents for application in EOR.

Chapter 1 gives an introduction to polymer flooding and the currently appliedcommercial polymers. Current polymers for EOR contain acrylamide (AM), asit is affordable and offers desirable viscosifying properties. AM can be readilypolymerised by free radical polymerisation up to high molecular weights, and watercan be applied as solvent. From literature, however, introducing branches in thepolymers has become apparent to yield advantages related to the rheology, aswell as to shear resistance and presence of salts. In order to introduce branchingin an industrially-relevant polymerisation procedure, control over the reaction isrequired. The latter can be offered by applying a controlled radical polymerisation(CRP) approach. Therefore, the state of the art on the controlled synthesis ofwater soluble polymers by RAFT polymerisation has been presented.

In Chapter 2, the synthesis of three different industrially relevant RAFT agentsis described. These RAFT agents are designed to offer control over the polymeri-sation of AM and influence the molecular weight of the final polymers.

In Chapter 3, RAFT agent 3-(((benzylthio)carbonothioyl)thio) propanoic acid(BCPA) is applied in the aqueous polymerisation of AM. Control over the reac-tion is investigated by linear first order kinetic plots, a linear development of themolecular weight as function of reaction time and a chain extension experiment































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of an AM macro RAFT agent with N,N -dimethylacrylamide (DMA). The workdescribed in this chapter opens the door to the polymerisation of AM up to highmolecular weight.

After the synthesis of linear PAM, the focus is on the introduction of branchesin the polymers. To that end, hyperbranched PAM is synthesised in Chapter 4by a facile copolymerisation of AM and N,N ’-methylenebis (acrylamide) (BisAM)in presence of a RAFT agent. The role of the RAFT agent is investigated, aswell as the degree of branching. The effectiveness of the introduction of branches isinvestigated by the comparison of a branched polymer to a linear equivalent (whichoffers a larger hydrodynamic volume than a branched counterpart).

The focus is shifted towards reaching higher molecular weights in Chapter 5,by application of a two-step synthetic approach. In the first step, a low molecularweight branched core is synthesised. This macro RAFT agent is extended withfresh AM in a second step. The effect of the degree of branching in the core, aswell as the length of the arms after extension (step 2) are investigated. Rheologicalmeasurements of these polymers are performed in Chapter 6. Elastic behaviour ofthe SB-PAMs is evaluated based on the amount of crosslinker in the core of thepolymer. The polymers are ultimately evaluated in a two-dimensional flow-cell, inorder to simulate oil recovery from an oil field and more specifically from dead-endsin such fields.

In Chapter 7, the properties of SB-PAMs with higher molecular weights are setin direct comparison with linear PAMs and commercial linear hydrolysed polyacry-lamides (HPAMs). These comparisons are performed in flow-cell experiments andin core flood experiments, which evaluates the oil recovery of the polymer solutionsfrom porous rock. Moreover, the effect of the addition of NaCl to the aqueouspolymer solutions is investigated.

In Chapter 8, the synthesis of novel thermothickening polymers is explored, asalternative to ultra high molecular weight conventional polymers for EOR. Combcopolymers containing 17 arms (on average) of N,N -dimethylacrylamide (DMA)and N -isopropylacrylamide (NIPAM) are prepared at 0 ◦C in water with the CRPmethod atom transfer radical polymerisation (ATRP). These copolymers are evalu-ated on their lower critical solution temperature (LCST), which is the temperatureat which the solubility of the polymer deteriorates. Altering the solubility of suchpolymers could render these polymers interesting from an application point of view,as the polymers can be injected into oil fields with low energy consumption (highshear rate and low temperature), whereas the solution viscosity increases where itis desirable (in the oil field, at a low shear rate and high temperature).

1.6. ACKNOWLEDGEMENT 35

1.6 Acknowledgement

This research forms part of the research program of the Dutch Polymer Institute,Project 778.

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Thesis1.indd 45 29-10-2017 11:02:48


Supplementary Information Chapter 1

Table S1: (Meth)acrylamides

Structure Monomer Abbreviation

O NH2 Acrylamide AM

O NH2 Methacrylamide MAM

O N

N,N -dimethylacrylamide DMA

O NH

N -isopropylacrylamide NIPAM

O N

O N -acryloylmorpholine NAM

O NH

NH2 N -(2-aminoethyl)acrylamide AEMA

O NH

NH2 N -(3-aminopropyl)acrylamide APMA

O NH

OH

N -(2-hydroxypropyl) methacry-lamide HPMA

O NH Cl-

NH+ N -(3-(dimethylamino)propyl)acrylamide DMAPAM

O NH

SOH

O

O 2-acrylamido-2-methylpropanesulfonic acid AMPS

O NH Cl-

NH+ N -(3-(dimethylamino)propyl)methacrylamide DMAPMAM

1.6. SUPPLEMENTARY INFORMATION CHAPTER 1 43

Table S2: Acrylates


O OH Acrylic acid AA

O OOH

n Polyethylene glycolacrylate PEGA

O OOH

2-Hydroxyethyl acrylate HEA

O ON+

Cl- 2-Acryloyloxyethyl)trimethylammonium chloride AETA

O O SO

OO- K+

3-(Acryloyloxy)propanesulfonatepotassium salt APSP

Table S3: Methacrylates


O OH Methacrylic acid MAA

O OOH

n

Poly(ethyleneglycol) methacry-late PEGMA

O ON

N,N -Dimethylaminoethylmethacrylate DMAEMA

O ON+

Cl-(2-Methacryloyloxyethyl)trimethylammonium chloride MAETA

O O SO

OO- K+ 3-(Methacryloyloxy) propanesul-

fonate potassium salt MAPSP

OOS

O

OO- K+

OOS

O-

O

OK+

2-Methylenesuccinic acid bis(3-sulfopropyl) ester dipotassiumsalt MEABSE

O O

OHO

HO

OOH Methyl 6-O-methacryloyl-

α-D-glucoside 6-O-MAMGlc





O NH2 Acrylamide AM


O N


O NH


O N


O NH


O NH


O NH

OH


O NH Cl-


O NH

SOH

O


O NH Cl-



Table S2: Acrylates



O OOH


O OOH


O ON+


O O SO

OO- K+





O OOH

n


O ON


O ON+


O O SO



OOS

O

OO- K+

OOS

O-

O

OK+


O O

OHO

HO







O NH2 Acrylamide AM


O N


O NH


O N


O NH


O NH


O NH

OH


O NH Cl-


O NH

SOH

O


O NH Cl-



Table S2: Acrylates



O OOH


O OOH


O ON+


O O SO

OO- K+





O OOH

n


O ON


O ON+


O O SO



OOS

O

OO- K+

OOS

O-

O

OK+


O O

OHO

HO



Thesis1.indd 46 29-10-2017 11:02:50

1





O NH2 Acrylamide AM


O N


O NH


O N


O NH


O NH


O NH

OH


O NH Cl-


O NH

SOH

O


O NH Cl-



Table S2: Acrylates



O OOH


O OOH


O ON+


O O SO

OO- K+





O OOH

n


O ON


O ON+


O O SO



OOS

O

OO- K+

OOS

O-

O

OK+


O O

OHO

HO







O NH2 Acrylamide AM


O N


O NH


O N


O NH


O NH


O NH

OH


O NH Cl-


O NH

SOH

O


O NH Cl-



Table S2: Acrylates



O OOH


O OOH


O ON+


O O SO

OO- K+





O OOH

n


O ON


O ON+


O O SO



OOS

O

OO- K+

OOS

O-

O

OK+


O O

OHO

HO







O NH2 Acrylamide AM


O N


O NH


O N


O NH


O NH


O NH

OH


O NH Cl-


O NH

SOH

O


O NH Cl-



Table S2: Acrylates



O OOH


O OOH


O ON+


O O SO

OO- K+





O OOH

n


O ON


O ON+


O O SO



OOS

O

OO- K+

OOS

O-

O

OK+


O O

OHO

HO



Thesis1.indd 47 29-10-2017 11:02:52


Table S4: Other water soluble monomers


O

O Vinyl acetate VA

N+

Cl-

(Ar-vinylbenzyl) trimethylam-monium chloride VBTA

SO-O

O

Na+ Sodium 4-vinylbenzenesulfonate SSS

N+ SO-

O

O

3-(2-Vinylpyridinio) propanesul-fonate VPPS

2Synthesis of RAFT Agents for Aqueous

Polymerisation of Acrylamide

Adapted from: van Mastrigt, F., Ferrero Lopez, N., van Oosterhout, H.N., Roelfes,J.G. & Picchioni, F. (2017). Synthesis of RAFT Agents for Aqueous Polymerisa-tion of Acrylamide. To be submitted.

45




O

O Vinyl acetate VA

N+

Cl-


SO-O

O


N+ SO-

O

O





45




O

O Vinyl acetate VA

N+

Cl-


SO-O

O


N+ SO-

O

O





45

Thesis1.indd 48 29-10-2017 11:02:52

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