surface functionalization of polymer latex particles. ii. catalytic oxidation of poly(methylstyrene)...

Surface Functionalization of Polymer Latex Particles. II.Catalytic Oxidation of Poly(methylstyrene) Latexes inthe Presence of Cetyltrimethylammonium Bromide

PEI LI,1 JIANG HONG LIU,1 TING KWOK WONG,1 HAK PING YIU,1 JUN GAU2

1 Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom,Kowloon, Hong Kong

2 Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong

Received 13 January 1997; accepted 23 May 1997

ABSTRACT: Surface-functionalized cationic poly(methylstyrene) (PMS) latex particlescontaining aldehyde and carboxylic acid groups were successfully achieved via an emul-sion polymerization of 3(4)-methylstyrene in the presence of cetyltrimethylammoniumbromide, followed by an in-situ oxidation catalyzed by copper chloride and tert-butylhydroperoxide (t-BuOOH). Factors such as the type of metal catalyst, oxidant, andtheir concentration strongly affected the rate of oxidation. Step addition of t-BuOOHresulted in both a higher degree of oxidation and a more uniform distribution of particlesize of the functionalized PMS as compared to the batch addition method. The effectof organic solvent was found to be insignificant, and the oxidation could still proceedin its absence. The particle sizes increased significantly during the oxidation but couldbe controlled by using crosslinked PMS latexes. Finally, the versatility of this oxidationprocess was demonstrated by oxidation of the polymer with a solid loading as high as28%. q 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3585–3593, 1997Keywords: poly(methylstyrene); catalytic oxidation; functional latex particles

INTRODUCTION emulsifier-free emulsion copolymerization of sty-rene/acrolein mixture,9 and emulsifier-free emul-sion copolymerization of styrene with p -formyl-Functional polymer microspheres with well-de-

fined colloidal and surface characteristics have re- styrene.10 Polymer latexes having carboxylic acidgroups on the surface are commonly prepared byceived much interest because they can provide

useful models for fundamental studies and can the emulsion copolymerization of acrylic acid ormethacrylic acid with a matrix monomer.6 Onefind a wide range of applications as binders or

solid support.1,2 Among the different functional major drawback in these copolymerization pro-cesses is the difficulty in simultaneously control-groups on the particle surface, aldehyde and car-

boxylic acid groups are especially useful for the ling the number of functional groups on the parti-cle surface and the particle size. In order to solvecovalent bonding of amino group-containing bio-

molecules under mild conditions.3–6 Polymer par- this problem, Okubo and his co-workers reportedthe use of the seeded aldol condensation polymer-ticles bearing aldehyde groups have been pro-

duced by homopolymerization or copolymeriza- ization technique with glutaraldehyde in the pres-ence of polymer particles of which size and monod-tion of acrolein in the presence of a surfactant,7,8

ispersity can be preliminarily controlled.11 In ad-dition, chemical modification of the preformed

Correspondence to: P. Lilatexes is an alternative approach for introducing

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 35, 3585–3593 (1997)q 1997 John Wiley & Sons, Inc. CCC 0887-624X/97/163585-09 desired functional groups on the surface with the

3585

97-017P/ 8g51$$017p 09-17-97 19:05:31 polca W: Poly Chem

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control of particle size. For example, benzyl halide NMR spectra were recorded on a JEOL EM400spectrometer. Differential scanning calorimetrygroups on the surface of poly(styrene-co-chloro-

methylstyrene) latexes were converted to benzal- (DSC) was measured under nitrogen on a MettlerDSC 30 with a Mettler TC10A processor at a heat-dehyde groups by oxidation with 2-nitropropane

in aqueous sodium methoxide.12 ing rate of 107C/min. Particle sizes and size distri-butions were measured on a Coulter LS 230 parti-In the previous study, we have reported that

anionic poly(methylstyrene) latexes containing cle size analyzer. Finally, elemental analyseswere performed at MEDAC Ltd., Department ofsurface aldehyde and carboxylic acid groups can

be prepared by the emulsion polymerization of Chemistry, Brunel University, Middlesex, U.K.methylstyrene in the presence of sodium dodecylsulfonate, followed by an in-situ oxidation cata-

Preparation of Cationic Poly(methylstyrene)lyzed by copper(II) chloride and tert-butyl hydro-Latex Particlesperoxide in the presence of tert-butyl alcohol un-

der air.13 The major disadvantage of this system Cetyltrimethylammonium bromide (CTAB) (0.1 g)was that the anionic surfactant tended to bind to dissolved in 50 mL of deionized water was placedthe metal cations of the catalyst, resulting in its into a three-necked jacketed flask equipped withdeactivation. This problem could be overcome by a mechanical stirrer and a nitrogen inlet tube. Athe addition of small amounts of tert-butyl alcohol solution of AIBN (0.10 g) dissolved in purified 3(4)-which solvated the metal cations, resulting in the methylstyrene (10.0 g) was then added dropwise toreduction of this kind of complexation. Therefore, the reaction flask. The mixture was first stirred atit was postulated that cationic latexes might not 350 rpm at room temperature under nitrogen for 24encounter this problem due to the electrostatic h to obtain a stable emulsion, and then the reactionrepulsion between the cationic particle surface temperature was raised to 607C for another 48 h.and cationic ions. Hence, as part of our continuing The poly(methylstyrene) was isolated by precipita-studies on the surface functionalization of poly- tion of the emulsion into methanol. The white pre-mer latexes, we report here our studies on the cipitate was dissolved in THF, followed by reprecipi-metal-catalyzed surface oxidation of cationic poly- tation in a large quantity of hot water, then filtered(methylstyrene) in the presence of cetyltrimethyl- again, and washed with methanol. The product wasammonium bromide. vacuum dried at 507C for 24 h, giving 85% isolatedpolymer. The structure of the polymer was con-

EXPERIMENTAL firmed by IR and 1H-NMR.

MaterialsPreparation of Crosslinked Poly(methylstyrene)3(4)-Methylstyrene from Aldrich Chemical Co.Latex Particleswas freed from phenolic inhibitor by washing with

10% sodium hydroxide solution and then deion- Crosslinked poly[3(4)-methylstyrene] latex par-ized water until the pH of the monomer dropped ticles (4% solid) were prepared using cetyltri-to 7 prior to use. Azobisisobutyronitrile (AIBN) methylammonium bromide (CTAB) and divinyl-(China National Chemicals) was purified by re- benzene as cationic surfactant and crosslinker, re-crystallization in ethanol. All metal salts includ- spectively. AIBN (0.025 g) was dissolved in aing cobalt(II) acetate tetrahydrate (Aldrich), co- mixture of 3(4)-methylstyrene (2.0 g) and divi-balt(II) chloride hexahydrate (Ajax), iron(II) nylbenzene (0.04 g), which contained 55% divi-chloride hexahydrate (China National Chemi- nylbenzene and 45% ethylstyrene (crosslinkingcals) , copper(II) chloride hydrate (BDH), and density Pc Å 1/100). The mixture was then addedmanganese(II) chloride (May & Baker) were dropwise to a solution containing CTAB (0.16 g)used as received. Cetyltrimethylammonium bro- and deionized water (45 mL) and was continu-mide (BDH), tert-butyl hydroperoxide (80%), and ously stirred mechanically at 350 rpm under ni-tert-butyl alcohol from Riedel de Haen were also trogen at 307C for 24 h to obtain a stable emulsion.used without further purification. The reaction temperature was then raised to 707C

for another 48 h. The crosslinked poly(methyl-Instruments styrene) was isolated by precipitation of the emul-

sion into methanol. The white precipitate wasInfrared spectra were recorded on a Nicolet 750FT-IR spectrophotometer using KBr disks. 1H- washed by excess amounts of hot water, followed


CATALYTIC OXIDATION OF POLY(METHYLSTYRENE) 3587

by methanol. The polymer was vacuum dried at as the percentage of carbon, hydrogen, and nitro-gen. The nitrogen content was attributed from the507C for 24 h.presence of a trace amount of cetyltrimethylam-monium bromide. By subtraction of the percent

Catalytic Oxidation of Poly(methylstyrene) C, H, N, and Br atoms contributed by CTAB, theLatex Particles empirical formula could be deduced. For example,

calculation of percent oxidation of poly(methyl-Cetyltrimethylammonium bromide (0.1 g) dis-solved in 30 mL of deionized water was mixed styrene) obtained by step addition method is

shown below.with 10 mL of the prepared noncrosslinked poly-(methylstyrene) emulsion (equivalent to 1.7 g ofPMS). After the mixture was stirred at 607C for Calculation of Empirical Formula1 h under air, copper chloride hydrate (0.14 g)

Results of the percent composition obtained fromdissolved in 7 mL of deionized water was chargedelemental analysis are as follow:to the emulsion dropwise at the rate of 4 mL/min,

followed by the batch addition of 1 mL of tert-C % Å 81.24%; H % Å 7.71%; N % Å 0.42%butyl hydroperoxide (80%) which was diluted in

2 mL of water. The degree of oxidation was moni-After subtraction of the percent carbon and hydrogentored by withdrawing small amounts of sample atcontributed by the CTAB, and determination of thedifferent intervals for analysis by FT-IR spec-percent oxygen in the sample by difference, the em-trometry. The oxidized PMS was recovered quan-pirical formula was determined to be C12.2H12.6O1.0.titatively by precipitation of the emulsion into ac-

etone or a mixture of acetone and methyl ethylCalculation of Percent Oxidationketone. It was subsequently washed with concen-

trated hydrochloric acid to remove the metal salts Assume the oxidized poly(methylstyrene) prod-incorporated in the polymer and then further uct was mainly as follows:washed with deionized water until a pH of 7. Theoxidized PMS in the form of a light-yellow powderwas reprecipitated from THF into a large quantityof hot water to remove surfactant residue, fol-lowed by drying in vacuo at 507C for 24 h.

Oxidation of crosslinked PMS particles wascarried out under the same conditions at 607C for24 h. To remove surfactant residue from the poly- No. of C Å 9x / 9ymer, the precipitate was highly swelled in THF

No. of H Å 8x / 10yand then reprecipitated in hot water. This processwas repeated three times, and the light-yellow No. of O Å 2xpolymer was vacuum dried at 507C for 24 h.

To study the effect of oxidation of PMS latexes Therefore, (9x / 9y ) : (8x / 10y ) : 2x Å 12.2 :by step addition method, the reaction was con- 12 : 6 : 1.0. Solution of this equation yields x %ducted according to the general procedure except Å 37%. Hence, it is claimed that 37% of thethat the concentration of PMS was doubled. In poly(methylstyrene) was oxidized.addition, t-BuOOH (1 mL, 80%) was first dilutedin 6 mL of H2O, and then 1 mL of this diluted t-BuOOH solution was added at hourly intervals RESULTS AND DISCUSSIONfor the initial 7 h.

Preparation of Cationic Poly(methylstyrene)Latex ParticlesCalculation of Percent Oxidation

from Elemental Analysis The procedure used for the synthesis of poly-[3(4)-methylstyrene] (PMS) latexes in the pres-Samples of the oxidized poly(methylstyrene) for

elemental analysis were carefully purified via 3- ence of cetyltrimethylammonium bromide wassimilar to that in the literature with slight varia-fold reprecipitation from THF by using excess

amounts of hot water in order to remove surfac- tions.14 In our system, a 17% PMS emulsion wasprepared in the absence of a crosslinker alongtant residue and metal salt. Results were reported


3588 LI ET AL.

Table I. Effect of Metal Catalysts on the Oxidationof Poly(methylstyrene) Latexesa

Metal Catalyst Mole Ratio Estimated %(0.013M) PMS : Catalyst Oxidationb

Scheme 1. Emulsion polymerization of methylsty-rene, followed by the catalytic oxidation. Co(OAc)2r4H2O 20 : 1 12

CoCl2r6H2O 20 : 1 15CuCl2rxH2O 20 : 1 18

with a much lower surfactant concentration (Ws / MnCl2 20 : 1 0.2Wm Å 0.01, where Ws Å weight of CTAB, Wm FeCl2r6H2O 20 : 1 2.5Åweight of methylstyrene). The yield obtained was

a Reaction conditions: A total of 30 mL of emulsion con-85%, and the size of the particles had a mean diame-taining PMS (0.85 g), metal catalyst (0.013M), t-BuOOH (0.5ter of 112 nm with a coefficient of variation of 50.4%. mL, 80%, 0.13M) and t-BuOH (5 mL) was reacted at 607C for4 h under air.In the case of the synthesis of crosslinked poly-

b Estimated percent oxidation was calculated based on the(methylstyrene) latex particles, higher surfactantelemental analysis as shown in the Experimental section.concentration (Ws /Wm Å 0.08) was used in order to

obtain a stable emulsion. The size of the particleshad a mean diameter of 108 nm with a coefficient

chloride catalysts gave more stable oxidized PMSof variation of 41.3%. The stable cationic PMS emul-emulsions which remained stable for a long periodsions obtained were used directly for the subsequentof time, while the use of cobalt acetate resulted inoxidation reactions.phase separation after a few days. This instabilitymay be due to the reduction of the electrostatic

Catalytic Oxidation of Poly(methylstyrene) repulsion as a result of the acetate anions associ-Latex Particles ating with the surfactant cations, reducing the

charge density on the particle surface.In our first paper,13 we reported that the catalyticThe effect of CuCl2 concentration on the rateoxidation of poly(methylstyrene) (PMS) latex

of oxidation of PMS latexes was investigated byparticles in the presence of sodium dodecyl sul-varying the mole ratio of PMS to CuCl2 from 100 :fonate was successfully achieved by using the1 to 10 : 1. Results in Table II showed that CuCl2CuCl2 / t-BuOOH/ t-BuOH oxidative system. Inconcentration had a slight effect on the degree ofthis paper, we focused on the catalytic oxidationoxidation. However, PMS : CuCl2 Å 50 : 1 gaveof cationic PMS latexes in the presence of cetyltri-the highest degree of oxidation among the ratiosmethylammonium bromide (Scheme 1). The reac-studied. It was also noted that when PMS : CuCl2tion proceeded via a free-radical mechanism in- Å 10 : 1, carboxylic acid was the major functionalvolving metal-catalyzed decomposition of t-Bu-group while the aldehyde group was the majorOOH and benzylic oxidation as proposed in theone at lower CuCl2 concentrations as shown inprevious paper.13 The effects of various reactionFigure 1. These results suggested that higherparameters were investigated, and the control ofCuCl2 concentration facilitated the oxidation ofparticle size and number of surface functionalaldehyde to the corresponding carboxylic acid.groups was attempted.

Effect of Metal Catalyst Table II. Effect of Concentration of CuCl2 on theOxidation of Poly(methylstyrene) Latexesa

The type of metal catalyst used was found tostrongly affect both the rate of oxidation and the Conc. of Mole Ratio Estimated %stability of the latexes. Five metal salts, Co- CuCl2 (M) PMS : CuCl2 Oxidation(OAc)2)r4H2O, CoCl2r6H2O, CuCl2rxH2O, FeCl2r6H2O, and MnCl2, were examined. Table I shows 0.004 100 : 1 18

0.008 50 : 1 24that copper chloride gave the highest degree of0.02 20 : 1 20oxidation among all the catalysts studied. The su-0.04 10 : 1 16perior effect of CuCl2 for the surface oxidation of

cationic PMS latexes was similar to its effect on a Reaction conditions: A total of 50 mL of emulsion con-the oxidation of anionic PMS latexes as discussed taining PMS (1.7 g), CuCl2 at various concentrations, and t-BuOOH (1 mL, 0.8%) was reacted at 607C for 4 h under air.in the previous paper.13 Furthermore, use of metal



Figure 1. Effect of CuCl2 concentration on the oxidation of poly(methylstyrene) la-texes; (a) 0.04M (PMS : CuCl2 Å 10 : 1); (b) 0.02M (PMS : CuCl2 Å 20 : 1); (c) 0.008M(PMS : CuCl2 Å 50 : 1); (d) 0.004M (PMS : CuCl2 Å 100 : 1). Reaction conditions:Refer to the general procedure for the catalytic oxidation of PMS latexes.

Effect of the Concentration of electrostatic repulsion between the cationic PMStert-Butyl Hydroperoxide latex particles and the metal cations of the cata-

lyst. Thus, the presence of t-BuOH, which servesThe effect of tert-butyl hydroperoxide (t-BuOOH)to prevent complexation between functionalconcentration on the rate of oxidation was investi-groups on the particle surface with metal ions,gated by varying its concentration from 0.027 tobecomes unnecessary. Therefore, subsequent0.24M. Table III shows that the degree of oxida-studies on the catalytic oxidation of cationic PMStion increased as the amount of t-BuOOH wasparticles were carried out in the absence of anincreased. However, when the concentration wasorganic solvent.exceeded 0.24M, the oxidation reaction became

too vigorous to monitor.

Effect of Organic Solvent Effect of the Addition Method of Oxidant

The effect of t-BuOH, which was critical in theTwo addition methods of the oxidant, t-BuOOH,catalytic oxidation of the anionic PMS system,were examined under the same reaction condi-was investigated by varying the concentration oftions: (i) All the oxidant was charged into thesolvent to water ratio from 1 : 1.25 v/v to 1 : 5. Itreaction vessel at once (batch addition). ( ii ) Thewas found that the rate of oxidation was indepen-oxidant, diluted in water, was charged at hourlydent of the amount of tert-butyl alcohol added. Inintervals (step addition). It was found that thefact, the oxidation proceeded even in the absencedegree of oxidation was remarkably higher for theof an organic solvent. This is likely due to thesecond method determined by FT-IR. Results ofelemental analysis indicated that percent oxida-

Table III. Effects of t-BuOOH Concentration on the tions were 21% and 37% for methods (i) and (ii) ,Oxidation of Poly(methylstyrene) Latexesa respectively. A possible explanation for this effect

is due to a recombination reaction between peroxyConcn. of Mole Ratio Estimated % radicals themselves and with polymer radicals at

t-BuOOH (M) PMS : t-BuOOH Oxidation relatively high concentration, thus reducing theinitiation efficiency. The use of a lower concentra-0.027 9 : 1 õ 1tion of oxidant can significantly increase the prob-0.08 3 : 1 9ability of successful oxidation of the polymer.0.13 2 : 1 12Hence, a continuous supply of low concentrated0.20 1.2 : 1 18

0.24 1 : 1 28 oxidant, throughout the initial period, can effec-tively oxidize the polymer. Furthermore, the addi-

a Reaction conditions: A total of 30 mL emulsion containing tion methods affect the particle size and size dis-cobalt acetate (0.1 g, 0.013M), PMS (0.85 g), and t-BuOH (5mL) was reacted at 607C for 4 h under air. tribution which will be discussed later.


3590 LI ET AL.

percentage of oxidation. This result demonstratesthe versatility of this process for industrial appli-cations.

Characterization of Poly(methylstyrene)Latex Particles

Figure 3 shows the IR spectra of the polymer atdifferent stages of oxidation. Two strong peaksobserved at 1720 and 1700 cm01 corresponded toFigure 2. Reaction kinetics of the oxidation of poly-the aldehyde and carboxylic acid peaks, respec-(methylstyrene) latexes catalyzed by CuCl2/t-BuOOHtively. As the oxidation proceeded, the aldehydeunder air using the batch addition method.peak decreased, indicating that it was being fur-ther oxidized to the corresponding acid. Figure 4shows the 1H-NMR spectrum of PMS oxidized byKinetics of Oxidation of Poly(methylstyrene)the CuCl2/t-BuOOH system after 8 h. The alde-Latexeshyde proton appeared at 9.9 ppm as a singlet,

The reaction was performed using copper chloride while the aromatic hydrogens ortho to the alde-as the catalyst and t-BuOOH, which was added hyde and carboxylic acid groups appeared at 7.8batchwise, as the oxidant at 607C for 48 h. During ppm. On the basis of 1H-NMR integration, thethe oxidation, samples were drawn out at various product contained 5% aldehyde and 25% carbox-timed intervals in order to study its degree of oxi- ylic acid groups.dation by FT-IR and elemental analysis. As shownin Figure 2, the reaction proceeded rapidly, reach-ing 30% oxidation during the initial 10 h, after Thermal Properties of the Oxidizedwhich the rate of reaction significantly decreased. Poly(methylstyrene)The decrease in the rate of reaction could be ex-

The thermal properties of PMS and its oxidizedplained by the decrease in the amounts of bothderivatives were measured by differential scan-the active catalyst and the peroxide which werening calorimetry (DSC). The oxidized derivativesthe key elements involved in the catalytic oxida-were isolated by solvent extraction in a Soxhlettion process. In addition, flocculation of the la-extractor for 24 h. The insoluble PMS gel wastexes was observed after 24 h oxidation. This in-obtained by extraction with toluene followed bystability may be due to two possible reasons: (1)MeOH. Lowly oxidized PMS was isolated from tol-There was an increase in particle size due to theuene, while highly oxidized PMS was obtainedswelling caused by the presence of the carboxylicfrom the MeOH extraction. All the samples wereacid groups on the particle surface. (2) When thetreated under the same thermal conditions. Thepolymer particles were highly oxidized, the sur-glass transition temperature (Tg ) of the PMS in-face functional groups, which were mainly nega-

tively charged carboxylate groups, could formsalts with cationic surfactant molecules that had

Table IV. Effect of Solid Content on the Oxidationleft the particle surface. Consequently, surface of Poly(methylstyrene) Latexesa

charge density was lowered which led to coagula-tion of the polymer particles. % Solid Content of Estimated %

PMS Emulsionb Oxidation

Effect of the Emulsion Solid Content 4 458 40For the practical aspects of this catalytic process,

12 38the effect of solid loading was studied by varying28 32the ratio of polymer content from 4% to 28%. The

concentrations of polymer in solution were altered a Reaction conditions: For a total volume of 25 mL, thereaction was catalytically oxidized by CuCl2 and t-BuOOHwhile the ratio of all other components was kept(molar ratio of PMS: CuCl2 : t-BuOOH Å 20 : 1 : 10), at 607Cconstant. The results summarized in Table IV in-for 24 h under air.dicated that oxidation could proceed up to a high b Percentage solid content was determined based on themass of poly(methylstyrene) in the emulsion.solid content of 28%, with some decrease in the



Figure 3. Comparison of IR spectra of three polymers: (a) pure PMS; (b) oxidizedPMS obtained after 8 h of reaction; (c) highly oxidized PMS obtained after 24 h ofreaction.

creased from 937C to 1187C for the insoluble PMS Particle Size and Size Distributiongel due to crosslinking. The lowly oxidized PMS The mean diameter of the PMS latexes was found(õ5% oxidation) had little change in its Tg value, to increase significantly during oxidation. As il-while the highly oxidized PMS (ú30% oxidation) lustrated in Figure 5a,b, oxidation by the batchwas found to have a lower Tg value (907C) than addition method showed an increase of particleits pure PMS. This lowered Tg value for highly size and broad distribution with a coefficient ofoxidized PMS could be due to the decrease of aver- variation of 138%. The significant increase of theage molecular weight, resulting from backbone particle size could be due to the flocculationcleavage. Such cleavage which has been reported caused by two possible reasons: (1) There is swell-in the literature could be caused by radicals ating of the PMS latexes because of the presencetacking the tertiary hydrogens of the backbone of carboxylic acid groups. (2) The carboxylic acidchain rather than the primary hydrogens of the groups on the particle surface might interact withmethyl group.15–17

the cationic surfactant, thus reducing the totalsurface charge and the stability of the oxidizedPMS latexes. The much broader particle size dis-tribution after oxidation could be attributed to theuneven oxidation. Particles which had little or nooxidation had almost no change in size, while thesize of the highly oxidized PMS particles wasremarkedly increased. For the step additionmethod, a narrower distribution of particle sizeswas obtained in spite of the increase of particlesize (Fig. 5c). Therefore, to achieve a more effi-cient and evenly distributed oxidation, a lowerconcentration of the oxidant should be added atstep intervals during the initial period. In orderto control the size of functionalized PMS particles,Figure 4. 1H-NMR spectrum of poly(methylstyrene)crosslinked PMS latexes could be used for the oxi-oxidized in the CuCl2/t-BuOOH system after 8 h, con-dation. For example, 46% oxidation of the cross-taining 5% aldehyde and 25% carboxylic acid groups

(1H-NMR solvent: acetone-d6) . linked PMS latexes was achieved at 607C for 24


3592 LI ET AL.

h via the batch addition method. Little changein particle size was observed as demonstrated inFigure 6a,b. Thus the particle size and the num-ber of surface functional groups could be con-trolled concurrently when the crosslinked parti-cles were employed.

CONCLUSION

Our studies have shown that functionalization ofcationic poly(methylstyrene) (PMS) latex parti-cles in the presence of cetyltrimethylammoniumbromide can be successfully achieved, using theCuCl2/t-BuOOH/air system at 607C. The use ofCuCl2 for the catalytic oxidation of cationic PMSlatexes was found to have a higher rate of oxida-tion than other metal salts such as CoCl2, MnCl2, Figure 6. Comparison of particle sizes of (a) pureFeCl2, and Co(OAc)2. The presence of an organic crosslinked PMS latexes and (b) 46% oxidized cross-solvent, like t-BuOH, was found to be unimport- linked PMS latexes.ant, as oxidation could still proceed in its absence.A much higher degree of oxidation could beachieved by using the step addition method in- than the batch addition method. Study of the oxi-

dation kinetics showed that a much higher rate ofstead of the batch addition method. Moreover, thestep addition method gave a more uniform distri- oxidation was observed during the initial reaction

period. The industrial versatility of this oxidationbution of particle size of the functionalized PMSprocess was demonstrated by oxidation of thepolymer with a solid content as high as 28%. Dur-ing oxidation, the mean diameter of the polymerparticles increased significantly due to the forma-tion of carboxylic acid groups which might causeflocculation. This increase could be overcome bythe use of crosslinked PMS latex particles. As aresult, the control of particle size and the numberof surface functional groups could be achievedconcurrently.

We are grateful to the Hong Kong Polytechnic Univer-sity for the financial support of this research.

REFERENCES AND NOTES

1. A. Akelah and A. Moet, Functionalization Polymersand Their Application, Chapman and Hall, Lon-don, 1990.

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7. A. Rembaum, M. Chang, G. Richards, and M. Li, 13. P. Li, J. H. Liu, H. P. Yiu, and K. K. Chan, J.Polym. Sci., Part A: Polym. Chem., 35, 1863 (1997).J. Polym. Sci., Polym. Chem., 22, 609 (1984).

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9. C. Yan, X. Zhang, Z. Sum, H. Kitano, and N. Ise, (1991).15. L. P. Ferrari and H. D. H. Stover, Macromolecules,J. Appl. Polym. Sci., 40, 89 (1990).

10. B. Charleux, P. Fanget, and C. Pichot, Makromol. 24, 6340 (1991).16. R. T. Shaver, D. Vlaovic, I. Reviakine, R. Wittaker,Chem., 193, 205 (1992).

11. M. Okubo, Y. Kondo, and M. Takahashi, Colloid L. P. Ferrari, and H. D. H. Stover, J. Polym. Sci.,Part A: Polym. Chem., 33, 957 (1995).Polym. Sci., 271, 109 (1993).

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surface functionalization of polymer latex particles. ii. catalytic oxidation of poly(methylstyrene)...

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