high solids solution acrylics: controlled architecture

High solids solution acrylics: Controlled architecture hybrid cross-

linking pressure sensitive adhesives

Christopher L. Lester, Ph.D. Performance Adhesive Center, Avery Dennison

William L. Bottorf, Performance Adhesive Center, Avery Dennison

Kyle R. Heimbach, Performance Adhesive Center, Avery Dennison

Abstract

As a continuation of work reported at the 2009 PSTC Technical Seminar we report herein

the synthesis of acrylic polymers with controlled molecular weight, architecture and

placement of reactive functional groups. In particular, acrylic polymers useful as

pressure sensitive adhesives are described that utilize hybrid cross-linking technology.

The hybrid cross-linking technology described is acid metal chelate used in conjunction

with alkoxysilane sol-gel reactions. The influence of type, amount, and placement of

alkoxy-silane functionalities on viscoelastic properties and corresponding pressure

sensitive adhesive attributes are discussed. Additionally, hybrid cross-linking, controlled

architecture pressure sensitive adhesives are reported with varying glass transition

temperature and solubility parameter. The novel controlled architecture acrylic polymers

allow for the development of high solids solution adhesives at low viscosities and 100%

solids warm melt compositions with processable rheology. Furthermore, the controlled

architectured polymers display enhancements in adhesive performance relative to random

copolymers of the same composition.

Introduction

Polymer architecture and micro-structure have been shown historically to

dramatically influence material and, in particular, adhesive properties. Control of acrylic

polymer architecture and micro-structure has largely consisted of modulating molecular

weight and branching through polymerization temperature, initiator type, and in-process

monomer concentration. Also, some ability to modulate composition spatially along the

polymer chain could be afforded via selection of monomers with reactivity ratios

different from the primary backbone monomers.

While a considerable span of adhesive performance can be attained with the

aforementioned methods, much finer controls are possible with different polymerization

techniques. Controlling polymer architecture in a finer sense has been a subject of

significant research over the past fifty years. It has been demonstrated widely in the

literature that exerting finer control over the polymer architecture results in different and

often enhanced adhesive performance. In some cases, countercurrent properties can often

be decoupled. Previously reported architectures include block copolymers, telechelic

polymers, and random polymers of controlled molecular weight. While, the

aforementioned architectures all provide unique properties, they also have disadvantages.

Random copolymers either require high molecular weight to attain certain

balances of properties or require high degrees of cross-linking which can yield a poor

balance of properties. Telechelic polymers by definition have reactive functional groups

placed exactly at the end-groups and nowhere else in the backbone. The functional

groups then serve solely to increase linear molecular weight and/or form networks in

which free polymer chain ends are eliminated. Telechelic polymers consequently yield

high strength elastomeric materials but lack the viscous liquid character critical to

pressure sensitive adhesive (PSA) performance and require further formulation for

good PSA characteristics. Phase separated block copolymers when formulated

appropriately are known to yield a wide range of adhesive performances. However, due

to the nature of the physical cross-links in phase separated systems the thermal and

solvent resistance can be poor.

In approximately the last 20 years, a variety of pseudo-living or controlled radical

polymerization techniques have been developed to afford good architectural control of

(meth)acrylic monomers. These techniques are more tolerant to a wider variety of

functional groups when compared to living anionic, cationic, and catalytic techniques. A

substantial amount of fundamental research has been performed to understand these types

of polymerization and a thorough review has been edited by Matyjewski.1 Reversible

Addition Fragmentation chain Transfer (RAFT) polymerization is one such technique

that has been shown to work exceedingly well with a wide variety of (meth)acrylic

monomers yielding excellent control of molecular weight and polydispersity.2 The

RAFT mechanism for controlled polymerization is well understood and reported

extensively.1-3

It was previously reported at the 2009 PSTC Technical Seminar that controlled

placement of cross-linkable functional groups could be readily afforded by controlled

radical polymerization.4 These novel polymers allowed for the ability to synthesize

polymers to be of modest to low molecular weight and correspondingly to display low

solution viscosities at high solids content and to also display low viscosities in the melt.

In addition to the desirable solution and melt properties, it was found that the

performance of the resulting adhesives was comparable to high molecular weight

controls and in some cases the adhesive performance was markedly improved.

This study details the synthesis of controlled architecture acrylic polymers with

controlled placement of reactive alkoxy-silane functionalities. These types of polymers

are described as hybrid cross-linking pressure sensitive adhesives. The influence of the

type and amount of alkoxy-silane monomers is described with regards to visco-elastic

properties and corresponding pressure sensitive adhesive performance. Formulated

systems using the hybrid cross-linked materials are described as well as polymers in

which the glass transition and solubility parameter have been varied to modulate

performance.

Experimental

Base acrylic esters such as 2-Ethylhexyl Acrylate (EHA), Butyl Acrylate (BA),

Acrylic Acid (AA) and Isobornyl Acrylate (IBOA) were obtained from various

commercial suppliers and used as received. Methacryloxypropyl Tri-methoxysilane

(MPtMS) and Methacryloxymethyl Tri-ethoxysilane (MMtES) were all obtained from

Wacker Chemical and used as is. Dibenzyl trithiocarbonate (DBTTC) was obtained from

Arkema France and used as received and is shown in Scheme 1. Also in Scheme 1 is a

depiction of how

monomers are incorporated upon sequential addition. All of the polymerizations were

initiated with Azobis(isobutyronitrile) (AIBN). The polymers were all made in organic

solvents, most typically Ethyl Acetate. Unless otherwise stated all of the polymers were

formulated with aluminum acetoacetonate (AAA) at 0.5% by weight based on polymer

solids. All samples were coated at approximately 2.0 mil adhesive thickness onto 2.0mil

mylar. The coatings were all air dried for 10 minutes and placed in a forced air oven for

Scheme 1. Chemical structure of dibenzyl trithiocarbonate (DBTTC) and polymers after a single monomer addition followed by a subsequent monomer addition.

5 minutes at 130oC and closed with 100% solids platinum cured silicone paper liner.

The laminates were all aged in a controlled climate room for 24 hours prior to testing.

Molecular weights were measured using a Polymer Standards Services GPC

outfitted with a refractive index detector and calibrated using polystyrene standards.

Solution viscosities were measured using a Brookfield RVT viscometer. Spindle and

spindle speeds were selected such that a torque value of 40-80% was achieved for

optimal accuracy. Dynamic mechanical analysis (DMA) was performed on a TA

Instrument AR-1000 rheometer using parallel plate clamps. 1.0mm thick samples were

placed in the clamp and annealed at 75oC for 10 minutes to ensure good adhesion. The

samples were then cooled to -80oC for 10 minutes and ramped at 3

oC per minute up to

150oC. During the temperature ramp the sample was oscillated at a frequency of 10

rad/s. Unless otherwise noted, the following test methods were used for evaluating the

adhesive properties of the acrylic polymers.

PSA PERFORMANCE TEST METHODS

Test Condition 180° Peel a, b, 15 Minute Dwell 72 Hour Dwell Shear Strength c Shear Adhesion Failure Temp.(SAFT) d

(a) Peel, sample applied to a stainless steel panel with a 5 pound roller with 1 pass in

each direction. Samples conditioned and tested at 23°C.

(b) Peel, sample applied to a high-density polyethylene or polypropylene panel with a

5 pound roller with 5 passes in each direction. Samples conditioned and tested at

23°C.

(c) Shear: 1 kg weight with a 1/2 inch by 1/2 inch overlap. Sample applied to a

stainless steel panel with a 10 pound roller with 5 passes in each direction.

Samples conditioned and tested at 23°C.

(d) SAFT: 1000 gram weight, 1 inch by 1 inch overlap (2.2 pounds/square inch).

Sample applied to a stainless steel panel with a 10 pound roller with 5 passes in

each direction. Samples conditioned for 1 hour at 23°C and 15 minutes at 40°C.

Temperature increased by 0.5°C/min. until failure.

Results and Discussion

Scheme 2 depicts polymer architectures that are possible through the use

a.

b.

c.

Scheme 2. Varying RAFT/DBTTC mediated architectures including: a.

Random, b. end functional acid, and c. end functional alkoxy-silane.

of well controlled RAFT polymerizations. These architectures were reported previously,

but briefly it was found that segregating the cross-linkable functionalities such as

carboxylic acids or alkoxysilane moities can afford dramatically different material

properties that can be very desirable for pressure sensitive adhesives.4,5

In particular it

has been shown that low molecular weight architectured polymers are advantageous for

processing in that they can be at high concentrations in organic solvents at a low viscosity

or even melt processable in the absence of solvent. In addition to being advantageous for

processing, the low molecular weight architectured polymers were found to yield

pressure sensitive adhesive performance comparable to high molecular weight low solids

analogues. It was also previously reported that placing cross-linkable sites that react

O OH

O OH

O OHO OH

O OH

O OH

O OH

O OH

S

SS

O OHO OH

O OHO OH

O OH

O OHO OH

O OH

S

SS

S

SS

Alkoxy- Silane

Alkoxy- Silane

Alkoxy- Silane

independently from other cross-linkable functional groups can provide significant

performance enhancements in addition to having enhanced processability through lower

molecular weight. This type of system is shown in Scheme 3 in which alkoxy-silane

groups are positioned in the end regions of a

pressure sensitive adhesive acid containing random copolymer. This polymer can be

cross-linked with AAA which also serves as a Lewis acid catalyst for the sol-gel

condensation reaction of the alkoxy-silane moieties. This type of material was previously

compared to a commercial random copolymer of the same composition. To expand on

this work, additional copolymer controls were made and characterized. In all cases,

identical copolymer compositions consisting of 2-EHA, BA and acrylic acid were used

and the architecture and presence of alkoxy silane monomers was varied. Table 1 details

the various polymers molecular weight, solids, and solution viscosities. All of the RAFT

derived materials exhibit similar measured molecular weights with narrow

polydispersities which is indicative of a well controlled polymerization. As a result of

the molecular weights being fairly low, the solids and viscosities of these polymers are all

Scheme 3. Depiction of Hybrid-crosslinked RAFT derived architectured PSA.

O OH

O OH

O OHO OH

O OH

O OH

O OH

O OH

S

SS

Alkoxy- Silane Alkoxy-

Silane

Si

OCH3

OCH3

OCH3

Water

Lewis acid2 Si

OCH3

OCH3

O Si

OCH3

OCH3

+ CH3O

>67.0% and less than 14,000 cps. The commercial controls are higher in molecular

weight with broad polydisperities and correspondingly display

lower solids contents to be at a reasonable viscosity. Figure 1 is a plot of storage

modulus as a function of temperature for the different polymers described in Table 1. All

of the polymers exhibit identical glass transition temperatures (Tg) because of the

identical base compositions. However, at temperatures above

the Tg there are marked differences between the materials. The RAFT polymer with

MPtMS displays a very flat plateau modulus while the RAFT copolymer

without MPtMS does not to the extent that the material actually displays some flow

Table 1

51 EHA 45 BA 4 AA

Type RAFT Architectured

RAFT Random

Commercial Control

Commercial Control

MPtMS Y N Y N

Mn 80,060 81040 63519 61,531

Mw 127,540 122360 366140 380,961

PDI 1.6 1.51 5.76 6.2

Solids 69.0 69.0 51.5 50.0

Solution Viscosity

14,000cps 11600cps 4700cps 5,000cps

-100.0 -50.0 0 50.0 100. 150.0 200.0 Temperature (°C)

1000

10000

1.000E5

1.000E6

1.000E7

1.000E8

1.000E9

1.000E10

G' (dyne/cm^2)

RAFT with MPtMS RAFT no MPtMS Commerical with MPtMS Commerical no MPtMS

Figure 1. Storage modulus as a function of temperature for EHA/BA/AA copolymers of varying architecture and MPtMS amount.

characteristics at elevated temperature. The commercial control without MPtMS displays

similar behavior to that of the silane-free RAFT polymer but with overall higher modulus

as a function of temperature which results from the materials higher molecular weight.

When adding an equivalent amount of MPtMS, the commercial control displays a flat

plateau modulus but with overall higher values than the RAFT polymer containing

MPtMS. The pressure sensitive adhesive performance is very reflective of the DMA data

as can be seen in Table 2. For example, the RAFT copolymer containing alkoxy-silane

monomer exhibits

what could be characterized as the best overall balance of PSA performance. It displays

high ultimate adhesion to stainless steel, moderate adhesion to polypropylene, with

relatively high shear values and >200oC SAFT. The RAFT copolymer without alkoxy-

silane is a low cohesive strength material that displays significant cohesive failures in

peel adhesion coupled with low shear and SAFT values. The commercial control without

alkoxy-silane was better performing than the RAFT analogue in that it displayed high

adhesion values but it still displayed lower shear and SAFT values. The commercial

control with alkoxy-silane is a high cohesive material in that it has high SAFT values and

shears that did not fail cohesively but did not display the high adhesion values of the

RAFT copolymer containing alkoxy-silane. This is a result of the random incorporation

Table 2 51 EHA 45 BA 4 AA

Type RAFT RAFT Commercial Control

Commercial Control

MPtMS Y N Y N

180o Peel to

Stainless Steel 15 min Dwell (Lbs/in)

3.5 5.19 cohesive

2.72 3.8

180o Peel to

Stainless Steel 72 hr Dwell (Lbs/in)

8.4 cohesive

5.58 cohesive

4.63 7.5

180o Peel to

Polypropylene Lbs/in)

2.35 2.54 cohesive

2.00 1.20

SAFT, 1kg/Sq. In (Failure Temp

oC)

>200 66 >200 90

Shear, 2kg/ Sq. In (Failure Time, Mins)

135.1 adhesive

17.0 41.0 adhesive

41.0

of the MPtMS in the polymer back-bone which would produce lower molecular weight

between cross-links that yields an overall higher modulus. Also it is important to note

that even if there were equivalent performance between the RAFT and commercial

control analogues there would still remain the processing advantage of the RAFT

materials afforded by high solids at coatable viscosities.

It is important to note that the coating and drying conditions for MPtMS

containing polymers were 10 minutes at 130oC in a forced air oven in order to ensure

complete cure. While it is possible to reach these kinds of conditions in some coating

assets it may be difficult in others. Additionally, when coating thermally-sensitive

substrates the high temperatures may present difficulties. Scheme 4 displays various

alkoxy-silane methacrylate monomers and relative

propyl analogues. Shown in Figure 2 is a plot of Williams Plasticity Index (WPI) as a

function of temperature for MPtMS and MMtES containing pressure sensitive adhesives.

The MPtMS containing PSA exhibits substantially lower plasticities at all temperatures

when compared to the MMtES containing PSAs. The MMtES exhibits higher plasticities

and of note is the flatter response to

Increasing Reactivity

a.

b.

Scheme 4. Reactivity of varying alkoxy-silane monomers:

a. Methacryloxypropyltrimethoxysilane (MPtMS), b. Methacryloxymethyl

triethoxysilane (MMtES)

temperature over the MPtMS materials. Figure 3 is a plot of storage modulus as a

function of temperature for the PSAs with varying alkoxy-silane types and one can see

that the materials when fully cured are remarkably similar. The similar rheology is

1.5

2

2.5

3

3.5

4

4.5

5

90 100 110 120 130 140 150

Temp (oC)

Willia

ms

Pla

sti

cit

y In

de

x

MPtMS

MMtMS

Figure 2. Williams Plasticity as a function of drying temperature for varying alkoxy-

silane monomer.

manifested in the PSA performance displayed in Table 3 with the

-100.0 -50.0 0 50.0 100.0 150.0 200.0temperature (° C)

10000

1.000E 5

1.000E 6

1.000E 7

1.000E 8

1.000E 9

G' (

Pa)

DE V -8670ADE V -8670A New S ilane

MPtMS MMtES

Figure 3. Storage modulus as a function of temperature for EHA/BA/AA RAFT

polymers with varying alkoxy-silane monomers.

primary difference observed in slightly lower peel performance of the MMtES containing

PSA which is attributable to a slightly higher modulus resulting in mixed

adhesive/cohesive failure modes. This difference in peel can be modulated in a variety of

ways including varying the MMtES content as well as varying AAA cross-linker level in

the same fashion one would modify a standard solution acrylic.

In order to demonstrate how to tune the performance of these types of PSAs, a

series of RAFT polymers was made of the same composition described previously in

which the statistical number of MMtES was varied from 0.5-2.5 per end region. The

molecular weights and physical characteristics of the wet adhesives are shown in Table 4.

The molecular weights and polydispersities are all approximately the same.

Correspondingly, the solids and solution viscosities are similar in that they are all >68%

and <15000cps. It should be noted that at higher levels of MMtES some increase in

polydispersity occurred which resulted in higher viscosities. The higher polydispersity

and corresponding increase in viscosity is likely due to some reaction of the MMtES

during the polymerization. Figure 4 is a plot of storage modulus as a function of MMtES

monomers per chain end. All of the samples display the same glass transition

temperature that

Table 3 51 EHA 45 BA 4 AA

Type MPtMS MMtES

180o Peel to Stainless

Steel 15 min Dwell (Lbs/in)

3.5 3.4

180o Peel to Stainless

Steel 72 hr Dwell (Lbs/in)

8.4 cohesive

7.05 mixed

180o Peel to

Polypropylene Lbs/in) 2.35 2.53


oC)

>200 >200

Shear, 1kg/0.25 Sq. In (Failure Time, Mins)

120 adhesive

135 adhesive

one would expect from polymers of the same composition but differ markedly in the

rubbery plateau. In every case the rubbery plateau is extremely flat with the modulus

increasing as the number of MMtES monomers increases. Interestingly, upon raising the

MMtES level from 2 to 2.5 per end region the modulus stays the same. This means that

there are very few unfunctionalized chain ends. The

Table 4

RAFT Architectured 51EHA/45BA/4AA

# MMtES 0.5 1 1.5 2 2.5

Mn 77100 80100 78200 75100 71600

Mw 131300 127540

149600 145500 159200

PDI 1.70 1.6 1.9 1.9 2.2

Solids 68.4 69.0 68.3 68.4 68.0

Viscosity 12200 12500 14800 15200 22000

-75.0 -50.0 -25.0 0 25.0 50.0 75.0 100.0 125.0 150.0 175.0temperature (°C)

10000

1.000E5

1.000E6

1.000E7

1.000E8

1.000E9

1.000E10

G'

(dy

ne

/cm

^2

)

0.51.01.52.02.5

Figure 4. Storage modulus as a function of temperature for EHA/BA/AA RAFT

polymers with varying amount of MMtES per polymer end region.

dramatic difference in rheology can be observed in the pressure sensitive adhesive

performance. Table 5 displays broad range of adhesive performance can be attained by

modulating the theoretical number of MMtES per chain. For

Example, at lower levels of MMtES the adhesives exhibit permanent PSA performance

profiles in that the materials are very high in peel adhesion with cohesive failures. In

particular, the 0.5 MMtES per end material displays permanent adhesive performance but

is accompanied by lower shear and SAFT values. The increase to 1.0 MMtES per end

yielded lower initial peel values but higher ultimate peels with greatly enhanced shear

and SAFTs. Further increasing the MMtES level then results in reductions in peel

performance and higher cohesive strength materials as evidenced by higher shear values.

It is important to note that the shear values are not dramatically higher for samples with

higher MMtES levels but this is due not to a lack of cohesive strength but from a shift in

failure mode from cohesive to adhesive. Ultimately, at the highest levels of MMtES one

can observe performance that is characteristic of removable adhesives.

Table 5

51 EHA 45 BA 4 AA

# MMtMS 0.5 1 1.5 2 2.5

180o Peel to


6.5 cohesive

3.4 2.25 1.84 1.52

180o Peel to


6.6 cohesive

7.05 mixed

4.00 3.21 2.52

180o Peel to

Polypropylene (Lbs/in)

0.5 zip 2.53 1.65 1.50 0.80


oC)

115

>200 >200 >200 >200


65 cohesive

135 Mixed

155 Mixed

224 Adhesive

195 Adhesive

The high cohesive strength of the higher MMtES levels would lend itself to

formulation with tackifiers. In Figure 5, storage modulus as a function of temperature is

plotted for the 2 MMtES polymer that has been tackified with two levels of a

hydrogenated rosin ester. A classic tackifier response is observed in that the glass

transition temperature has been increased with an accompanying lowering of plateau

modulus. Naturally the magnitude of change in the rheology

is a direct function of level of tackier. The PSA performance of the formulated adhesives

is shown in Table 6. As one would expect the peel adhesions of the tackified systems are

substantially higher relative to the unformulated base polymer. In particular the adhesion

to olefin substrates with polypropylene used as an example is dramatically improved. In

addition to the greatly enhanced peel adhesions what is remarkable to note is that the

materials exhibit excellent shear values that is a result of the high cohesive strength of the

base polymer.

-75.0 -50.0 -25.0 0 25.0 50.0 75.0 100.0 125.0 150.0 175.0temperature (°C)

10000

1.000E5

1.000E6

1.000E7

1.000E8

1.000E9

1.000E10

G'

(dy

ne

/cm

^2

)

0%20%40%

Figure 5. Storage modulus as a function of temperature for EHA/BA/AA polymer

with 2 MMtES per end with varying level of rosin ester tackifier.

In order to modulate adhesion of these systems on various substrates without the

use of tackifiers one common approach is to use Tg modifying monomers and in

particular monomers that are lower in solubility parameter. In this case polymers are

made of the architecture described previously but are varied in composition to yield a

copolymers with a calculated Fox Tgs of -50 oC and -40

oC. In this circumstance the

polymer composition was primarily 2-EHA with the high Tg low solubility parameter

monomer IBOA being used. In this case, 0.5 MMtES per end was utilized in order to

generate materials that would be permanent high peel adhesives. These materials are

directly comparable to the EHA BA copolymer with 0.5 MMtES per end described

previously. Table 7 displays the ultimate peel adhesions of these materials on stainless

steel and a variety of plastic substrates. The control material displayed moderately high

peels on stainless steel and the more polar plastics with relatively low shear. When the

Tg is increased to -50oC very high peels are observed on stainless steel and the polar

plastics in some cases peel adhesions close to 10 lbs/in are observed. The moderate Tg

material also displayed a significant enhancement

Table 6

51EHA/45BA/4AA

% Tackifier 0% 20% 40%

180o Peel to


1.84 3.00 9.23 cohesive

180o Peel to


3.21 3.70

9.74 cohesive

180o Peel to

HDPE (Lbs/in) 0.25 0.65 2.74

180o Peel to

Polypropylene (Lbs/in)

1.50 2.91 8.97 cohesive


oC)

>200 >200 103


224 adhesive

597 mixed

519.3 cohesive

in peel adhesion on lower surface energy plastics relative to the low Tg control.

Additionally, it is important to note that the -50oC material displayed higher shear than

the control. The higher Tg material exhibited moderate peel adhesion on stainless steel

and polar plastics with higher shear. On the low surface energy surfaces, the material

exhibited low bond strength with zippy or slipstick failure modes. This data indicates

that the higher Tg yielded a higher modulus material that had more difficulty wetting low

polarity surfaces. This can be considered a typical response with a simple increase in Tg

of a pressure sensitive adhesive system.

This paper has detailed the influence of concentration of alkoxy-silane

functionalities in a hybrid cross-linked high solids solution acrylic pressure sensitive

system. Specifically, it has been shown that the use of alkoxy-silane functionalities in the

manner described yield pressure sensitive adhesives that maintain modulus over a wide

range of temperatures. The unique rheology of the pressure sensitive adhesives yields

good performance with regards to balance of adhesion and cohesion as well as excellent

temperature resistance. It has been found that increases in the number of alkoxy-silanes

per polymer end region modulate the absolute value of the plateau modulus in a dramatic

fashion. The resulting change in modulus yields a wide range of pressure sensitive

adhesive performance from permanent to removable. Furthermore it has been shown that

Table 7

0.5 MMtES per chain end

Fox Tg (oC) -56 -50 -40

180o Peel to


6.35 cohesive

10.75 cohesive

4.95 mixed zipping

180o Peel to LDPE

72 hr Dwell (Lbs/in)

0.85 1.65 0.4 zipping

180o Peel to

HDPE 72 hr (Lbs/in)

0.4 0.85 0.4 zipping

180o Peel to PET

72 hr (Lbs/in) 6.2

cohesive

9.50 cohesive

2.38 zipping

180o Peel to ABS

72 hr (Lbs/in) 4.5

cohesive 9.84

cohesive 5.43


51 cohesive

145 cohesive

176 cohesive

these materials can serve as excellent formulating base polymers such that high adhesion

to plastics can be attained while maintaining high cohesive strength. Additionally, it has

been demonstrated that the architectures described can be used with a variety of

monomer compositions to afford varying desirable properties such as adhesion to low

surface energy substrates.

References

1. Matyjaszewski, K., Ed. ACS Symposium Series, Controlled

Radical Polymerization: Progress in ATRP, NMP and RAFT;

American Chemical Society: Washington DC, 2000; Vol. 768.

2. Le, T.P.; Moad, G.; Rizzardo, E.; Thang, S.H. Int. Patent Appl.

WO 9801478, 1998

3. Moad, G.; Solomon, D. H. The Chemistry of Free Radical

Polymerization; Elsevier: Amsterdam, 2006.

4. Lester, C. L.; Bottorf, W. L., PSTC Tech 32 2009

5. PCT application WO 2009/117654

high solids solution acrylics: controlled architecture

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