research article effect of temperature and catalyst concentration...

Research ArticleEffect of Temperature and Catalyst Concentration onPolyglycerol during Synthesis

Carolina Ardila-Suaacuterez1 Diana Rojas-Avellaneda12 and Gustavo E Ramirez-Caballero13

1Grupo de Investigacion en Polımeros Escuela de Ingenierıa Quımica Universidad Industrial de Santander (UIS)Bucaramanga Colombia2Grupo de Investigacion en Materiales Afaltos y Mezclas Asfalticas para Pavimentos Flexibles CorasfaltosPiedecuesta Colombia3Centro de Investigaciones en Catalisis Escuela de Ingenierıa Quımica Universidad Industrial de Santander (UIS)Bucaramanga Colombia

Correspondence should be addressed to Gustavo E Ramirez-Caballero gusramcauiseduco

Received 16 June 2015 Revised 13 September 2015 Accepted 15 September 2015

Academic Editor Yu Wang

Copyright copy 2015 Carolina Ardila-Suarez et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Morphology molecular weight polydispersity functionality and thermal properties are important characteristics when usingpolyglycerol as a building block in the development of materials for industrial applications such as hydrogels surfactants asphaltsadditives cosmetics pharmaceutical biomedical and drug delivery systems In this study several experimental techniques areused to understand the effect of process variables during synthesis in the catalyzed etherification of glycerol a coproduct ofbiodiesel industry Biobased polyglycerol is a high-valued product which is useful as building block material because of itsremarkable features for instance multiple hydrophilic groups excellent biocompatibility and highly flexible aliphatic polyetherbackbone A connection between polyglycerol characteristics and process variables during synthesis allows the control of glycerolpolymerization through reaction conditions We show that temperature and catalyst concentration can be tuned with the aim oftailoring fundamental polyglycerol parameters including molecular weight polydispersity morphology and functionality

1 Introduction

Polyglycerol obtained from direct catalytic etherification ofglycerol is a biobased polymer used as a building blockfor several applications such as hydrogels [1ndash3] emulsifiers[4 5] catalyst supports [6] and biomedical applications [7ndash9] Industrial and academic interest on glycerol as a rawmaterial for polyglycerol synthesis are based on environ-mental and economic aspects This is because a biobasedmonomer is used for sustainable polymer production andproducing a value-added product from a coproduct fromthe biodiesel industry contributes to the transformation ofthis industry into a biorefinery [10] Synthesis of polyglycerolis currently gaining importance due to its remarkable fea-tures including flexible polyether backbone biocompatibilityand high number of hydrophilic functional groups which

increases polyglycerol versatility and enables the productionof complex polymeric structures Properties of polyglycerol-based materials are highly influenced by polyglycerol mor-phology functionality molecular weight polydispersity andthermal properties [11] Control of glycerol polymerizationto selectively produce desired polyglycerol materials withspecific characteristics is a scientific challenge that might beaddressed by tuning synthesis conditions

Polyglycerols can be produced fromvarious rawmaterialsand polymerization methods for instance glycidol andglycerol carbonate react via one-step anionic ring-openingpolymerization [12 13] and glycerol reacts via step-growthpolymerization [14] Several studies have reported the cat-alytic oligomerisation of glycerol using homogeneous andheterogeneous acid and base-catalyzed etherification [15 16]Most of the reaction products from these catalytic studies are

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2015 Article ID 910249 8 pageshttpdxdoiorg1011552015910249

2 International Journal of Polymer Science

lowmolecular weight oligomers An exception is the reactionwith sulfuric acid homogeneous catalyst which yields rela-tively high molecular weight polyglycerols [14] A previousstudy on themorphology of glycerol etherification derivativesconducted with 13C NMR reported carbon assignments forlinear branched and cyclic structures [17] Results of polyg-lycerol 13C NMR spectroscopy showed that homogeneousacid-catalyzed polymerization of glycerol at high tempera-tures favors the occurrence of branched structures [14] Toour knowledge there are no previous reports on the effect ofcatalyst concentration on polyglycerolmorphology producedfrom glycerol or on the combined effect of temperature andcatalyst concentration on polyglycerol properties

In this work polyglycerol is obtained from glycerol bya step-growth polymerization reaction using sulfuric acidas catalyst The effect of tuning temperature and catalystconcentration during synthesis conditions on the parame-ters that affect polyglycerol morphology hydroxyl numbermolecular weight polydispersity functionality and thermalproperties were studied Our goal is to provide guidelinesfor the polyglycerol synthesis from glycerol yielding specificproduct characteristics by varying temperature and catalystconcentration during synthesis The experimental strategyperformed in this study was based on a combinatorialexperiment with temperature and catalyst concentration ofsynthesis as factors This approach allows considering possi-ble interactions between factorsThe techniques used includematrix-assisted laser desorption and ionization time-of-flightspectrometry (MALDI-TOF) nuclear magnetic resonancespectroscopy (NMR) and differential scanning calorimetryanalysis (DSC) This paper is organized as follows firstmaterials reaction procedure and polymer characterizationtechniques are described second results of infrared spec-troscopic analysis (FT-IR) of synthesized polyglycerol fromglycerol are discussed and third the analysis of resultsis presented Finally conclusions of the main findings arereported

2 Experimental

21 Materials Materials used for the synthesis were obtainedfrom different vendors glycerol (85) sulfuric acid (95)phenolphthalein indicator and sodium hydroxide (99)were purchased from Merck acetic anhydride was obtainedfrom Carlo Erba and pyridine (95) fromMallinckrodt

22 Reaction Procedure Polymerization reactions were car-ried out in 50mL closed glass reactor in an inert envi-ronment (nitrogen atmosphere) Water was continuouslyremoved from the reaction mixture with a vacuum pumpGlycerol (20mL) polymerization reaction temperature wasvaried from 130∘C to 170∘C with a heating bath controlCatalyst concentrationwasmodified from 15 (ww) to 52(ww) All the reactions were carried out at 24 inches ofHg Polymerization products were neutralized with a NaOH01N solution and dried at 80∘C for 24 h without furtherpurification process

23 Polymer Characterization Polymerization reaction pro-ducts were analyzed using Fourier transform infrared spec-troscopy (FTIR) to identify functional groups Infraredspectra were obtained in transmittance mode in a ThermoScientific Spectrometer (Nicolet 1550 FT-IR)

Hydroxyl numbers were calculated following the ASTMD 4274-11 method Polymer samples were acetylated withan acetic anhydride-pyridine solution The unreacted acety-lation reagent was hydrolyzed with water and the aceticacid titrated with 05N sodium hydroxide solution Thehydroxyl content was calculated from the difference intitration between the acetic anhydride-pyridine solution usedas a blank and sample solutions

Molecular weight distributions of different reaction prod-ucts were obtained using MALDI-TOF-MS measurementsperformedwith a Bruker Reflexmass spectrometer equippedwith a nitrogen laser delivering 3 ns laser pulses at 337 nmRecrystallized 120572-cyano-4-hydroxycinnamic acid (10mgmL)in 30 70 (vv) acetonitrilewater containing 01 (vv)trifluoroacetic acid (TFA) was used as the matrix Sodiumchloride solution was used as cationization agent Polymersamples were dissolved in water to a final concentration of10 120583gmL An aliquot of the matrix (08 120583L) was applied toa multistage target until solvent evaporation subsequently01 120583L of cationization agent and 02120583L of sample were added

Polymer morphology analyses were performed using 13CNMR quantitative spectra taken on a Bruker Ultrashield400MHz (Avance III 400)TheDistortionless Enhancementby Polarization Transfer (DEPT) techniquewas used to deter-mine peaksmultiplicity Samples were prepared by dissolvingthe polymer in deuterated water to a final concentration of250 gL

Glass transition temperatures were obtained using Dif-ferential Scanning Calorimetry (DSC)measurements carriedout on a DSC Discovery TA Instruments Inc (USA) Sam-ples were subjected to two heating scans with the followingtemperature program first heating scan from minus80 to 200∘C ata heating rate of 5∘Cmin subsequently cooling to minus90∘C ata heating rate of 10∘Cmin and finally a second heating scanfrom minus90∘C to 400∘C at a heating rate of 5∘Cmin All scanswere performed under nitrogen purge gas of 50mLmin

3 Results and Discussion

The analysis of results was statistically supported using acombinatorial experimental design with temperature andcatalyst concentration as factors Each factor was evaluatedat three different levels that is temperatures of 130∘C 150∘Cand 170∘C and catalyst concentrations of 15 (ww) 335(ww) and 52 (ww) The response variables to ana-lyze were polyglycerol hydroxyl number molecular weightand polydispersity To determine polyglycerol morphologyand thermal properties a second experimental design wasperformed This time the factors were evaluated at twodifferent levels of temperature 130∘C and 150∘C and catalystconcentrations 15 (ww) and 52 (ww) Experimentaltest sequences were randomized and three replicates per levelwere taken

International Journal of Polymer Science 3

Table 1 Summary table of polyglycerol hydroxyl numbers obtainedunder different synthesis conditions at three temperatures andcatalyst concentrations Standard deviations were calculated basedon triplicates Three replicates per assay were taken

Temperature (∘C) Catalyst (ww) Hydroxyl number(mgKOHg)

130 15 6104 plusmn 205130 335 4412 plusmn 42130 52 5661 plusmn 124150 15 5258 plusmn 284150 335 506 plusmn 23150 52 3901 plusmn 133170 15 4131 plusmn 238170 335 3181 plusmn 295170 52 3706 plusmn 207

O-H C-H C-O

Tran

smitt

ance

() Catalyst 52 (ww)

Catalyst 15 (ww)

4000 3500 3000 2500 2000 10001500

Temperature 130∘C

Temperature 170∘C

Wavenumber (cmminus1)

Figure 1 FT-IR spectra of the reaction products of glycerolpolymerization performed at 130∘C with a catalyst concentration of15 (ww) and at 170∘C with catalyst concentration of 52 (ww)The obtained spectra are similar to previously reported polyglycerolspectra [1]

Fourier transform infrared spectroscopy (FT-IR) analyseswere conducted for all reaction products obtained from theexperimental design Results show that functional groupspresent in the reaction polymerization products are thesame as polyglycerol functional groups identified in previousresearch studies [14] For instance OH stretching bands at3000 cmminus1 to 3600 cmminus1 are related to polyglycerol terminalhydroxyl groups broad alkyl stretching bands (C-H) areobserved at 2883 and 2947 cmminus1 and bands ranged from950 to 1150 cmminus1 (C-O stretching) are related to polyglycerolpolyether chains FT-IR spectra of two samples at differentreaction conditions are shown in Figure 1 Those samplescorrespond to the products of glycerol polymerization per-formed at 130∘C and 170∘C at a catalyst concentration of 15(ww) and 52 (ww) respectively

31 Polyglycerol Hydroxyl Number Results from combinato-rial experiments with hydroxyl number as response variableare shown in Table 1 It is shown that hydroxyl numbers

15

335

52130150

170200

300

400

500

600

700

Hyd

roxy

l num

ber (

mg

KOH

g)

Temperature ( ∘C)

Catalyst concentration (

) (ww)

Figure 2 Temperature and catalyst concentration effect on polyg-lycerol hydroxyl number obtained from glycerol polymerizationCatalyst concentrations are shown 15 (ww) in red 335 (ww)in green and 52 (ww) in blue

of reaction products are lower than the initial hydroxylnumber of glycerol which is 1800 [mgKOHg] [18] Thisresult is expected since homogeneous acid-catalyzed step-growth polymerization of glycerol proceeds by splitting awater molecule for each ether linkage formed decreasing thenumber of hydroxyls in the reaction product [14]

The experimental results show that polyglycerol func-tionality can be tuned with the reaction conditions becausetemperature (119875 value lt 00001) catalyst concentration (119875value 00007) and the interaction between these two factors(119875 value 00031) have a significant effect on polyglycerolhydroxyl number Temperature is the factor with the greatesteffect followed by catalyst concentration and the interactionbetween factors respectively see Figure 2

At fixed catalyst concentration of 15 (ww) and 52(ww) the polyglycerol hydroxyl number decreases as tem-perature increases For instance at catalyst concentrationof 52 (ww) polyglycerol hydroxyl numbers at 130∘C150∘C and 170∘C were 5661 plusmn 124 3901 plusmn 133 and3706 plusmn 207mgKOHg respectively A different trend wasfound at fixed catalyst concentration of 335 (ww) wherepolyglycerol has the higher hydroxyl number at 150∘C with5060 plusmn 23mgKOHg followed by 130∘C and 170∘C withhydroxyl numbers of 4412plusmn42 and 3181plusmn295mgKOHgrespectively

At fixed reaction temperatures of 130∘C and 170∘Cpolyglycerol has the lower hydroxyl number using a catalystconcentration of 335 (ww) with 4412 plusmn 42 and 3181 plusmn295mgKOHg respectively followed by catalyst concentra-tion of 15 (ww) and 52 (ww) with hydroxyl numbers at130∘Cof 6104plusmn205 and 5661plusmn124mgKOHg and hydroxylnumbers at 170∘C of 4131plusmn238 and 3706plusmn207mgKOHgrespectively On the other hand at fixed reaction temperatureof 150∘C as catalyst concentration increases polyglycerolhydroxyl number decreases with hydroxyl numbers of 5258plusmn284 506 plusmn 23 and 3901 plusmn 133mgKOHg using catalyst


Catalyst 15 (ww)

2400 2600 2800 3000 3200 3400 3600 3800mz

Temperature 130∘C

(a)

2400 2600 2800 3000 3200 3400 3600 3800

Catalyst 52 (ww)

mz

Temperature 170∘C

(b)

Figure 3 Polyglycerol molecular weight distributions determined with MALDI-TOF spectra of two samples (a) Polyglycerol synthesized at130∘C and 15 (ww) catalyst concentration and (b) polyglycerol synthesized at 170∘C and 52 (ww) catalyst concentration

concentrations of 15 (ww) 335 (ww) and 52 (ww)respectively Results show that catalyst concentration failsto produce the same trend effect on polyglycerol hydroxylnumber at different levels of temperature since these twofactors interact

Thedecrease of hydroxyl number in the reaction productswith respect to initial hydroxyl number of glycerol is dueto chemical reactions that involve hydroxyl group reactionssuch as etherification reactions and cyclization [14 17] Theresults showed that temperature and catalyst concentrationimpact conversion of these reactions Higher temperature orcatalyst concentration increases reaction conversion resultingin a decrease of hydroxyl groups in reaction products Resultsalso showed that temperature and catalyst concentration arefactors that interact as a result the impact of temperature onhydroxyl number varies depending on catalyst concentration

32 MolecularWeight Distribution of Synthesized PolyglycerolTemperature and catalyst concentrations do not have a sig-nificant effect on polyglycerol molecular weight and polydis-persity The number and weight average molecular weightsas well as the polydispersity of each treatment establishedby the combinatorial design are shown in Table 2 Averagevalues of molecular weights distributions (Mw and Mn) andpolydispersity for all treatments were 29178Da 29853Daand 1023 respectively Calculated molecular weights (Mw)are in agreement with previously reported number averageMw of polyglycerol synthetized at 140∘C and pressures below26 kPa [14] which is consistent with our findings regardingthe fact that the number average Mw is not significantlyaffected by temperature and catalyst concentration Figure 3shows the MALDI-TOF mass spectra analysis of treatmentswith temperatures of 130∘C and 170∘C and catalyst concen-trations of 15 (ww) and 52 (ww) respectively

The fact that higher temperature and catalyst concentra-tion decrease hydroxyl number of reaction product but donotdecrease polyglycerol molecular weight and polydispersitysuggests that temperature and catalyst concentration areaffecting polyglycerol morphology As will be shown in thenext section temperature and catalyst concentration affectreaction selectivity of glycerol hydroxyl groups Higher tem-perature and catalyst concentration favor reaction of glycerolsecondary hydroxyl group forming polyglycerol branchedstructures

Table 2 Summary table of polydispersity number and weight aver-age molecular weights of polyglycerol synthesized at three differenttemperatures (130 150 and 170∘C) and catalyst concentrations 15(ww) 335 (ww) and 52 (ww)

Temperature (∘C) Catalyst (ww) Mw (Da) Mn (Da) PD

130 15 29872 29191 1023130 335 29865 29176 1024130 52 29762 29089 1023150 15 29782 29103 1023150 335 29783 29113 1023150 52 30124 29432 1023170 15 29911 29245 1023170 335 29756 29082 1023170 52 29825 29172 1022

33 Polyglycerol Morphology Branched structures terminalunits and polyether chains within the polyglycerol structurewhich ultimately define polyglycerol morphology were iden-tified in the polyglycerol samples obtained under differentsynthesis conditions and analyzed using the 13C NMR spec-troscopy technique (Table 3) Peak analysis between quan-titative 13C NMR and DEPT spectra was made to establishpolyglycerol morphology The 13C NMR spectra region from60 to 64 ppm indicates the presence of -CH

2OH carbons

of polyglycerol terminal units which are primary hydroxylgroups the signal region from 68 to 73 ppm indicates thepresence of -CHOH- carbons which are pending hydroxylgroups the region from 72 to 73 ppm indicates -CH

2-O-

carbons which are polyether chains and that from 74 to82 ppm indicates the presence of -CH-O- carbons related tothe beginning of branched chains [12 17] Table 4 shows thefunctional groups found at specific peak intervals at each par-ticular temperature and catalyst concentration An exampleof a quantitative 13C NMR spectrum performed at 130∘C and15 (ww) catalyst concentration is shown in Figure 4 wherethe 13C NMR spectrum regions analyzed are highlighted

The results of polyglycerol morphology were calculatedtaking the relative area under spectra signals in the spectraregion that identify each kind of carbon described in Table 4

The results show that temperature catalyst concentrationand their interaction have a significant effect on polyglycerol


Table 3 Temperature (∘C) catalyst concentration (ww) and relative area under spectra region used to quantify and identify differentpolyglycerol carbons All experiments were carried out in duplicate

Temperature(∘C)

Catalyst (ww)

-CH2OH carbons

60ndash64 ppmterminal units

()

-CHOH- -CH2-O- carbons

68ndash73 ppmpolyether chains and pending

hydroxyl groups()

-CH-O- carbons74ndash82 ppm branching

()

130 15 461 plusmn 05 518 plusmn 14 20 plusmn 09130 52 501 plusmn 03 477 plusmn 08 22 plusmn 05150 15 306 plusmn 12 611 plusmn 06 83 plusmn 06150 52 142 plusmn 00 559 plusmn 03 299 plusmn 03

Table 4 Model of glycerol polymerization growing chain containing linear branched and cyclic segments and their carbons assignments by13C NMR (see also Scheme 1) [12 14 17]

Carbon type (120575 13C in ppm)-CH2OH -CHOH- -CH

2-O- -CH-O-

60ndash64 ppmPolyglycerol terminal units(primary hydroxyl groups)

68ndash73 ppmpendant hydroxyl groups

72-73 ppmpolyether chains

74ndash82 ppmbranching

C-1 C-9 C-171015840 C-27 and C-271015840 C-2 C-6 C-161015840 C-1610158401015840 and C-26

C-3 C-5 C-7 C-9 C-13 C-15C-131015840 C-151015840 C-17 C-19 C-191015840C-171015840 C-23 C-25 C-1510158401015840 C-261015840

C-251015840 and C-231015840

C-10 C-12 C-20 andC-22

HO O

OH

O

HO

OO

HO

O

OH

HO

OH

OO

O

O

O

OHOH

O OHHO

1

2

3

4

5

6

7

8

9

1011

12

1314

15

16

1718

1920

2122

23 24 2526

27

15

9998400

1699840016998400

19998400

1799840017998400

14998400

1399840018998400

1599840025998400

24998400

23998400

26998400

27998400

Scheme 1

Quantitative 13C NMR

Catalyst 15 (ww)

Polyglycerolterminal units

Branching

-CH-O- -CHOH-

Pendanthydroxyl groups

Polyetherchains

-CH2-O- -CH2OH

Temperature 130∘C 800070006000500040003000200010000

81 80 79787776757473727170696867666564636261605958

f1 (ppm)

Figure 4 Quantitative 13CNMR spectra of the polyglycerol synthe-sized at 130∘C and 15 (ww) catalyst concentrations

morphology (119875 valuelt 00001)This result suggests that thesefactors impact reaction selectivity of hydroxyl groups Theincrement of these factors favors secondary hydroxyl groupreaction varying polyglycerol morphology Temperature is

the factor with the greatest effect on polyglycerol morphol-ogy At fixed catalyst concentration of 52 (ww) as temper-ature increases from 130 to 150∘C polyglycerol terminal unitsdecrease from 501 to 142 polyglycerol polyether chainsincrease from 477 to 559 and branching increases from22 to 2986 respectively Same trend is observed at fixedcatalyst concentration of 15 (ww) however the impactof temperature on polyglycerol morphology diminishes atlower catalyst concentration revealing the existence of aninteraction between these two factors At fixed temperatureof 130∘C the increment of catalyst concentration from 15to 52 (ww) has a slight effect on polyglycerol terminalunits (from 461 to 501) polyether chains (from 518to 477) and branching (from 2 to 22) On the otherhand at fixed temperature of 150∘C the increment of cata-lyst concentration has a considerable effect on polyglycerolterminal units (from 306 to 142) polyether chains (from611 to 559) and branching (from 83 to 299) Thesechanges in the impact of catalyst concentration as a functionof temperature are due to interaction between factors


03

02

01

00

minus01

minus02

minus03

minus04

minus05

minus06

minus90

minus70

minus50

minus30

minus10 10 30

50

70

90

110

130

150

170

190

210

230

250

2

2

3

3

3

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)

PG 15 (ww)-150∘C

Second heating scan

First heating scan

1

1

(a)

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)

minus40 minus35 minus30 minus25 minus20 minus15 minus10 minus5 0 5

PG 15 (ww)-130∘C

PG 15 (ww)-150∘C

PG 52 (ww)-130∘C

PG 52 (ww)-150∘C

(b)

Figure 5 (a) First and secondheating scanDSC results for polyglycerol synthetizedwith catalyst concentration of 15 (ww) and temperatureof 150∘C (b) Polyglycerol glass transition temperatures found in the second heating scan

34 Polyglycerol Glass Transition Temperature Polyglycerolglass transition temperature marks the change from glassyor energy-elastic state to a rubbery or entropy driven-elastic stateThus the knowledge of this polyglycerol thermalproperty is essential in the selection of this material forvarious applications

Glass transition temperatures were determined usingDSC experimental procedure that was performed in twoheating scans The first scan was performed to reveal infor-mation about the current conditions of polyglycerol Forinstance processing influences an effect of attached water tothe polar hydroxyl groups on thermal properties [19] Aftercooling a second heating scan was performed to determineparticular properties of polyglycerol without the influence ofvolatile substances and processing

In the first heating scan glass transition temperatureswere observed at temperatures below minus50∘C As heatingprogresses water begins to evaporate at around 30∘C causingan endothermic change in the heating curve The particularstrong bond between water and polyglycerol hydroxyl groupsmakes the diffusion of water through polyglycerol difficultresulting in an endothermic change in the heating curvethat went up to 200∘C After cooling during the secondheating scan glass transition temperatures increased and theendothermic change in the heating curve disappeared

Statistical analysis suggests that polyglycerol glass tran-sition temperature is significantly affected by catalyst con-centration (119875 value 00002) temperature (119875 value 00002)and the interaction between these two factors (119875 value lt00001) The interaction between temperature and catalystconcentration is the factor with the greatest effect Forinstance at fixed catalyst concentration of 15 (ww) anincrement in temperature from 130∘C to 150∘C caused theglass transition temperature to decrease from minus86∘C tominus253∘C On the other hand at catalyst concentration of 52

(ww) and the same temperature change from 130∘C to 150∘Cthe glass transition temperature increased from minus186∘C tominus8∘C Similar trend was found at fixed temperatures of 130∘Cand 150∘C varying catalyst concentration from 15 (ww) to52 (ww) at 130∘C caused the glass transition temperatureto decrease whereas varying catalyst concentration from 15(ww) to 52 (ww) at 150∘C caused the glass transitiontemperature to increase showing interaction between factors

Polyglycerol glass transition temperature depends onboth polymer branching structure and the amount of -OHhydrophilic groups It has been reported that an increase ofpolymer branching leads a restriction of segmental mobilitywhich increases glass transition temperature [20] Similarlyhydrophilic groups in the polymer chemical structure like -OH capable of hydrogen bonding affect glass transition tem-perature [21 22] Since catalyst concentration and tempera-ture influence polyglycerol hydroxyl number and branchingin an opposite way when polyglycerol hydroxyl numberdecreases branching increases there is a competition inthe impact of hydroxyl number and branching on polyg-lycerol glass transition temperature For instance at fixedcatalyst concentration of 52 a change of temperature from130∘C to 150∘C decreases polyglycerol hydroxyl number from566mgKOHg to 390mgKOHg but increases polyglycerolbranching from 22 to 299 In this case polyglycerolbranching has more impact on glass transition temperaturesince it increases from minus18∘C to minus8∘C On the other hand atfixed temperature of minus130∘C a change of catalyst concentra-tion from 15 to 52 decreases polyglycerol hydroxyl num-ber from 610mgKOHg to 566mgKOHg and the change ofpolyglycerol branching is negligible from 2 to 22Thus inthis case the polyglycerol hydroxyl number has more impacton decreasing polyglycerol glass transition temperature fromminus86∘C to minus186∘C as shown in Figure 5


4 Conclusions

New insights have been obtained regarding the effect ofsynthesis conditions of production of polyglycerol from glyc-erol on the final polyglycerol morphology molecular weightpolydispersity thermal properties and functionality Tem-perature and catalyst concentration of synthesis enable thesynthesis of polyglycerol with specific fundamental param-eters that determine polyglycerol final applications Theincrease of temperature of synthesis decreases polyglycerol-OH terminal units increases polyglycerol polyether chainsand pending hydroxyl groups increases polyglycerol branch-ing and decreases polyglycerol hydroxyl number In generalthe impact of temperature of synthesis on morphology andfunctionality escalates significantly at higher catalyst concen-tration Changes in polyglycerol morphology and functional-ity affect glass transition temperature due to changes in polyg-lycerol branching degree and hydroxyl number Furthermorepolyglycerol molecular weight and polydispersity were notsignificantly affected by variations in temperature and catalystconcentration during the process of synthesis

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This study is supported by the Office of the Research andCommunity Outreach Provost at Universidad Industrial deSantander (UIS) through a research grant (code 5459) theagreement of cooperation (code 0727) between UIS Univer-sity and Colciencias and the agreement of cooperation (code65061538329) between Corasfaltos and Colciencias The MassSpectroscopy and Nuclear Magnetic Resonance laboratoriesof UIS University are also gratefully acknowledged Theauthors thank Drs Andrea Garzon and Perla Balbuena forcarefully reviewing this paper

References

[1] S Salehpour C J Zuliani and M A Dube ldquoSynthesis ofnovel stimuli-responsive polyglycerol-based hydrogelsrdquo Euro-pean Journal of Lipid Science and Technology vol 114 no 1 pp92ndash99 2012

[2] X Yang and L Liu ldquoSynthesis and characterization of novelpolyglycerol hydrogels containing L-lactic acid groups aspendant acidic substituents pH-responsive polyglycerol-basedhydrogelsrdquo Journal of Applied Polymer Science vol 112 no 6 pp3209ndash3216 2009

[3] M H M Oudshoorn R Rissmann J A Bouwstra and WE Hennink ldquoSynthesis and characterization of hyperbranchedpolyglycerol hydrogelsrdquo Biomaterials vol 27 no 32 pp 5471ndash5479 2006

[4] I Gulseren and M Corredig ldquoInteractions between polyg-lycerol polyricinoleate (PGPR) and pectins at the oil-waterinterface and their influence on the stability of water-in-oilemulsionsrdquo Food Hydrocolloids vol 34 pp 154ndash160 2014

[5] K Matsumiya Y Takahashi K Nakanishi N Dotsu andY Matsumura ldquoDiglycerol esters of fatty acids promotesevere coalescence between protein-stabilized oil droplets byemulsifier-protein competitive interactionsrdquo Food Hydrocol-loids vol 42 no 3 pp 397ndash402 2014

[6] V S Thengarai J Keilitz and R Haag ldquoHyperbranchedpolyglycerol supported ruthenium catalysts for ring-closingmetathesisrdquo Inorganica Chimica Acta vol 409 pp 179ndash1842014

[7] J-P Boudou M-O David V Joshi H Eidi and P A CurmildquoHyperbranched polyglycerol modified fluorescent nanodia-mond for biomedical researchrdquoDiamond andRelatedMaterialsvol 38 pp 131ndash138 2013

[8] K Hoger T Becherer W Qiang R Haag W Frieszlig andS Kuchler ldquoPolyglycerol coatings of glass vials for proteinresistancerdquo European Journal of Pharmaceutics and Biopharma-ceutics vol 85 no 3 pp 756ndash764 2013

[9] D Steinhilber M Witting X Zhang et al ldquoSurfactant freepreparation of biodegradable dendritic polyglycerol nanogelsby inverse nanoprecipitation for encapsulation and releaseof pharmaceutical biomacromoleculesrdquo Journal of ControlledRelease vol 169 no 3 pp 289ndash295 2013

[10] M Ayoub and A Z Abdullah ldquoCritical review on the currentscenario and significance of crude glycerol resulting frombiodiesel industry towards more sustainable renewable energyindustryrdquoRenewable and Sustainable EnergyReviews vol 16 no5 pp 2671ndash2686 2012

[11] W Daniel S-E Stiriba and F Holger ldquoHyperbranchedpolyglycerols from the controlled synthesis of biocompatiblepolyether polyols to multipurpose applicationsrdquo Accounts ofChemical Research vol 43 no 1 pp 129ndash141 2010

[12] A Sunder R Hanselmann H Frey and R Mulhaupt ldquoCon-trolled synthesis of hyperbranched polyglycerols by ring-opening multibranching polymerizationrdquoMacromolecules vol32 no 13 pp 4240ndash4246 1999

[13] G Rokicki P Rakoczy P Parzuchowski and M SobieckildquoHyperbranched aliphatic polyethers obtained from environ-mentally benign monomer glycerol carbonaterdquo Green Chem-istry vol 7 no 7 pp 529ndash539 2005

[14] S Salehpour andM A Dube ldquoTowards the sustainable produc-tion of higher-molecular-weight polyglycerolrdquoMacromolecularChemistry and Physics vol 212 no 12 pp 1284ndash1293 2011

[15] A Martin andM Richter ldquoOligomerization of glycerolmdasha crit-ical reviewrdquo European Journal of Lipid Science and Technologyvol 113 no 1 pp 100ndash117 2011

[16] M V Sivaiah S Robles-Manuel S Valange and J BarraultldquoRecent developments in acid and base-catalyzed etherificationof glycerol to polyglycerolsrdquo Catalysis Today vol 198 no 1 pp305ndash313 2012

[17] S Cassel C Debaig T Benvegnu et al ldquoOriginal synthesis oflinear branched and cyclic oligoglycerol standardsrdquo EuropeanJournal of Organic Chemistry vol 2001 no 5 pp 875ndash896 2001

[18] M L Maminski R Szymanski P Parzuchowski A Antczakand K Szymona ldquoHyperbranched polyglycerols with bisphenolA core as glycerol-derived components of polyurethane woodadhesivesrdquo BioResources vol 7 no 2 pp 1440ndash1451 2012

[19] J Gupta CNunes and S Jonnalagadda ldquoAmolecular dynamicsapproach for predicting the glass transition temperature andplasticization effect in amorphous pharmaceuticalsrdquoMolecularPharmaceutics vol 10 no 11 pp 4136ndash4145 2013


[20] Q Zhu J Wu C Tu et al ldquoRole of branching architecture onthe glass transition of hyperbranched polyethersrdquo The Journalof Physical Chemistry B vol 113 no 17 pp 5777ndash5780 2009

[21] A Khalyavina L Hauszligler and A Lederer ldquoEffect of the degreeof branching on the glass transition temperature of polyestersrdquoPolymer vol 53 no 5 pp 1049ndash1053 2012

[22] C Xi L Sztandera and H M Cartwright ldquoA neural networkapproach to prediction of glass transition temperature of poly-mersrdquo International Journal of Intelligent Systems vol 23 no 1pp 22ndash32 2008

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NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


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Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


lowmolecular weight oligomers An exception is the reactionwith sulfuric acid homogeneous catalyst which yields rela-tively high molecular weight polyglycerols [14] A previousstudy on themorphology of glycerol etherification derivativesconducted with 13C NMR reported carbon assignments forlinear branched and cyclic structures [17] Results of polyg-lycerol 13C NMR spectroscopy showed that homogeneousacid-catalyzed polymerization of glycerol at high tempera-tures favors the occurrence of branched structures [14] Toour knowledge there are no previous reports on the effect ofcatalyst concentration on polyglycerolmorphology producedfrom glycerol or on the combined effect of temperature andcatalyst concentration on polyglycerol properties

In this work polyglycerol is obtained from glycerol bya step-growth polymerization reaction using sulfuric acidas catalyst The effect of tuning temperature and catalystconcentration during synthesis conditions on the parame-ters that affect polyglycerol morphology hydroxyl numbermolecular weight polydispersity functionality and thermalproperties were studied Our goal is to provide guidelinesfor the polyglycerol synthesis from glycerol yielding specificproduct characteristics by varying temperature and catalystconcentration during synthesis The experimental strategyperformed in this study was based on a combinatorialexperiment with temperature and catalyst concentration ofsynthesis as factors This approach allows considering possi-ble interactions between factorsThe techniques used includematrix-assisted laser desorption and ionization time-of-flightspectrometry (MALDI-TOF) nuclear magnetic resonancespectroscopy (NMR) and differential scanning calorimetryanalysis (DSC) This paper is organized as follows firstmaterials reaction procedure and polymer characterizationtechniques are described second results of infrared spec-troscopic analysis (FT-IR) of synthesized polyglycerol fromglycerol are discussed and third the analysis of resultsis presented Finally conclusions of the main findings arereported

2 Experimental

21 Materials Materials used for the synthesis were obtainedfrom different vendors glycerol (85) sulfuric acid (95)phenolphthalein indicator and sodium hydroxide (99)were purchased from Merck acetic anhydride was obtainedfrom Carlo Erba and pyridine (95) fromMallinckrodt

22 Reaction Procedure Polymerization reactions were car-ried out in 50mL closed glass reactor in an inert envi-ronment (nitrogen atmosphere) Water was continuouslyremoved from the reaction mixture with a vacuum pumpGlycerol (20mL) polymerization reaction temperature wasvaried from 130∘C to 170∘C with a heating bath controlCatalyst concentrationwasmodified from 15 (ww) to 52(ww) All the reactions were carried out at 24 inches ofHg Polymerization products were neutralized with a NaOH01N solution and dried at 80∘C for 24 h without furtherpurification process

23 Polymer Characterization Polymerization reaction pro-ducts were analyzed using Fourier transform infrared spec-troscopy (FTIR) to identify functional groups Infraredspectra were obtained in transmittance mode in a ThermoScientific Spectrometer (Nicolet 1550 FT-IR)

Hydroxyl numbers were calculated following the ASTMD 4274-11 method Polymer samples were acetylated withan acetic anhydride-pyridine solution The unreacted acety-lation reagent was hydrolyzed with water and the aceticacid titrated with 05N sodium hydroxide solution Thehydroxyl content was calculated from the difference intitration between the acetic anhydride-pyridine solution usedas a blank and sample solutions

Molecular weight distributions of different reaction prod-ucts were obtained using MALDI-TOF-MS measurementsperformedwith a Bruker Reflexmass spectrometer equippedwith a nitrogen laser delivering 3 ns laser pulses at 337 nmRecrystallized 120572-cyano-4-hydroxycinnamic acid (10mgmL)in 30 70 (vv) acetonitrilewater containing 01 (vv)trifluoroacetic acid (TFA) was used as the matrix Sodiumchloride solution was used as cationization agent Polymersamples were dissolved in water to a final concentration of10 120583gmL An aliquot of the matrix (08 120583L) was applied toa multistage target until solvent evaporation subsequently01 120583L of cationization agent and 02120583L of sample were added

Polymer morphology analyses were performed using 13CNMR quantitative spectra taken on a Bruker Ultrashield400MHz (Avance III 400)TheDistortionless Enhancementby Polarization Transfer (DEPT) techniquewas used to deter-mine peaksmultiplicity Samples were prepared by dissolvingthe polymer in deuterated water to a final concentration of250 gL

Glass transition temperatures were obtained using Dif-ferential Scanning Calorimetry (DSC)measurements carriedout on a DSC Discovery TA Instruments Inc (USA) Sam-ples were subjected to two heating scans with the followingtemperature program first heating scan from minus80 to 200∘C ata heating rate of 5∘Cmin subsequently cooling to minus90∘C ata heating rate of 10∘Cmin and finally a second heating scanfrom minus90∘C to 400∘C at a heating rate of 5∘Cmin All scanswere performed under nitrogen purge gas of 50mLmin

3 Results and Discussion

The analysis of results was statistically supported using acombinatorial experimental design with temperature andcatalyst concentration as factors Each factor was evaluatedat three different levels that is temperatures of 130∘C 150∘Cand 170∘C and catalyst concentrations of 15 (ww) 335(ww) and 52 (ww) The response variables to ana-lyze were polyglycerol hydroxyl number molecular weightand polydispersity To determine polyglycerol morphologyand thermal properties a second experimental design wasperformed This time the factors were evaluated at twodifferent levels of temperature 130∘C and 150∘C and catalystconcentrations 15 (ww) and 52 (ww) Experimentaltest sequences were randomized and three replicates per levelwere taken





O-H C-H C-O

Tran

smitt

ance

() Catalyst 52 (ww)

Catalyst 15 (ww)

4000 3500 3000 2500 2000 10001500

Temperature 130∘C

Temperature 170∘C





15

335

52130150

170200

300

400

500

600

700

Hyd

roxy

l num

ber (

mg

KOH

g)

Temperature ( ∘C)


) (ww)







Catalyst 15 (ww)

2400 2600 2800 3000 3200 3400 3600 3800mz

Temperature 130∘C

(a)

2400 2600 2800 3000 3200 3400 3600 3800

Catalyst 52 (ww)

mz

Temperature 170∘C

(b)








130 15 29872 29191 1023130 335 29865 29176 1024130 52 29762 29089 1023150 15 29782 29103 1023150 335 29783 29113 1023150 52 30124 29432 1023170 15 29911 29245 1023170 335 29756 29082 1023170 52 29825 29172 1022


2OH carbons


2-O-






Temperature(∘C)

Catalyst (ww)

-CH2OH carbons


()



hydroxyl groups()


()




2-O- -CH-O-







C-251015840 and C-231015840

C-10 C-12 C-20 andC-22

HO O

OH

O

HO

OO

HO

O

OH

HO

OH

OO

O

O

O

OHOH

O OHHO

1

2

3

4

5

6

7

8

9

1011

12

1314

15

16

1718

1920

2122

23 24 2526

27

15

9998400

1699840016998400

19998400

1799840017998400

14998400

1399840018998400

1599840025998400

24998400

23998400

26998400

27998400

Scheme 1


Catalyst 15 (ww)


Branching

-CH-O- -CHOH-


Polyetherchains

-CH2-O- -CH2OH

Temperature 130∘C 800070006000500040003000200010000

81 80 79787776757473727170696867666564636261605958

f1 (ppm)





03

02

01

00

minus01

minus02

minus03

minus04

minus05

minus06

minus90

minus70

minus50

minus30

minus10 10 30

50

70

90

110

130

150

170

190

210

230

250

2

2

3

3

3

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)

PG 15 (ww)-150∘C

Second heating scan

First heating scan

1

1

(a)

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)


PG 15 (ww)-130∘C

PG 15 (ww)-150∘C

PG 52 (ww)-130∘C

PG 52 (ww)-150∘C

(b)









4 Conclusions




Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







O-H C-H C-O

Tran

smitt

ance

() Catalyst 52 (ww)

Catalyst 15 (ww)

4000 3500 3000 2500 2000 10001500

Temperature 130∘C

Temperature 170∘C





15

335

52130150

170200

300

400

500

600

700

Hyd

roxy

l num

ber (

mg

KOH

g)

Temperature ( ∘C)


) (ww)







Catalyst 15 (ww)

2400 2600 2800 3000 3200 3400 3600 3800mz

Temperature 130∘C

(a)

2400 2600 2800 3000 3200 3400 3600 3800

Catalyst 52 (ww)

mz

Temperature 170∘C

(b)








130 15 29872 29191 1023130 335 29865 29176 1024130 52 29762 29089 1023150 15 29782 29103 1023150 335 29783 29113 1023150 52 30124 29432 1023170 15 29911 29245 1023170 335 29756 29082 1023170 52 29825 29172 1022


2OH carbons


2-O-






Temperature(∘C)

Catalyst (ww)

-CH2OH carbons


()



hydroxyl groups()


()




2-O- -CH-O-







C-251015840 and C-231015840

C-10 C-12 C-20 andC-22

HO O

OH

O

HO

OO

HO

O

OH

HO

OH

OO

O

O

O

OHOH

O OHHO

1

2

3

4

5

6

7

8

9

1011

12

1314

15

16

1718

1920

2122

23 24 2526

27

15

9998400

1699840016998400

19998400

1799840017998400

14998400

1399840018998400

1599840025998400

24998400

23998400

26998400

27998400

Scheme 1


Catalyst 15 (ww)


Branching

-CH-O- -CHOH-


Polyetherchains

-CH2-O- -CH2OH

Temperature 130∘C 800070006000500040003000200010000

81 80 79787776757473727170696867666564636261605958

f1 (ppm)





03

02

01

00

minus01

minus02

minus03

minus04

minus05

minus06

minus90

minus70

minus50

minus30

minus10 10 30

50

70

90

110

130

150

170

190

210

230

250

2

2

3

3

3

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)

PG 15 (ww)-150∘C

Second heating scan

First heating scan

1

1

(a)

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)


PG 15 (ww)-130∘C

PG 15 (ww)-150∘C

PG 52 (ww)-130∘C

PG 52 (ww)-150∘C

(b)









4 Conclusions




Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Catalyst 15 (ww)

2400 2600 2800 3000 3200 3400 3600 3800mz

Temperature 130∘C

(a)

2400 2600 2800 3000 3200 3400 3600 3800

Catalyst 52 (ww)

mz

Temperature 170∘C

(b)








130 15 29872 29191 1023130 335 29865 29176 1024130 52 29762 29089 1023150 15 29782 29103 1023150 335 29783 29113 1023150 52 30124 29432 1023170 15 29911 29245 1023170 335 29756 29082 1023170 52 29825 29172 1022


2OH carbons


2-O-






Temperature(∘C)

Catalyst (ww)

-CH2OH carbons


()



hydroxyl groups()


()




2-O- -CH-O-







C-251015840 and C-231015840

C-10 C-12 C-20 andC-22

HO O

OH

O

HO

OO

HO

O

OH

HO

OH

OO

O

O

O

OHOH

O OHHO

1

2

3

4

5

6

7

8

9

1011

12

1314

15

16

1718

1920

2122

23 24 2526

27

15

9998400

1699840016998400

19998400

1799840017998400

14998400

1399840018998400

1599840025998400

24998400

23998400

26998400

27998400

Scheme 1


Catalyst 15 (ww)


Branching

-CH-O- -CHOH-


Polyetherchains

-CH2-O- -CH2OH

Temperature 130∘C 800070006000500040003000200010000

81 80 79787776757473727170696867666564636261605958

f1 (ppm)





03

02

01

00

minus01

minus02

minus03

minus04

minus05

minus06

minus90

minus70

minus50

minus30

minus10 10 30

50

70

90

110

130

150

170

190

210

230

250

2

2

3

3

3

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)

PG 15 (ww)-150∘C

Second heating scan

First heating scan

1

1

(a)

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)


PG 15 (ww)-130∘C

PG 15 (ww)-150∘C

PG 52 (ww)-130∘C

PG 52 (ww)-150∘C

(b)









4 Conclusions




Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





Temperature(∘C)

Catalyst (ww)

-CH2OH carbons


()



hydroxyl groups()


()




2-O- -CH-O-







C-251015840 and C-231015840

C-10 C-12 C-20 andC-22

HO O

OH

O

HO

OO

HO

O

OH

HO

OH

OO

O

O

O

OHOH

O OHHO

1

2

3

4

5

6

7

8

9

1011

12

1314

15

16

1718

1920

2122

23 24 2526

27

15

9998400

1699840016998400

19998400

1799840017998400

14998400

1399840018998400

1599840025998400

24998400

23998400

26998400

27998400

Scheme 1


Catalyst 15 (ww)


Branching

-CH-O- -CHOH-


Polyetherchains

-CH2-O- -CH2OH

Temperature 130∘C 800070006000500040003000200010000

81 80 79787776757473727170696867666564636261605958

f1 (ppm)





03

02

01

00

minus01

minus02

minus03

minus04

minus05

minus06

minus90

minus70

minus50

minus30

minus10 10 30

50

70

90

110

130

150

170

190

210

230

250

2

2

3

3

3

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)

PG 15 (ww)-150∘C

Second heating scan

First heating scan

1

1

(a)

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)


PG 15 (ww)-130∘C

PG 15 (ww)-150∘C

PG 52 (ww)-130∘C

PG 52 (ww)-150∘C

(b)









4 Conclusions




Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




03

02

01

00

minus01

minus02

minus03

minus04

minus05

minus06

minus90

minus70

minus50

minus30

minus10 10 30

50

70

90

110

130

150

170

190

210

230

250

2

2

3

3

3

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)

PG 15 (ww)-150∘C

Second heating scan

First heating scan

1

1

(a)

Temperature (∘C)

Hea

t flow

nor

mal

ized

(Wg

)


PG 15 (ww)-130∘C

PG 15 (ww)-150∘C

PG 52 (ww)-130∘C

PG 52 (ww)-150∘C

(b)









4 Conclusions




Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




4 Conclusions




Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials














CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article effect of temperature and catalyst concentration...

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