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Technical Report No. 9

Model Filled Polymers IX. Synlthesis of UniformlyCrosslinked Polystyrene Microbeads

by

Zheng-You Ding, Shenlmin Ma, Dennis Kriz, J. J. Aklonis* and R. Salovey

A ~ ewi ro/ -o

Prepared for Publication " !r)IC T,- 4]

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Journal of Polymer Science: Polymer Physics Ai1 bU1,y e

University of Southern CaliforniaDepartment of Chemical Engineering . _

*Department of ChemistryLos Angeles, California 90089-1211

June 10, 1991 w

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Technical Report No. 9

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I lIlLE (lIclulde se(vuly Cla iibca(iton)Model Filled Polymers IX. Synthesis of Uniformly Crosslinked Polystyrene Microbeads

12 IC[ItSOtJAL AU111011(S)Zheng-You Din,, Shenmin Ma, Dennis Kriz, J. J. Aklonis and R. Salovey

13a IYPE Or tPUFIT ill lIME COVERED I4 DAlE or REiOir (Year, Month, o.y) 115 'AGE COUNrTechi, ,al I ,IOM 9/1/90 iO 6/1/91 1991, June 10 24

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Submitted to Journal of Polymer Science: Polymer Physics

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FIEI D _G110.11 SIIU 6100t1Crosslinking; Polymeric Beads; Filled Polymers;Crossl.Lnk Density

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Monodisperse sized crosslinked polystyrene (PS) beads prepared by reaction of styrene (S) anddivinylbenzene (DVB), in batch emulsion copoiymerization in the absence of emulsifiers, are not uniformlycrosslinked, because DVB is more reactive than S. For copolymerization of 1 to 10 mole % DVB and S, withineach crosslinked PS microbead,7 the crosslink density varies by a factor exceeding two and decreases withincreased conversion. A semicontinuous copolymerization, involving incremental additions of DVB, producesuniformly crosslinked PS beads. For both copolymerization techniques, Tg correlates well with crosslink densityand PS beads are spherical and monodisperse in size.

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Model Filled Polymers IX. Synthesis of UniformlyCrosslinked Polystyrene Microbeads

Zheng-You Ding, Slenmii Ma, Dennis Kriz, J. J. Aklonis* and R. Salovey t

Departnmens of Cliemical Engineering and Chcmislry*University of Southern California

Los Aageles, CaliIrnia 90089-1211

ABSIRACT

Monodisperse sized crosslinked polystyrene (PS) beads prepared by reaction of styree

(S) and divinylbenzene (DVB), in batch emulsion copolymerization in the absence of cmulsitiers,

are not uniformly crosslioked, because DVB is more reactive than S. For copolymerization of I to

10 mole % DVB and S, within each crosslinked PS microbead, the crosslink density valies by a

factor exceeding two and decreases with increased conversion. A scmicontimmus

copolymerization, involving incremental additions of DVB, produces uniformly crossli ked PS

beads. For both copolymerization techmiqucs, T correlates well with crosslink dcesity and PS

bcads are spherical and monodispersc il size.

IT1o whom all coirespondence should be addiessed.

Model Filled Polymers IX. Synthesis of* UniformlyCosslinked Polystyrene Microbeads

Zheng-You Ding, Shenuin Ma, Dennis Kriz, J. J. Aklonis* and it. Saloveyt

Departnments of Chemical Engineering and Chemistry*University of Soulherni California

Los Angeles, California 90089-1211

INTRODUCTION

Crosslinkcd polystyrene (PS) is often prepared by the copolymerization of styrene (S)

monomcr with small amounts of divinylbenzene (DVB). In gencral, the composition of a

copolymer from binary copolymcrization dcpends on the composition and relative reactivity of

the monomers [1-31. As a result, the (instantancous) composition of a copolymer is, usually,

different from the composition of the monomer feed mixture, as one of the monomers may be

consumed more rapidly than the other. Ordinarily, the composition of' the monomr mixture,

varies, as the reaction proceeds, while the composition of the resulting copolymer, also, changes

with conversion. Only when the reactivity ratios in copolymerization ate both unity, or, for an

azeotiopic composition of monomers, will the copolymer and monomer compositions be

identical.

In order to characterize the crosslinked structure of copolymers of S and DV13, Wiley et

al. measured the reactivity ratios of S and DVB in binary copolyineiization, under various

conditions L4-101, and studied propei tics of tie coplymer 111-16]. Althutigh, lepoilted values of

the reactivity ratios were not completely consistent, results indicated tht DVB is itke ieactive

than S. This will result in depletion of DVB in the monomer mixture diiing copolyieialtion,

'o whomiIall olI Cu.;p"dPcice Should bed alddised.

2

before the S is consumed, and a drift in copolymier composition with conversion. As a result, it is

possible that crosslinkcd PS beads, prepared by batch emulsion copolymerization, may have

tightly crosslinkcd. cores, to which more lightly crosslinkcd or uncrosslinked PS chains arc

attached [4, 9]. Indecd, it has been suggested that emulsion polynierilzation occurs onl the surfaces

of growing particles [17] leading to inhomlopcncous polymerization, especially for large particle

sizes [18]. Small angle neutron scatterilg analyses of PS latex particles indicate that the particles

have a core-shell structure, with thle locus of polymerization at the particle surface Li19-211.

Using a recently reported technique of swelling ciosslinkcd polymieric beads onl anl

ultrafiltration miembrane [221, we directly examined the relationshil) between crossliink density

and reaction time, or conversion, in the synthesis of crosslinkcd PS beads. In addition, we

mcasured the glass transition teljperatures (T.i) of thec bcads by differential scanning calorimctry

(DSC). We also procccdcd to add DVI3 incremntially, during copolymerization, in order to

synthesize uniformly crossihikCel PS beads.

EXPERIMENTAL DET"IAILS

A. SYNTHESIS

1. Batch Copolyincrizatiozi

Crosslinked PS illicrobea(s were preparedI by emiulsion copolymneiizat ion in the absence

of emulsifier [23]. Commercial DVII obtained from Aldrich Chemical Comipany, was used as

crosslinker and consists of 551;o I)V1 isomiers, 42% ethylvinylbenzene and 3% diethylbeznei. IN

calculating tile composition of thie moinmer mixture, thle ctliylvinylbenzene was icluded withi S.

Polymerization was carried out in a 2 1 reactor innicised in a tlmermostat bati at 80 ± I C. Thle

concentration of the initiator, potassium persulfate, was 0.0014 miole/I in water. Every hour fr-om

thle onset of tile reaction, 10 nil aliquots of reaction mixture were rciio,'ed dur11ing L ontinlUous

agitation, caich placed in a 50 nil beaker, covered with alumlinuml foil, weighed, Opene1 d anld dried

in ain oven at 70-80*C for more tldIaii 15 hours. Partially dried samples were dried in a vacuum

oven at 70*C and -less than 1500 Pa pressure for 4 hours (to constant weight). Dried samples are

wcighecd and conversions calculated. Dried samples were used to measure crosslink densiy and

Ts.

2. Copolymeirization withi Successive Addition of DVII

Using a synuthesis micthod otherwise thle same its that for batch reaction, furthicr I)VI was

repeatedly added to the reactor. Thle initial corientration of %D VI for a (lesircd crosshink density

was selected by trial. Following thle conversion curve previously determined for batch

copolymerization, DNII would be added for every 10%1' of comononier consuimed in

polymerization. The concentration of DVB in thle monomer mixture, was continually calculated

and readjusted to its initial concentration by incremental addition of DVII. F'or experimental

convenience, at mixture of l)V1 and S was actually lidded.

A typical prcparation of 5 niol% crosslinked PS beads was carried out as followvs: 1450 ml

decionized water was added to a 2 1 reactor. The reactor was immersed in a thermnostat bath at 80)±

IT. Nitrogen was bubbled through thle water in the reactor while stirring at 400 rpm) for 30 muin,

to remove oxygen from thle system. Then, 113.27 g S and 6.73 g I)VI, wvhich had been washed

with at 10% aqueous sodium hydroxide solution and, then, deioiiizcd water for four times,

respectively, were added to thle recactor. IHere, thle initial concentration of DVII in thle monomer

mixture is 2.5 mol%. The rcactor was left for 20 minutes to attain thermal equilibrium. Then, 57 1

Ing initiator, p)otassiu~m persuilfatc, dissolved in 30 ml decionized water, was added and washed inuo

thle reactor with another 20 til decionized wvatr, and the polymerization began. The initial

concentration of initiator was 0.00 14 iiiol/l water. Nitrogen flow was continuied through~out the

reaction, at a lowv flow rate to minimize. evaporation. A mixture of DVII and S, in a weight ratio of

3:7, was added to thle reacting system according to Ttible 1.

The reaction wvas carried out for a total of 300 min. Beforeceach addition of DVI3, h0 ml

41

aliquots were removed from the reactor. Polymer samples were isolated and analyzed, as

previously described.

B. CROSSLINK DENSITY

The crosslink density of all samples was dctcrniincd by swclling on an ultraliltration

menmbrane, as recently rejported 1221.

C. GLASS TRANSITION TEMPERATURE (7Tg)

T9 was determined by calorimetry using a Differential Scanning Calorimeter (Perkin-

Elmer DSC-4). 'Fhe midpoint of the endothermic shift, characteristic of *.he transition, was

selected as T9.

REMUTS

In thie preparation of 1-10 mole% crosslinkcd PS inicrobcads by batch copolynerization

of S and DVB, the crosslink density and T9 of samples, corresponding to dlifferent conversions,

wvere dleterminced, Figure I ililustrates the variation of conversion, crosslink density and Twith

reaction timec for 5 mnole% crossliniked P'S beads. By adding DVII icrenmeutally during

copolynierization, we synthesized 1, 2, 5 and 1() niole% "un ifornily"cross lit)kcd I'S microbeads.

By analogy to tlie preparation of 5 iiiole% crosslinked PS beads, described in the Experimental

Details and in Taible 1, incrcemental additions of DVI3 (in S) were added in order to readjust the

calculated concentration of 1)V1 to its initial value. Exact additions are sumnmaz izcd inl 'lables 2-

4. Figures 2-5 indicate the relationship betwecn crosslink density and reaction timec for 1, 2, 5 and

10 mole% crosslinked, PS microbeads, respectively, for b'uth batch copolymerization of S and

DVI3 and for "sinicontinuious" processes involving incremental monomer adldition. Figures 6

and 7 are SEM photonuicrographis of 2 anld 5 niole% crosslinked PS -nicerobeads, respectively,

resulting from semicontinuious copolymnerization.

5

DISCUSSION

Reactivity ratios of S and DVII, dctcrmined under various conditions, indicate that DVII

is a more reactive mnonomer thani S [4-10], so that thc mole fraction of DVII in the feed decreases

with copolymcerization. This is directly reflected in variations in crosslink density. In Figure 8, wc

plot crosslink. density versus convcrsion for 5 mole% DVII in I'S beads from batch

copolymerization. The crosslink denisity of the copolymer formed at low conversion is much

highcr than thc initial concentration of DVII in thc monomer feed. As thc conversion inctcases,

the crosslink density of thc copolymer rapidly decreases. In this case, the integral crosslink

density gapproachecs 5 mole% at high conversioni.

As a result of crossiiuking, polymner chains are immobilized and T9increases [24-271. As

shown in Figure 1 for batch copolymerization, T9 correlates well with crosslink density, as a

function of conversion, although, there was some variability in'r at high conversion. Perhaps this

results from traces of monomer trappcd in largely polymeric beads.

It has been reported [23, 28-33] that the cmulsion poly meri zat ion of S in the absence of

emiulsifier can yield monodispcrse sized microbeads. Apparently, the number of growing particles

in the reaction mixture renmins constant with increasing conversion, with growth l3rocedling in

the absence of new particle nucleation 128, 29, 311. In the course of polymerization, polymer

particles increase monotonically in size 123]. In this work, we demionstrate that the crosslink

density decreases with increasing conversion. If we assume tli-t newly formed copolynier adds to

the surfaces of growing beads [17, 181, the ciossliink density of a PS beaid decreaCs from1 Center- to

surface, and copolymer at the particle surface may be uncrosslinked or lightly crosslinked.

Thlerefore, the PS bead from batch copolymerization is hecterogeneously crosslinked, with a

crosslink density gradient through the bead.

For batch cojpolyneiizatiuns of S containing 1, 2, 5 or 10 mole% of l)VI3, we observe that

the crosslink density of iesultant I'S beads dccieases markedly with rcaktion time (I igum es 2 5).

We anticipate that crosslink density curves should level off at initial concentrat ions of DVB, as

the cumulative mole fraction of DVB in thc copolymer polymerized to high conversion should

approach the mole fraction of DVJ3 in the feed. This is approximately true at 2 and 5 mole%

DVB, but is about 20% lower at 1 and 10 mole% DVB (Figure 5). Moreover, if we plot crosslink

density versus conversion for 5 mole% DVB, the curve does not appear to level off at high

conversion (Figure 8). We suggest that, in a heterogeneously crosslinked system, the crosslink

density determined by swelling may not correspond exactly to the mole fraction ofcrosslinkcr in

the copolymer. This is intrinsic to the swelling calculation ,2J and is increasingly true at higher

crosslink densities. Moreover, in batch copolymerization, final conversions attained 70-80%.

In order to prepare homogeneously crosslinked PS beads from copolymerization of S and

DVB, the initial concentration of DVB in the monomer mixture must be reduced and, then,

continuously supplemented during copolymerization. Addition of DVB during copolymerization,

according to the schemes in Tables 1 to 4, yielded relatively uniformly crosslinked microbeads

(Figures 2-5). Moreover, resultant crosslinked PS beads were spherical and monodisperse in size

(Figures 6, 7).

The crosslink density of unifornly crosslinked PS beads was particularly sensitive to the

initial concentration of DVB in the monomer mixture. For example, if the initial concentration of

DVB is increased from 2.5 to 3 mole%, the crosslink density increased fr'om 5 to 7.5 mole%.

Similarly, for a change in initial concentration of DVB from 1.2 to 1.5 mole%, the corresponding

crosslink density increased from 2 to 3 nole%. We have indicated the initial concentration of

DVB for the preparation of uniformly crosslinked PS beads ('Ta4bles 2-4). Since published values

[4-10] of reactivity ratios for S and DVB were derived from solution or bulk cop)olymerization,

they may not apply to the initial stages of emutlsion polymerization and, so, cannot be used to

directly predict tie initial concentration of DVB.

For the synthesis of uniformly crosslinked PS beads, the incremental addition of DVB was

determined from the conversion curve for batch copolymerizatioln. "'hirefore, the stability of

7

operating conditions and the reproducibility of reactions were very important. Small variations inl

reaction rates lead to marked deviations in crosslink density, as chianges in DVII coiicentratiomin

the monomer mixture wcre reflected in drifts !in crosslink density.

Ini later stages of emulsion copolymierization, thie reaction rate often changes as monoiner

droplets in emulsion arc depleted and tlie mionomer conicentration decreases inl gr-owing swollen

bcads. Therefore, the maximum conversion often varied by as much as Mk. Hlowever, in

"1semicontinuous" copolynmerization at high conversion, it was occasionally observed that thie

conversion levelled off prematurely. This would imply that thie reaction ra,!e increased at finial

stages of copolymerization. Per-haps, final inecments of DVII and S, which aire always enriched

in D13I, are not completely incorporated into growing beads. This may prodluce microbeads

surrounded by at hard shiell of increased crosslink density, Ini order to avoid ain abrupt iirase inl

crossimik density at the end of copolymerization, it is necessary to termiate, incremental additions

of DVII and S before the rate of copolymerization decreases.

CONCLUSIONS

Monodisperse sized crosslinked PS beads p~repared by reaction of S and DVII, in batch

emulsion copolymerization in the absence, of emutlsifier, are not uniformly crosslijiked. Since

DVII is more reactive thian S, the mole fraction of l)VI in the monomer feed decreases wihi

cop~olymerization, leading to reductions to Tand crosshink density with increrasing conversion.

For copolymerization of S and 1 to 10 mole % DI)13, crosslinked PS microheads, isolated at

various stages of conversion, decrease in crosslink density by a factor exceeding two. At final

conlversions, appjroximating 75%, the cumulative mole flaction of crosslinks in the copolymer

alplroaches the mole1 fraction of DVII in time feed for copulymcrizations of 2 and 5 mole % DVI3,

but is about 20% lower at 1 and 10% DVII.

Techniques for semicontinuous cop~olymerization, involving incremental additions of

DVII, were devised to produce uniformly crosslimiked PS microbeads. Helre, the initial

8

concentration of DVB ini the monomer mixture was nmrkedly reduced, for example, to 2.5% to

produce 5 mole % crosslinking. By comparison to kinetic curves for corresponding batch

copolynmerizationi, subsequent additions of DVB were made at 10% conversion intervals, in order

to readjust the calculated concentration of l)VB to its initial value.

For both batch and semicontinuous processes, T 9 correlates well with crosslink density.

Mvorcovcr, crosslinked PS beads, from either process, arc spherical and monodisperse in iiIze.

ACKNOWLEDGEMENT

This work was supported in part by the Office of Naval Research and by DARPA.

I 1

REFERENCES

1. T. Alfrey, Jr., J. J. Bohrcr and H. Mark, Copolymerization, Interscience, New York-London, 1952.

2. P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, Ithaca, New York,1953.

3. P. Rcmpp and E. W. Merrill, Polynter Synthesis, Hucthig & Wepf Verlag Basel,Heidelberg, New York, 1986.

4. R. H. Wiley and E. E. Sale, J. Polym. Sci., 42, 491 C1960).

5. R. 1-. Wiley and 13. Davis, Polpit. Letters, 1, 463 (1963).

6. R. 11. Wiley, W. K. Mathews aid K. F. O'Driscoll, J. Macromol. Sci.-Chem., Al, 503(1967).

7. R. 11. Wiley and Tac-Oan Aim, J. Polyn. Sci., Part A4, 6,1293 (1968).

8. R. H. Wiley, S. Prabhakara Rao, J ung-l Jin and K. S. Kim, J. Macromol. Sci.--Chem., A4,1453 (1970).

9. R. 11. Wiley, Pure Appl. Chem., 43, 57 (1975).

10. C. D. Frick, A. Rudin and R. 11. Wiley, J. Mlacromol. Sci.--Chem., A 16, 127. (1981).

11. R. 1H1. Wiley, J. K. Allen, S. P. Chang, K. E. Musselman and "I K. Venkatachalam, J. Phys.Chem., 68, 1776 (1964).

12. R. 11. Wiley, G. Do Velto and F. E. Martin, J. Macronol. Sci.--Chem., Al, 137 (1966)

13. R. II. Wiley and T1. K. Venkatachalam, J. Polym. Sci., Part A, 3, 1063 (1965).

14. R. 11. Wiley and . T. Badgett, J. Macromol. Sci.--Chem., A2, 103 (1968).

15. R. 11. Wiley and E. Reich, J. Polym. Sci., Part A-i, 6, 3174 (1968).

16. R. 11. Wiley and L. 11. Smithson, Jr., J. Macrolnol. Sci.--Chemn., A2, 589 (1968).

17. J. Ilearn, M. C. Wilkinson, A. R. Goodll anl M. Chainey, J. lPol)ym. Sci: Poiaym. Chem.E1., 23, 1869 (1985).

10

-I

18. W. Lau, D. G. Wcstmoreland and R. W. Novak, Macromolecules, 20, 457 (1987).

19. M. A. Linid, A. Klein, L. 11. Sperling and G. D. Wignall, J. Macromol. Sci.--Plhys., B27,181 (1988).

20. S. Yang, A. Klein and L. H. Sperling, J. Poyin. Sci.: Part B: Polyin. Phys., 27, 1649(1989).

21. G. D. Wignall, Y. R. Ramakrisinan, M. A. Linnd, A. Klein, L. 11. Sperling, M. P. Wai, R.A. Gelman, M. G. Fatica, R. II. Hoei, L. W. Fisher, S. M. Melpolder and J. M. O'Reilly,Mol. Cryst. Liq. Cryst., 180A, 25 (1990).

22. Z. Y. Ding, J. J. Aklonis and R. Salovey, J. Polyn. Sci.: Part B: Phys., in press.

23. D. Zou, V. Dedich, K. Gandhi, M. Park, L. Sun, I). Kriz, Y. 1). Lee, G. Kim, J. J. Akionisand R. Salovey, J. Polyin. Sd.: Part A: Polym. Chem., 28, 1909 (1990).

24. K. UcbcrrCiter and 0. Kanig, J. Chem. Phys., 18, 399 (1950).

25. T. G. Fox and S. Loshack, J. Polym. Sci., 15, 371, 391 (1955).

26. M. F. )rum, C. W. 11. Dodge and L. E. Neilsen, Ind. Eng. Chem., 48, 76 (1956).

27. L. E. Neilsen, J. Macromol. Sci.--Revs. Macromol. Chem., 63, 69 (1969).

28. A. R. Goodall and M. C. Wilkinson, .,. Polyin. Sd.: Polyin. Chem. Ed., 15, 2193 (1977).

29. A. R. Goodall, M. C. Wilkinson and J. Ilearn, in Polymer Colloids 11, R. M. Fitch, Ed.,Plenum Press, New York, 1980.

30. J. Hearn, M. C. Wilkinson , A. R. Goodall and M. Clhiney, J. Polti. Sci.: Polyin. C/hem.Ed., 23,1869 (1985).

31. Wen-Yen Chiu and Chi-Cho Shih, J. Appl. Polyn. Sci., 31, 2117 (1986).

32. M. Chainey, J. Ilearn and M. C. Wilkinson, J. Polyn. Sei.: Part A: Polyn. Chem., 25, 505(1987).

33, Zhiqiang Song and G. NV. Poelein, J. Polyn. Sci.: Part A: Polyin. Chem., 28, 2359(1990).

11

a I

Table 1. Addition of DVB Mixtures for 5 nole% DVB-IS Beads (I)VB:S = 3:7 by weight)

Rcaction Time (mili.) 60 96 123 147 165 183 204 231

Amount (g) 2.73 2.51 2.31 2.13 1.97 1.80 1.67 1.55

12

Table II. Addition of DVII mixtures for I mole % DVB-PS Bleals (I)VII: S = 1:9)

Initial Concentration of DVB in Monomer Mixture: 0.6 inole %

Reaction Timc (min.) 51 81 105 123 141 156 168 186 219 260

Amount(g) 2.43 2.23 2.07 1.91 1.77 1.59 1.50 1.37 1.26 1.18

13

Table Ill. Addition of DVI mixtures for 2 i1ole % DV-I'S Beads (DVII: S = 1:9)

Initial Concentration of I)VB in Monomer Mixture:1.2 mole %

Reaction Time (min.) 57 84 108 128 147 165 181 196 218 248

Amount (g) 3.00 2.73 2.55 2,33 2.16 2.02 1.86 1.69 1.58 1.46

14

Table IV. Addition of DVB mixtures for 10 mole % DVII-PS Beads (V13: S = 1:1)

Iniial Concentration of i)VII in Monomer Mixture:3.5 imole %

Reaction Timc (min.) 57 94 129 154 175 193 210 225

Aiuount (g) 4.07 3.77 3.51 3.26 3.04 2.83 2.63 2.46

15

LIST OF FIGURES

1. Variation of Conversion, Crosslink Density (XLD) and Glass Transition Temperature (T )with reaction time for 5 tool% DV13/PS beads from batch copolymcrizafioi.

ConversionX XLDA 7g

2. Variation of XLD with reaction time for 1 tiol% DVB/PS beads.

-A ------- A- batch copolymerizationsuccessively adding DVB

3. Variation of XLD with reaction Iime for 2 tool% DVB/PS beads.

A- ...... A---- batch copolymerization. successively adding DVB

4. Variation of XLD with reaction time for 5 mol% DVB/PS beads.

----A ....... A--- batch copolymcrization0 succCssively adding DVI3

5. Variation of XLD with reaction time for 10 mol% DVB/PS beads.

....A ...... A---- batch copolymerization

successively adding DVB

6. Monodisperse PS beads, crosslinked with 2 nol% DVB, prepared by successively addingDVB, scanning electron micrograph, magnification 10,000 x, 505 nm.

7. Monodisperse PS beads, crosslinkcd with 5 tool% DVB prepared by successively addingDVB, scanning electron micrograph, magnification 10,000 x, 438 in.

8. Variation of XLD with conversion for 5 mol% DVB/PS beads froni batchcopolymerization.

16

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(JUN 1 1i99

TECHNICAL REPORT DISTRIBUTION LIST - GENERAL

Office or Naval Research (2)'" pO . Richard W. Drisko (1)Chemistry Division, Code 1113 Naval Civil Engineering800 North Quincy Street LaboratoryArlington, Virginia 22217-5000 Qpde L52

POtt Hueneme, CA 93043

Dr. James S. Murday (1) Dr. Harold H. Singerman (1)Chemistry Division, Code 6100 David Taylor Research CenterNaval Research Laboratory Code 283Washington, D.C. 20375-5000 Annapolis, MD 21402-5067

Dr. Robert Green, Director (1) Chief of Naval Research (1)Chemistry Division, Code 385 Special Assistant for MarineNaval Weapons Center Corps MattersChina Lake, CA 93555-6001 Code 00MC

800 North Quincy StreetArlington, VA 22217-5000 1$9qdDr. Eugene 280C. Fischer (1) 0o

Code 2840David Taylor Research Center Defense Technical InformationAnnapolis, MD 21402-5067 Center (2)

Building 5, Cameron StationAlexandria, VA 22314

Dr. Elek Lindner (1)

Naval Ocean Systems CenterCode 52San Diego, CA 92152-5000

Commanding Officer (1)Naval Weapons Support CenterDr. Bernard E. DoudaCrane, Indiana 47522-5050

* Number of copies to forward

11i

EtCo 1 r±A

Dr. John J. AklonisDept. of ChemistryUniv. of So. CaliforniaLos Angeles, CA 90009

Dr. Ali S. Argon Dr. William DoaneMechanical Engineering Dept. Liquid Crystal In1situteMassachusetts Inst. of Techin. Kent State UniversityCamrbridge, MA 02139 Kenit, OH 44242

Dr. James Economy Dr. Alan D. MacDlarmilMat. Sdl. & Eng. DeptDpatetoCeisrUnivrsit ofIllioisUniversity of PennsylvaniaUrbana, IL 61020-6219 Philadelphia, PA 19104

Dr. Charles L, McCormick Dr. Edward T. SamulskiDepariment of Polymer Science Dept. of ChemistryUniversity of Southern Mississippi Univ. of North CarolinaH~attiesburg, MS 39046 Chapel Hill, NC 27599.3290

Dr. William P. Weber Dr. Martin PomerantzDept. of Chemistry Department of ChemistryUniv. of Southern Calif. Univ. of Texas at ArlingtonLos Angeles, CA 90089.166al Box 19065'Arlington, TX 70 1 9.00cs

JUN I i

Dr. Ronald Salovey Dr. Jerry 1. ScheinbernDept. of Chemn. Engineering Dept. of Mech,. & Mater. Sdi.Univ. of Southern California Rutgers UniversityLos Angeles, CA 90089 Piscataway, NJ 003854