Surface functionalization of polymer latex particles. I. Catalytic oxidation of poly(methylstyrene) latex particles in the presence of an anionic surfactant

Surface Functionalization of Polymer Latex Particles. I.Catalytic Oxidation of Poly(methylstyrene) Latex Particlesin the Presence of an Anionic Surfactant

PEI LI,1 JIANG HONG LIU,1 HAK PING YIU,1 KAN KWANG CHAN2

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 30 March 1996; accepted 27 November 1996

ABSTRACT: A facile synthesis of functionalized poly[3(4)-methylstyrene] (PMS) latexparticles containing aldehyde and carboxylic acid groups was achieved via an emulsionpolymerization of 3(4)-methylstyrene in the presence of sodium dodecyl sulfonate,followed by an in-situ oxidation catalyzed by copper(II) chloride and t-butyl hydroperox-ide (t-BuOOH) in the presence of t-butyl alcohol (t-BuOH). The structure of the anionicsurfactant, metal catalyst, organic solvent, oxidant, and their concentrations stronglyaffected the rate of oxidation and the stability of the emulsion. The average size of thepolymer latex particles was found to increase after oxidation, and the polymer wasslightly crosslinked. A free-radical mechanism is proposed involving metal-catalyzeddecomposition of t-BuOOH and benzylic oxidation. q 1997 John Wiley & Sons, Inc. J PolymSci A: Polym Chem 35: 1863–1872, 1997Keywords: poly(methylstyrene); catalytic oxidation; functionalized latex particles

INTRODUCTION tion of Schiff base at room temperature. Polymerparticles bearing surface aldehyde groups havebeen prepared by various methods. For example,Surface-functionalized latexes have received in-homopolymerization or copolymerization of acro-creasing attention during the past decade for ap-lein in the presence of a surfactant, 3,4 emulsifier-plications in two main areas: ( i ) they can providefree emulsion copolymerization of styrene/acro-useful models for fundamental studies in colloidlein mixtures, 5 emulsifier-free emulsion copoly-science, physics and rheology, ( ii ) they are usedmerization of styrene with p -formylstyrene, 6

in a broad range of applications, e.g., as bindersand seeded aldol condensation polymerization ofin paints, adhesives, paper coatings, textiles,glutaraldehyde in the presence of polystyreneetc., and as solid supports in biochemical and particles.7 Polymer particles having carboxylicbiomedical fields, calibration standards, cataly- acid groups on the surface have also found many

sis, etc.1,2 Among the different functional groups important applications in biomedical and bio-on the surface of polymer particles, aldehyde chemical fields. In addition, they are widely usedgroups are especially useful for the covalent in crosslinkable coatings and adhesives. Thebinding of amino group-containing biomolecules, most commonly used technique to prepare poly-e.g., proteins, drugs, and enzymes, by the forma- mer latices with carboxylic acid groups on the

surface is via the emulsion copolymerization ofacrylic acid or methacrylic acid with a matrixCorrespondence to: P. Limonomer.8 However, this method suffers fromContract grant sponsor: Hong Kong Polytechnic University

q 1997 John Wiley & Sons, Inc. CCC 0887-624X/97/101863-10 two major drawbacks: ( i ) significant differences

1863

/ 8G42$$0237 05-30-97 00:42:08 polca W: Poly Chem

1864 LI ET AL.

in the copolymerization reactivity parameters Attempts to control the particle size and theamounts of surface functional groups will be re-between the functional monomer and the matrix

monomer, results in the formation of water-solu- ported in the subsequent articles.ble functional polymer which causes many diffi-culties in purification, ( ii ) most of the carboxylgroups reside inside the particles rather than on EXPERIMENTALthe surface. Thus, it is quite difficult to controlthe particle size and the amounts of functional Materialsgroups on the surface at the same time. Chemi-

3(4)-Methylstyrene from Aldrich Chemical Co.cal modification of the preformed latex particleswas freed from phenolic inhibitor by washing withhas also been reported. For example, benzyl ha-a 10% sodium hydroxide solution and then deion-lide groups on the surface of poly(styrene-co-ized water until the pH of the monomer droppedchloromethylstyrene) beads were converted toto 7 prior to use. Analytical grade potassium per-benzaldehyde groups by oxidation with 2-nitro-sulfate (K2S2O8) (BDH), cobalt(II) acetate tetra-propane in aqueous sodium methoxide.9hydrate [Co(OAc)2

•4H2O] (Aldrich), cobalt(II)Poly(methylstyrene) has recently received con-chloride hexahydrate [CoCl2

•6H2O] (Aldrich),siderable commercial interest because of a newiron(II) chloride tetrahydrate [FeCl2•4H2O] (Wako),monomer synthesis from toluene and ethylenecopper(II) chloride hydrate [CuCl2

•xH2O] (BDH),that could result in low prices. Methylstyrene alsomanganese chloride (MnCl2) (May & Baker), so-exhibits reactivity analogous to that of styrene.10

dium dodecylbenzene sulfonate (Aldrich), sodiumMost importantly, the methyl group on the phenyldodecyl sulfonate (Aldrich), sodium dodecyl sul-ring provides a reactive site for functionalizationfate (BDH) and octylphenoxypoly(ethoxyetha-without employing chloromethylether, which isnol) (Triton X-100) (Aldrich) were all used asreported to have carcinogenic properties. Al-received. tert-Butyl hydroperoxide (t-BuOOH)though metal-catalyzed selective oxidations of low(70%) was purchased from Riedel de Haen. Othermolecular weight organic compounds in air havechemicals were reagent grade and used withoutbeen extensively studied, selective oxidation offurther purification.polymers have received little attention.11 Re-

cently, a selective oxidation of poly(4-methylsty-rene) with cobalt acetate/sodium bromide in the Instrumentspresence of a mixture of dimethoxyethane andacetic acid was reported12–14 to afford a polymer Infrared spectra were recorded on a Perkin-Elmer

1730 FTIR spectrophotometer using KBr disks.bearing both aldehyde and carboxylic acid groups.This solvent-based selective oxidation process can 1H-NMR spectra were recorded on a JEOL EM400

spectrometer. Gel permeation chromatogramsprepare a series of new functionalized copolymershaving molecular weights from 2000 to 16,500 (GPC) were obtained on a Water’s 410 GPC sys-

tem with differential refractometer. Tetrahydro-and containing up to 20% aldehyde and 90% car-boxylic acid groups. furan was used as the eluent at a rate of 1 mL/min

at 307C. The GPC was calibrated with polystyreneWe were interested in direct surface function-alization of poly(methylstyrene) latex particles standard samples, and the apparent molecular

weights were calculated with the Water’s baselinevia metal-catalyzed oxidation in an aqueous emul-sion. To the best of our knowledge, this novel ap- 810 software. Differential scanning calorimetry

(DSC) was measured under nitrogen on a Mettlerproach has not been reported. The major chal-lenge of the oxidation of the poly(methylstyrene) DSC 30 with a Mettler TC10A processor at a heat-

ing rate of 107C/min. Elemental analysis was per-latex particles was to find a catalytic system thatwould selectively oxidize the methyl groups on the formed at MEDAC Ltd., Brunel University, UK.

The static and dynamic light scattering mea-particle surface to the corresponding aldehydeand acid functionalities, while still maintaining surements were performed with a laser light-

scattering spectrometer (ALVDLS/SLS-5000,the polymer particles in a colloidal state withoutcoagulation. In this article, we mainly concen- Langen, Germany) using an argon ion laser as the

light source (Coherent INNOVA90), operating attrated on the development of a catalytic systemfor this surface functionalization process, as well a wavelength of 488 nm and 400 mW. The latex

dispersions were optimized for the light-scatter-as investigated various factors which affected therate of oxidation and the stability of the emulsion. ing experiments by diluting the crude concen-


POLYMER LATEX PARTICLES. I 1865

trated reaction product with an excess of deion-ized water until the count rate of the resultingmixture was within the optimal range of the spec-trometer. These dilute solutions were purified byfiltering through Millipore HA 0.5 um filters.Scanning electron microscopy (SEM) photomicro-graphs were obtained on a JEOL 6300F instru-ment. Dried specimens were placed on a roundcover glass, which was mounted with double-faceadhesive tape on the stud and then coated under

CH®CH¤

C⁄¤H¤fiSO‹ Na

CuCl¤ /t -BuOOH t -BuOH, 60ƒC

2 1

n

x y z

K¤S¤O°, 80ƒCCH‹

©CH©CH¤©©CH©CH¤©©CH©CH¤©

CH‹ CHO COOH

©CH®CH¤©

CH‹

vacuum with a thin layer of gold to a depth ofabout 5 A. Scheme 1. Emulsion polymerization of methystyrene

followed by catalytic oxidation.

Synthesis of Poly(methylstyrene) Latex Particles

Sodium dodecyl sulfonate (0.18 g) mixed in 50 vigorous stirring, which was followed by the addi-tion of 0.5 mL of t-BuOOH (70%). The emulsionmL of distilled water was added to a 100 mL

two-necked flask equipped with a stirrer and a was stirred and heated at 607C for 22 h in air,and then was diluted to half its original concen-nitrogen inlet tube. The solution was stirred at

607C under nitrogen until all the sodium dodecyl tration and precipitated by the slow addition of asaturated KAl(SO4)2 solution. The oxidized poly-sulfonate dissolved. Purified 3(4)-methylstyrene

(15 mL) was added to the surfactant solution mer in the form of a light yellow solid was recov-ered quantitatively by filtration. It was reprecipi-dropwise, and the emulsion was stirred vigor-

ously for 1.5 h until a stable emulsion was ob- tated from THF solution in a large quantity of hotwater to remove surfactant residue, followed bytained. Potassium persulfate (0.1 g) , dissolved

in 1 mL of water, was then added slowly to the drying in vacuo at 507C.emulsion with stirring. The reaction tempera-ture was maintained at 807C and the emulsionwas allowed to react for 24 h under nitrogen. RESULTS AND DISCUSSIONStable white latices of poly(methylstyrene)(PMS) were obtained at the end of the reaction. The synthesis of the functionalized poly(methyl-

styrene) (PMS) latex particles involved two steps:To isolate the polymer, 10 mL of the emulsionwas diluted with 10 mL of water in a 100 mL emulsion polymerization of 3(4)-methylstyrene

and metal-catalyzed oxidation of the particles inbeaker and precipitated by slowly adding a satu-rated KAl(SO4)2 electrolyte solution with gentle the presence of t-BuOOH (Scheme 1). The emul-

sion polymerization of 3(4)-methylstyrene wasstirring. The white precipitate was filtered anddissolved in THF, followed by reprecipitation in carried out using sodium dodecyl sulfonate as the

surfactant and potassium persulfate (K2S2O8) asa large quantity of hot water, then filtered againand washed with methanol. The product was an initiator. Stable PMS latices were obtained,

which were used directly in the subsequent reac-dried to constant weight in vacuo at 507C giving a98% yield with MV n Å 113,500, and polydispersity tions. The rate of the oxidation and the stability

of the latices were found to be strongly affectedindex Å 2.99. The structure of the polymer wasdetermined by IR and 1H-NMR. by the type and concentration of the surfactant,

the organic solvent, the oxidant and the metalcatalyst used.

Catalytic Oxidation of Poly(methylstyrene) (PMS)Latex Particles

Effect of SurfactantsSodium dodecyl sulfonate (0.3 g) was added to 15mL of distilled water and stirred under air at Three factors had to be taken into account when

selecting the surfactant: (1) the size of the PMS607C. After the PMS emulsion (5 mL, equivalentto 0.9 g polymer) and t-butyl alcohol (5 mL) were latex particles formed, (2) the stability of the

emulsion, and (3) the tendency of the surfactantadded to the reaction vessel, a solution of Co-(OAc)2

•4H2O (0.1 g) dissolved in 4.5 mL of distilled to complex with the metal catalyst. Three differ-ent anionic surfactants were examined includingwater was added dropwise to the emulsion with


1866 LI ET AL.

sodium dodecylbenzene sulfonate, sodium dode-cyl sulfonate, and sodium dodecyl sulfate. They

ROOH 1 M ROı 1 M 1 OHn n 11 2

ROOH 1 M ROOı 1 M 1 Hn n 11 1

were all found to be excellent surfactants for theScheme 2. Metal ion catalyzed decompositions of al-emulsion polymerization of 3(4)-methylstyrenekyl hydroperoxide.giving fine particles. However, the use of sodium

dodecylbenzene sulfonate gave an unstableemulsion during the oxidation, which might be

emulsions or unsuccessful oxidation. 1,2-Dimeth-caused by complexing with the metal catalyst.oxyethane had similar effects as t-BuOH, but itSodium dodecyl sulfate underwent hydrolysis towas oxidized under the reaction conditions used,give the corresponding alcohol. In comparison,thus reducing the efficiency of the catalyst andthe stable emulsion formed with sodium dodecylforming more by-products. The profound solventsulfonate was not greatly affected by the oxida-effect of the t-BuOH for this catalytic reactiontion conditions. Thus, sodium dodecyl sulfonatecould be due to its ability to solvate the cobalt ionswas considered to be the most suitable surfactantthrough weak coordination, thus preventing thefor this reaction system and was used for subse-interaction between cobalt ion and sodium dode-quent studies. A nonionic surfactant, Triton X-cyl sulfonate, while still maintaining the reactiv-100, was also examined, and found that it was aity of the cobalt ion. When a nonpolar solvent suchpoor surfactant for the emulsion polymerizationas heptane or benzene was used, latex particlesgiving relatively large particles. Furthermore,swelled in the presence of these solvents, givingthe emulsion was very unstable during the oxida-unstable emulsions. In contrast, use of strong co-tion. The use of a cationic surfactant was alsoordinating solvents such as CH3CN or N,N-di-investigated, and the results will be reported inmethylformamide significantly decreased thea subsequent article.electrode potential of the cobalt ion, thus render-ing it ineffective in the decomposition of the t-

Effect of Organic Solvents BuOOH. During this study, it was also found thatthe rate of oxidation and the stability of the emul-The organic solvent played an important role insion were affected by the quantity of t-BuOHthe catalytic oxidation system. When the oxida-added. When the concentration of t-BuOH wastion was carried out with air and Co(OAc)2/t-higher than 25% by volume, the latices becameBuOOH in the absence of organic solvents at 607C,unstable. However little oxidation (õ1%) was ob-little reaction was detected. Loss of the catalyticserved when the concentration was less than 10%activity of the cobalt ion might be a result of itsby volume.coordination to the sulfonate ion on the particle

surface. The addition of small amounts of t-BuOHto the catalytic system resulted in the successful Effect of Oxidantsoxidation of the PMS latex particles. The additionof nonpolar solvents such as heptane and benzene The oxidant also played a key role in the cobalt-

catalyzed oxidation reaction. No oxidation was ob-or strong polar solvents like acetonitrile and N,N-dimethylformamide, however, all gave unstable served when oxygen was bubbled through the la-

Table I. Effect of Metal Catalysts on the Oxidation of Poly(methylstyrene) Latex Particlesa

Elemental Analysis

Metal Catalyst C (%) H (%) O (%) Estimated Percent Oxidationb

Co(OAc)2r4H2O 85.97 7.84 6.19 24.2CoCl2r6H2O 88.36 8.24 3.40 13.0MnCl2 88.87 8.33 2.80 10.6CuCl2rxH2O 84.13 7.53 8.34 33.3

a Reaction conditions: refer to the general procedure for the oxidation of PMS particles. Equal mole of metal catalyst was used.b Estimated percent oxidation was calculated based on the structure of poly(vinylbenzoic acid). The actual percentage of the

oxidation might be higher than these values because of the aldehyde groups.



Figure 1. Oxidation rate of poly(methystyrene) latex particles catalyzed by CuCl2

in the presence of t-BuOOH and t-BuOH at 607C under air. The percentage of oxidationwas determined by elemental analysis and calculated based on the structure of poly(vi-nylbenzoic acid).

tex emulsion containing only the cobalt catalyst which dissolved in both water and t-BuOH, wasfound to be an excellent oxidant for this system.and t-BuOH. When hydrogen peroxide was em-

ployed as the oxidant, the reaction proceeded vio- The oxidation reaction could be controlled readilyby varying the amounts of t-BuOOH used. Thelently and was difficult to control. t-BuOOH,

Figure 2. Comparison of IR spectra of two polymers: (a) pure PMS, (b) oxidized PMS.


1868 LI ET AL.

Figure 3. IR spectra of the oxidized poly(methylstyrene) at various reaction timesunder standard conditions.

degree of oxidation decreased as the concentration Effect of Metal Catalystsof t-BuOOH decreased and became negligible

The concentration of the cobalt catalyst signifi-when the concentration was lower than 0.4% bycantly affected the rate of the oxidation and thevolume. However, when t-BuOOH concentrationstability of the emulsion. Decreasing the concen-exceeded 6% by volume, the latex emulsion be-tration of Co(OAc)2 resulted in a reduction in thecame unstable. Finally, little oxidation was ob-oxidation rate. No oxidation was detected whenserved when di-t-butyl peroxide was used as the

oxidant. the concentration of Co(OAc)2 was lower than



Figure 4. 1H-NMR spectrum of the oxidized poly(methylstyrene) containing 2% alde-hyde and 4% carboxylic acid (NMR solvent: acetone-d6) .

0.003M (PMS : Co Å 100 : 1). However, when because it has two valence states of comparablestability. However, the decompositions werethe concentration of Co(OAc)2 exceeded 0.016M

(PMS : Co Å 20 : 1), the emulsion became un- slowed down by the presence of coordinating li-gands such as carboxylic acid groups which werestable.

The use of other metal catalysts such as co- generated during the reaction.16 In comparison,the transformation between copper(II) and cop-balt(II) chloride, manganese(II) chloride, cop-

per(II) chloride, and iron(II) chloride was also per(I) can not only occur by the reaction shown inScheme 2, but also by other mechanistic pathwaysinvestigated (Table I) . The degree of oxidation

obtained was estimated based on elemental anal- that are insensitive to redox potential. These al-ternative pathways leading to the regeneration ofysis. Copper(II) chloride was found to have the

highest reactivity among all the catalysts, while copper(I) , include electron transfer oxidation ofalkyl radicals and ligand transfer.17 Thus the cop-the addition of iron(II) chloride resulted in an

unstable emulsion. The metal ion-induced decom- per(II) salt exhibited higher catalytic activity inthis oxidation system than the cobalt(II) salt.position of alkyl hydroperoxides has been exten-

sively employed as a method for introducing the A preliminary study of the kinetics of the oxida-tion of PMS latex particles catalyzed by cop-alkylperoxy group into a variety of molecules.15

The catalytic decomposition of alkyl hydroperox- per(II) chloride was carried out. The oxidationwas monitored by withdrawing samples at 2 hides is strongly dependent upon the redox poten-

tial of both oxidation and reduction reactions intervals. The degree of oxidation was determinedby elemental analysis (Fig 1). The oxidized poly-(Scheme 2). CoII /CoIII redox system is known to

be one of the most effective autoxidation catalysts mer changed from white to light yellow, and fi-


1870 LI ET AL.

nally to brown during the oxidation indicating theincrease in the degree of oxidation.

Characterization of Latex Particles

Figure 2 shows the IR spectra of the pure PMSand the oxidized PMS, while Figure 3 shows theIR spectra of the oxidized polymer at varioustimes. Two strong carbonyl peaks appeared at1720 and 1700 cm01 indicating the formation ofaldehyde and carboxylic acid groups concurrently.The aldehyde groups were further oxidized to car-boxylic acid groups as the oxidation proceeded.Figure 4 shows the 1H-NMR spectrum of PMSoxidized in Co(OAc)2/t-BuOOH/t-BuOH system

Figure 5. Dynamic light scattering measurement ofafter 6 h. The single aldehyde proton appeared at polymer latex particles: (s ) pure poly(methylstyrene)9.9 ppm, while the aromatic hydrogens ortho to latex particles, hydrodynamic radii (Rh ) Å 37.4 nm,the aldehyde and carboxylic acid group appeared polydispersity Å 1.28; (n ) oxidized poly(methylstyr-at 7.7 ppm. Based on the 1H-NMR integration, the ene) latex particles prepared by Co(OAc)2/t-BuOOH/product contained 2% aldehyde and 4% carboxylic t-BuOH oxidative system for 22 h at 607C, Rh Å 106

nm, polydispersity Å 1.40.acid. In fact, the products identified by 1H-NMRwere obtained from Soxhlet extraction with tetra-hydrofuran. Since the polymer was partially

crosslinked after oxidation, the 1H-NMR samplemight not reflect the actual yield and the totalproduct distribution. The thermal properties ofPMS and its oxidized derivative were determinedwith differential scanning calorimetry (DSC).The glass transition temperature (Tg ) of the PMSincreased from 87 to 1187C upon 24% oxidation,which may be due to the increase in polarity andpossible crosslinking.

The PMS latex particles were partially cross-linked after oxidation. The crosslink density ofthe insoluble part which swelled in toluene wasdetermined using the statistical theory of swell-ing of network polymer.18 The calculations indi-cated that every 210 monomer units might haveone crosslinking point. Soxhlet extraction of theoxidized polymer with toluene, THF, and metha-nol was used to isolate polymer that had notcrosslinked. The percentage gel was determinedby weighing the residue left inside the thimbleafter drying under reduced pressure. The gelcontents of the polymers obtained usingCo(OAc)2 and CuCl2 were 82% at 24% oxidationand 52% at 33% oxidation, respectively. Thus,the polymer obtained from the CuCl2 catalyzedoxidation had a higher degree of oxidation anda lower gel content. The crosslinking may haveoccurred via the coupling of methylene or alkoxy

(CH‹)‹COOH

n

x y

mπ

m x y z

x π y π z π

(CH‹)‹COOı 1 (CH‹)‹COı 1 H¤O

Co /Co

CH‹

CH‹

CH‹

CH‹ CH¤ CHO COOH

CH¤ CHO COOH

CH¤ı

II III

Co /Co

Coupling between two methylene radicals O¤ (Oxidation)

(CH‹)‹COOH 1 1 (CH‹)‹COH

II III

radicals. A possible reaction mechanism is pro-posed in Scheme 3.

Scheme 3. Mechanism of oxidation. It was very interesting to note that the hydro-



overcome the destability caused by the increasein particle size, thus enabling the oxidation to becarried out in a stable emulsion.

CONCLUSION

We have demonstrated that poly(methylstyrene)(PMS) latex particles bearing surface aldehydeand carboxylic acid groups can be prepared by theemulsion polymerization of 3(4)-methylstyrenein the presence of sodium dodecyl sulfonate, fol-lowed by an in-situ oxidation catalyzed by cop-per(II) chloride and t-butyl hydroperoxide in thepresence of t-butyl alcohol under air. This surfacefunctionalization method allows us to control theamounts of functional groups on the surface bycontrolling the degree of oxidation based on thereaction conditions. This method also has an ad-vantage in ease of purification of the function-alized latex particles because the use of water-soluble functional monomer is avoided. Finally,this method provides an alternative syntheticroute to the preparation of a potentially largeclass of functionalized latex particles, which mayfind many useful applications.

The authors thank Dr. Chi Wu for many helpful com-ments and discussion on the dynamic light scatteringexperiments. Financial support by the Hong Kong Poly-technic University is gratefully acknowledged.

Figure 6. Scanning electron micrographs of (a) the REFERENCES AND NOTESPMS latex particles, and (b) the oxidized PMS latexparticles.

1. C. Pichot, Polym. Adv. Technol., 6, 427 (1995).2. C. Pichot, B. Charleux, M. Charreyre, and J. Re-

villa, Macromol. Symp., 88, 71 (1994).dynamic radii (Rh ) and polydispersity index of the 3. A. Rembaum, M. Chang, G. Richards, and M. Li,polymer latex particles increased during the oxi- J. Polym. Sci. Polym. Chem., 22, 609 (1984).dation. For example, the average size of the PMS 4. A. Rembaum, R. C. K. Yen, D. H. Kempner, and J.latex particles changed from 74.8 to 212 nm in Ugelstad, J. Immunol. Methods, 52, 341 (1982).

5. C. Yan, X. Zhang, Z. Sum, H. Kitano, and N. Ise,diameter during the oxidation (Fig. 5). These re-J. Appl. Polym. Sci., 40, 89 (1990).sults were further confirmed by scanning electron

6. B. Charleux, P. Fanget, and C. Pichot, Makromol.microscopy as shown in Figures 6(a) and 6(b).Chem., 193, 205 (1992).The increase in particle size could be due to the

7. M. Okubo, Y. Kondo, and M. Takahashi, Colloidswelling caused by (i) the presence of the carbox-Polym. Sci., 271, 109 (1993).ylic acid groups on the surface, and (ii) the pres-

8. Q. Wang, S. K. Fu, and T. Y. Yu, Progress Polym.ence of the organic solvent. Although the size of Sci., 19, 703 (1994).the latex particles and polydispersity index in- 9. M. D. Bale Oenick and A. Warshawsky, Colloidcreased during the oxidation, the latex stability Polym. Sci., 269, 139 (1991).was retained because of the formation of increas- 10. H. G. Elias and F. Vohwinkel, New Commercial Poly-ing amounts of carboxylic acid groups on the parti- mer 2, Gordon and Breach, New York, 1986, p. 41.

11. R. A. Sheldon and J. K. Kochi, Metal-Catalyzed Ox-cle surface. The resulting surface charge could


1872 LI ET AL.

idation of Organic Compounds, Academic, New 15. G. Sosnovsky and D. J. Rawlinson, Organic Perox-ides, D. Swern, Ed., Interscience, New York, 1971,York, 1981.

12. L. P. Ferrari and H. D. H. Stover, Macromolecules, Vol. II, p. 269; 1972, Vol. III, p. 141.16. R. Hiatt, K. C. Irwin, and C. W. Gould, J. Org.24, 6340 (1991).

13. H. D. H. Stover, P. Li, L. P. Ferrari, R. T. Shaver, and Chem., 33, 1430 (1968).17. J. K. Kochi and R. V. Subramanian, J. Am. Chem.D. Vlaovic, U.S. Pat., 5,376,732, December 1994.

14. R. T. Shaver, D. Vlaovic, I. Reviakine, R. Wittaker, Soc., 87, 1508 (1965).18. A. Tager, Physical Chemistry of Polymers, Mir Pub-L. P. Ferrari, and H. D. H. Stover, J. Polym. Sci.

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Documents

Surface functionalization of polymer latex particles. I. Catalytic oxidation of poly(methylstyrene) latex particles in the presence of an anionic surfactant