Journal of Scientific & Industri al Research Vol. 60, April 200 I, pp 336-343

Microemulsion al1ld Conventional Emulsion Copolymerizations of Styrene with n-Butyl Methacrylate, and Characterization of the Copolymers

G V Ramana Reddy·

Polymer Di vision, Central Leather Research Institute, Adyar, Chen nai-600 020, India

T S Balaji and P Kannan

Departmenl of Chemistry, Anna Un iversi ty, Chennai-600 025, India

Received: 03 October 2000; accepted: 05 Janu ary 200 1

Microemulsion (ME) and conventional emulsion (CE) copolymerizati on of styrene (STY) wit h n-butyl methacry late (B MA ) wcre carried out at 70 "C under inert atmospherc with sodiumlauryl sulphate (SLS) as surfactant, n-hexanol (HA) as cosurfactant and potassi um persulphate (KPS) as the free rad ical initiator. Five monomer mixtures in the initi al reaction mi XtLi l'cs were uscd and the reactions were arrested at lower conversions. The copo lymers thus obtained were characterized by FTIR, NMR , TG/ DTA , GC and GPc. The monomer composit ion of the copolymers were evaluated from the 'HNM R spectral data. The reactiv­ity ratios for the ME and CE copolymerization of styrene (STY) (r

STY) with n-butyl me[hac rylate (BMA) (r

8M) as determined

by Fineman-Ross (F-R), Kelen-Tudbs (K-T) and Mayo-Lewis (M-LJ methods were 0.74±0.02 and 0.64±O.02, and 0.58±O.02 and 0.39 ±0.02, respecti ve ly.

Introduction

Copolymerization, widely used in the production of

commercia l polymers and in fundamenta l inves tigati ons

of structure-property re lations, is the most general and

powerful method of effecting systematic changes in po ly­

mer properti es. The reactivity rati os of a monomer pair

may depend to some extent upon the condi tions of the

reaction-temperature, solvent e nvironment, e mul s ion polymerisation, etc. The effect of solvents having differ­ent dielectric constants, so lubility parameters and dipole

moments has been studied and reported in the lite rature " 4. Complex formation or solvati on of one monomer by

the so lvent5.7, and preferentia l solvati on of the polymer

coil by one of the monomers causi ng he te roge neous repartition of the monomer mi xture in sol uti on ca lled bootstrap effect8. '1 could lead to the dependence of reac­

tion ve locity upon the nature of the so lvent.

In general , copolymerizations in emul sion y ie lded

reactivity ratios in substantial agreement wi th those de­termin ed in mass , so luti o n , o r so lve nt -non so lve nt

copolymerizati on I2. IJ. The apparent reacti vity reduced if one of the monome rs is quite water-solublel~ . 1 6. ln e mul­

s ion copo lymerisati on, monomers containing long a lkyl

* Author for correspondencc

groups may ex hibit reduced appa rent reacti vities due to low rate of diffus ion to the locus of polymerizati on.

The studies on copolymerizat ion by mi croemuls ion polymerization meth od are rare in the lite rature. How­

eve r , a few s tudi es o n th e m ic ro emulsion

copo lymerizati ons of v inyl monomers appeared re­centlyl 7. '9. The reactivity ratios of monomer pairs deter­

mined by microemulsion copo lym riza ti o n l8 differed from that of bulk20 and e muls ion copolymerization21.

Different copolymerization behav iou r observed in these

polymerizations can be attributed to different mono mer ratios in po lymeri zat ion locil8 19.

In the present stud y, the microemul sion and conve n­ti onal emulsion copo lymeri zations of' , tyrene and n-butyl

methacrry late were carried out at 70 DC with sodium lauryl sulphate as surfactant , n-hex ano l as cosurfactant and potassium persulphate as the free rad ical initiator. The copolymers prepared were characteri zed by FfIR, NMR, TG/OTA, GC and GPC techniques. The relative reac tiv­

ity ratios of these monomer pair for the microemul sion and conventi onal emuls ion copolymerizations were de­

termined by the graphical procedure" due to F ine man­Ross22 , Mayo-Lewis23 and Kelen-TudOs24, and then com­

pared with those reported in litet:ature.

REDDY el at.: MICROEMULSION & CONVENTIONAL EMULSION COPOLYMERIZATIO OF STYRENE 337

Materials and Methods

Materials

Monomers, n-butyl methacrylate (BMA) (LR, SOH Chemical s Ltd., Poole, England) and styrene (STY) (commercial grade, Shin Ho Petrochemical (India) Ltd. , Chennai-600 103, India) were washed with five per cent sodium hydroxide and then with distilled water. The washed monomers were dried over anhydrous sodium sulphate, and further purified by vacuum distillation under inert atmosphere in an all glass quickfit set up and

stored in a refrigerator at -5°C.

Potassium persulphate (KPS) (LR, s.dJine chern pvt. ltd., Boisar401 501 , India) , sodium lauryl sulphate (SLS) (LR, Central Drug House Pvt. Ltd. , Mumbai , India) , n­hexanol (HA) (AR, Central Dru g House Pvt. Ltd ., Mumbai , India) and hydroquinone (AR, s.dJine chem pvt. ltd ., Boisar 40 I 501, India) were used as supplied without further purification .

Acetone (AR, Fischer Inorganic & Aromatics Ltd ., Chennai, India), methanol (AR, Fischer Inorganic & Aromatics Ltd ., Chennai, India) , methyl ethyl ketone (AR, S.d. fine chem pvt. ltd. , Boisar 40 I 50 I , India) and dehydrated alcohol (ethanol) (Bengal Chemical s & Phar­maceuticals Ltd., Calcutta 700 054, India) were purified

as per the standard procedures.

Methods

Preparation of Micro emulsion Solutions of Monomer Mixtures

The monomer mixtures of STY and BMA along with HA in requisite quantities were solubilized in aqueous solution of sodium lauryl sulphate with a magnetic stir­rer bar by stirring for 45-50 min or until the solution became unifornl. The solution was allowed to attain equi­librium overnight (Table I) . Thi s microemulsion solu­tion of the monomers mixture was used for microemulsion (ME) and conventional emul sion (CE) copolymerization experiments . Five mixtures of monomers, keeping the total weight of monome~~ con­

stanr, were used in these recipes for ME and CE copolymerization experiments (Tables I and 2).

Table I-Microemul sion so lution of styrene and n-butyl methacrylate:

Water

Sodium lauryl sulphate

n-Hexanol

Total weight of the monomers mixture

75 mL

6.75 g

3.268 g

3.9 g

Microemulsion Copolymerization

Thirty mL of ME solution of monomers mixture (Table I) was taken in a 50 mL reaction tube and the ME copolymerization was calTied out under inert atmos­phere at 70 °C by initiating with 9. I x 10-4M KPS solu­tion. The copolymerization reaction was arrested at lower conversions with hydroquinone and the copolymer was precipitated with methanol. The precipitated copolymer was washed with ethanol to remove unreacted monomer and surfactant, and then with water to remove water solu­ble impurities. The washed copolymer was dried to con­stant weight in a vacuum oven at 60 °C.

Conventional Emulsion Copolymerization

The CE copolymerization of the monomer STY 1 BMA pair was carried out by taking 20 mL of the ME recipe (Table I) in a 50 mL reaction tube and by suppl y­ing excess monomers mixture of the same composition , initiated with 9.1 x 10-4M KPS solution at 70 °C under

inert atmosphere. The rest of the procedure was as de­scribed above for the ME copolymerization The CE copolymerization experiments were carried out for five mixtures of the monomers as given in Table 3.

Characterization of the Copolymers

FTIR Spectral analysis

The FTIR spectra of the copolymers were recorded on Nicolet Impact 400 IR Spectrophotometer by casting thin films of the copolymers from chloroform solutions between KBr windows of size 25x4 mm.

IH and I3CNMR Spectral Analysis

High resolution IH and 13CNMR spectra of the co­polymer samples were recorded at ambient temperature with Bruker MSL 300P, 300 MHz FT-NMR Spectrometer, using chloroform-d (CDCI

3) as solvent and

tetramethylsilane as the internal standard .

Pyrolysis Gas Chromatographic Analysis

The copolymer samples were analysed on us ing Hewlett Packard 5840A Gas Chromatographic Instru­ment attached with HP pyroprobe 18580B unit under following operating conditions: Pyroprobe, Interface temperature, 50 °C; Ramp, LOoC/ms ; Pyrolysis interval , 5 s; Final temperature, 500°C. The G C conditions were: Column, 6 1_1 OP OV 17 Chrome WHP 100/200; Column

338 J SCI IND RES VOL 60 APRIL 2001

Table 2-Mi croemuls ion copolymeri zati on of styrene with n-butyl methacrylate

S.No. f , I" z FI F2 ilSTY ilBMA ill-l , KJ/mg Co nversion , (STY) (BMA ) (STY) (BMA ) from GC, fro m GC, per cent

per cent per cent 0.26 19 0 .7381 0.2839 0.7 161 75.79 24.2 1 66.38 (at 309.80C) 33.06

192.83 (at 3600C) 206.53 (at 438.80C)

2 0.4251 0.5749 0.4658 0.5342 72.77 27.23 723.89 26 .04 3 0.5800 0 .4200 0.6940 0.3060 77.86 22.13 601.66 12.42 4 0.7205 0 .2795 0.7298 0.2702 86. 15 13.85 892.48 10.55 5 0.8244 0.1756 0.7829 0.2 17 1 86.34 ]3.66 724.95 10.60

f, and f2 are mole frac ti ons of STY and BMA in the initi al feeds F, and Fz are mole fractions of STY and BMA in the copo lymers de termined from ' I-INMR spectral data

Table 3-Conventi ona l emu lsion copo lymerizat ion of styrene with n-butyl methacrylate

S.No. f, (STY) I~ (BMA) FI (STY) F~ (BMA) ilSTY ilBMA ill-l , KJ/mg Conversion. from GC, from GC, per cent per cent per cent

0.2682 0.73 18 0. 3746 0.6254 73.83 26. 17 533 .1 7 36.2 2 0.4252 0.5748 0 .4798 0.5202 73.43 26.57 629.06 3 1. 5 3 0.5799 0.420 I 0.485 1 0 .5 149 72.40 27.60 477.33 38.3 4 0 .7204 0.2796 0.6902 0.3098 8 1.43 18.57 11 95.95 6. 15 5 0.8244 0. 1756 0.8702 0. 1298 83.80 16.20 822.94 6 .65

1"1 and I"z are mole fract ions o f STY and BM A in the initi al feed s F, and Fz are mole fractions o f STY and BMA in the copo lymers determined from 'I-INMR spec tral data

temperature, 160 DC, Nitrogen carrie r, 10 mLl24 s; In­jecti on port, 165 °C; and flO temperature, 290 °C.

TGIDTA Analysis

The copolymers of STY/BMA were analysed for thermal behaviour on Se iko TGIDTA 200 instrument in nitrogen atmosphere with a gas flow of 100 mLimin in the te mperature region of 30-600 "C at a heating rate o f 20 °C/min . a-Alumina was used as the reference on plati­

num pans.

Gel Permeation Chromatogl-aphy

The molecular weights of copolymers prepared with 50:50 (w/w) ratio of monomers were estimated by GPC , usin g WATERS unit interfaced with an IBM AT com­patible NEC computer and tetrahydrofuran as e luting

solvent.

Results and Discussion

IR Spectroscopy

Infrared spectroscopy is ex tensive ly used in the in­vestigati on of polymer structure and analys is o f the fun c-

tio nal g roups. The FTIR spectra of the copolymers pre­pared in the laboratory showed the asymmetric stretch­ing vibrations o f -CH, groups in the reg ion 2985-2994 c m-I

. The sy mmetric stretching vibrations of -CH, group seemed to overlap with the stre tc hing vibrations o f -CH, group in the reg ion 2952-2862 cm-I

. The IR absorptiol~ peaks in the region 2845-2852 c m-I mi ght be due to the sym metric stretching vibration s of -CH

2 group. The ab­

sorption band in the 1730-1720 cm-I reg ion is character­

istic of -C=O stretching vibrations and its overtone was observed near 3450 cm-I

. The ab orptio n band in the re­g ion 1451-1443 c m-I resulted from the bending vibra­tions of -CH1 group and the bending vibrations of -CH? group was found slightly in the higher region in the TR absorpti on spectra. The rocking vibrations of -CH? cou ld be observed in the region 757-755 c rn-I . The s k el~tal vi­brations of polymer hackbone, the -C-O-C-stre tc hing resonances and the absorption due to su lphate end groups appeared in the regions , 1148- 11 4 1 cm I , 1280-1 100 c n,­I and 1410- 1367 cm-I

, respective ly (Figure I).

The IR spectra also showed the characteri sti c ab­sorption bands of phenyl ring in the sty rene. The -C-C-

REDDY et al.: MICROEMULSION & CONVENTIONAL EMULSION COPOLYMERIZATION OF STYRENE 339

2000 Wavenumber (em-II

1000

Figure I-FTIR spectra of STY-SMA copolymers made by ( I) microemulsion eopolymcrisation (sample 3) and (2) COIl ­

ventional emulsion copolymerisation (sample 3)

stretching vibrations of phenyl ring appeared in the re­gion 1604-1590 em-I and the -C-H deformation vibra­tions of ring hydrogens were found in the region 770-730 em-I. The 3100-3000 em-I band is assigned to -C-H

stretching vibrations of ring hydrogens , and the over­tone and combination bands of -C-H deformation vibra­tions are found in the region 2000-1660 em-I.

lHNMR and 13CNMR Studies

Figures 2 and 3 are the typical IHNMR spectra of the copolymers, STY/BMA, prepared by ME and CE copolymerization. The proton NMR spectra of the co­polymers showed chemical shifts due to phenyl protons in the region 6.65-7.94 ppm, and the methyleneoxy (­OCH2-) protons of the BMA units in the copolymer in the region 3.40-3.89 ppm. The chemical shifts due to methine protons of STY units in the copolymers were observed in the region 3.02-3.11 ppm, and those due to methylene groups in the region 1.01 -2.42 ppm. The reso­nance peaks due to methyl groups in these copolymers appeared in the region 0.40-0.90 ppm. The area of the resonance peaks due to phenyl protons of the STY units in the copolymers was taken as 5ASTY, and the total area of the resonance peaks due to methine, methylene and methyl groups in the copolymers was taken as (3 ASTY + 12 ABMA). The mole fractions of STY units (F

STY) in the copolymers were obtained as ASTYI

(ABMA+ASTY) using area of the resonance peaks in

ppm

Figure 2-IH NMR spectrum of STY -SMA copolymer sample I made by microemulsion copolymerisation

ppm

Figure 3-1 H NMR spectrum of STY -SMA copolymer sam ple I made by conventional emul sion copolymersalion

the proton NMR spectra of STY/BMA copolymers (Ta­bles 2 and 3, Figures 2 and 3).

Figure 4 is a typical 13CNMR spectrum of the STY I BMA copolymer prepared by ME copolymerisation . The 13CNMR spectra of the copolymers prepared by ME and CE copolymerizations showed resonance peaks due to carbonyl groups in the region 176.00-178 . 11 ppm and the phenyl carbons of the STY units in the region 122.84-145 .67 ppm. The solvent (CDCI ,) peak appeared in the region 76.59-77.43 ppm. The ~hemical shifts due to methyleneoxy carbons in I:lCNMR spectra of the copoly­mers appeared in the region 63.92-64.55 ppm and those due to methyl groups of the copolymers appeared in the region 13 .68-19 .26 ppm The resonance signal s due to methine and methylene groups, and tertiary carbon at­oms of BMA units in the copolymers appeared in the reg ion 29 .9 1-52. 16 ppm.

Pyrolysis Study

The values obtained for comonomer compositi ons by pyrolysis GC deviated from those obtained from the !HNMR spectral data (Tables 2 and 3). It might be due to unreliable yields of STY and BMA units by un zip­ping of copolymer samples at pyrolysis temperature of

340 J SCI INO RES VOL 60 APRIL 200 1

240 ~

200 ppm

Figure 4-IJC MR spectrum of STY-BMA copolymer sample 4 made by mi croemulsioll copo lymeri satio ll

500 °C, and a lso due to the lack of compari son of peak areas with ca libration curves of copol ymers of known composition25.

26. Two copolymers of the same overall

composition might differ wide ly in the d istributi on of monomer units in th e polyme r mol ec ul e and th e pyrogram of a copo lymer has been reported to depend on the sequence- length di stribution26 (Figure 5).

TGfDTA Analysis

The TG/DTA ana lys is of the STY/BMA copo lymers prepared by ME copo lymerizati on in the temperature region of 30-600 DC, at 20 °C/min (Figure 6) showed that the endothermic decomposition of the copolymers appeared from 259.7-481.7 dc. T he thermogram of the copo lymer sa mple I (Table 2) with higher proportion of BMA showed three di stinct endothermic peaks at 309 .8, 360 and 438.8 °C respecti ve ly. Remaining copolymers showed al most sing le endothermic effec t from 29 1.9-447.7 dc. The energy value (llH) of the endothennic proc­esses are persented in Table 2. Minimum llH was ob­tained fo r the copolymer prepared with 50:50 (w/w) pro­portion of monomers (Table 2). The endothermic decom­position shifted to hi gher temperature regions with in­crease in STY proportion in the copo lymers . Slow endothermic processes at lower te mperatures, from 55.7-286.7 °C were also observed. The endothermic processes at lower temperature reg ions might be due to low te m­perature transitions, rupture of weak bonds and so lvent evaporation (Figure 6). The TG curves showed 100 per cent decomposition of copolymer samples 1-4, and the sample 5, with higher proportion of STY units , showsed 97.7 per cent decomposi tion .

t

co r--o

Start

1 .'0 '3 ,.--,

Figure 5-Pyrolys is gas chromatogram or STY -BMA copolymer (sample 4) made by microemul sion copolymerisatloll.

The DTA ana lysis of the copo lymers in the tempera­ture region 30-600 °C showed almost sing le endotherm ic peak fro m 286.7-444. 1 °C for a ll the samples. The llH va lues for the endothermic effects are reported in Table 3. Min imum energy va lue for e ndothermi c decompos i­tion was obta ined for the copolymer prepared with 50:50 (w/w ) co mp os ition o f mo no mers (Tabl e 3). T he e dothermic decompositions shifted to higher tempera­ture regions with the increase in STY proportion . S low endothermic processes were again recorded from 57. 1--262.8 dc. The TG curves showed 100 per cent decom­

position for samples 1-4, and the sample 5, w ith higher proportion of STY units, showed 99.3 per cent decom­pos ition.

REDDY el al. : MICROEMULS ION & CONVENTIONA L EMULSION COPOLYMERIZATION OF STYRE NE 341

0

-20

-40 ~ <!> I-

-60

- 8 0

- 100 0 200 400 600

Temp .·C (Heat ing )

Figure 6 - TG/DTA analys is of STY -S MA copo lymers made by microemulsion copo lymerisat ion. T he com­positi ons of STY and SMA in the copo lymers: ( I ) 0 .2839:0.7 16 1, (2) 0.4658 :0.5342, (3) 0.6940:0.3060, (4) 0.7298:0 .2702 , a nd (5) 0 .7829:0.2 17 1.

2

o

-2 u:-

-6

N u:­I

L-~ ____ L-__ ~ ____ ~ ____ ~ __ ~_8

-20 -16 -12 -8 -4 o f2( F -1)

2 ( 1- f,) F,

Figure 7-Fineman-Ross method to eva lu ate the reac ti vi ty ra­ti os of STY and SMA fo r (I) microemu lsion and (2 ) conventional emu lsion copolymerisation.

Gel Permeation Chromatogl"aphic Study

The molecul ar weig ht (M) of 50:50 (w/w) STY/ BM A co p o ly m e rs, pre pa re d by ME a nd CE copolymeri sati on as determined by gel pe rmeati on chromatography showed very large di fference- the Mw for the copolymer prepared by CE copolymeri zation was 14.4x 105, which is 9 times that of the copo lymer prepared by M E copolymeri zati on with Mw of I .6x lOs

- 0 ·4

o 0 ·8 1·6

Figure 8-Kelen-Tudos method to evalu ate the reactivi ty ratios of STY and S MA fo r ( I) microemul sion and (2) conventional emul sion copolymeri sati on.

3·0

2·0

1·0

2 ·0

0 ·1 0 ·3 0 ·5 0·7 09 1·1

rSlY

Figure 9-Mayo-Lew is method to evaluate the reactivity rati os for the microemu lsion copolymerisation of STY and SMA-sam­ples I , 2, 4 and 5.

It mi g ht be due to the mono me r sta rva ti on in the ME copo lymeri zati on reacti on medium _

Reactivity Ratios of the Monomer Pair, STY IBM A

Th e reac ti v it y ra ti os fo r th e M E a nd CE co po ly me ri za ti o ns of STY a nd BM A dete rmin ed by Fineman-Ross (F_R)22, M ayo-Lew is (M_L)2.1 and Kelen­T udos (K_T)24 methods are g iven in Table 4, and shown in F igures 7-9. The Ke len-Tudos meth od gave the reactiv ity rati os, rSTY and r1\1I.-L\ fo r the ME copolymeri zat ion of STY

342 J CI IND RES VOL 60 APRIL 2001

Table 4--Reactivity ratios of the monomers , styrene and n-butyl methacrylate

Polymerization method

Bulk27

Bulk2x

Bulk2x

Microemulsivn (present study)

Emulsion (present study)

Solvent in reaction medium

n-Hexano l

n-H exanol

Method of evalu-ation F-R

F-R M-L K-T F-R M-L K-T

and BMA, respectively as 0.74 and 0.64, and 0.58 and 0.39, for CE copolymerization respectively. The rSTy and r

BMA reported in literature for bulk copol ymeri zations27.

28 of STY and BMA varied slightly from those obtained under present study (Tab le 4). In the present study, the monomers and cosurfactant were mi sc ible which were sparingly so luble in water. HA employed as cosurfactant was misc ible with both the monomers , and hence, the concentrations of the monomers and HA in the aqueous phase might be less than those based on thermodynamic considerations29 . HA existed in ME particles along with the surfactant in the surface and in the core with the monomers . HA also existed in CE copolymerizat ion sys­tem that could partition in emulsion particles with sur­factant and with monomers in the core, and it was so lu­bi lized in the monomer particles as a separate phase. The ex istence of HA in the reaction med ia might bring about changes in reactivity rat ios compared to that in bulk copolymerization? (Table 4). The difference in reactiv­ity ratio values under ME and CE copolymerization of STY and BMA in the present study (Table 4) could be attributed to the differences of monomer partitioning in different phases (i e, emu lsion globules and aqueous phase) of the copolymerization systems employed in the present study' s. ,Y.

Conclusions

The deviation in composition of copolymers by GC from that by 'HNMR might be due to unreliable yields of STY and BMA units by unzipping of copolymers at pyrolysis temperature of 500 °C. The TGIDTA analysis of STY IBMA copolymer samples, prepared by ME and CE copolymerisation, showed shifts in the endothermic decomposition processes to higher temperature region with the increase of STY proportion in copo lymers. Mini­mum energy values ( ~H ) were record ed 1'01' th e

Temperature, rSTY '"SM A

"C

60 0.56 0.40 50 0.63 0.64 70 0.54 0.64 70 0.73 ±O.02 0.55 ±O.02

0.85 ±O.02 0.55 ±O.02 0.74±0.02 0.64 ±O.02

70 0.59 ±O.02 0.45 ±O.02 0.59 ±O.02 0.40 ±O.02 0.58 ±O.02 0.39 ±O.02

endothermic decompositions of the copo lymers made by ME and CE copolymerization with equal proporti on of monomers. The reactivity ratios of STY and BMA ob­tained under present study differred from those for bulk copolymerization reported in literature which might be due to the presence of n-hexanol in the reaction media. Diffe ren t reac tivity ratios obtained by ME and CE copolymerization were considered as due to differences in monomer partition ing in different phases of ME and CE copolymerization systems employed in the present study.

References Pri ce C C & Walsh J G, J PolYIII Sci, 6 (i (5 1) 239-242.

2 Sideridou-K arayannidou I & Seretoud i G, PolYlll er. 3S(l6) ( 1997) 4223-4228.

3 Rytte i A, J Appl PolYIII Sci, 45 ( 1992) 19 1 i - 191 R.

4 Ryttel A, J Appl PolYIII Sci, 67 (1998) 7 15-721.

5 Cais R E, Fanner R G, Hili 0 J T & O' Donneli J H, Macmlllol­w iles, 12 (1979) 835-839.

6 Barton J & Borsig E. COlIllJlexes iJ/ Fre(' Radical Cftellli.I·IIT (Elsevier, Amsterdam) 1988.

7 O'Driscoli K F, Monteiro M J & Klumperman B,.1 Po/nil Sci. Pal'! A: PolY' II Cftelll Ed. 35 ( 1997) 515-520.

R Pichot C, Guyot A & Strazielie C, J PolylJl Sci. Pal'! A: PolYIII Cft elll Ed, 17 (1979) 2269-228 1.

9 Harwood H J, Macrolllol Cftelll . Macl'OlIIol SWill' , 10/11 (19S7) 33 1-354.

10 Hili 0 J T, Lang A P, Munro P 0 & O' Donneli J H. EliI' Poh'lll ./, 28(4) (1992) 39 1-398.

II Kai m A, J Macl'OlIIol Sci-Pllre AIJpl Cftm /, A33(11) ( 1996) 17 11- 1722.

12 Smith W V, J Alii Chel/l Soc, 6S ( 1946) 2069-207 1 ; 70 (I lJ48) 2 177-2 179, 36953702.

i 3 Lewi s F M, Waliing C, Cummings W, Briggs E & Mayo F R . ./ Alii Chel/l Soc. 70 (1948) 1519-1523.

REDDY et al.: MICROEMULSION & CONVENTIONAL EMULSION COPOLYMERIZATION OF STYRENE 343

14 Fordyce R G & Chapin E C, JAm Chelll Soc , 69 ( 1947) 581; 70 ( 1948) 2489-2492.

15 Fordyce R G & Ham G E, J Am Chell! Soc, 69 ( 1947) 695; J

PolYIIl Sci, 3 ( 1948) 891-894.

16 Bataille P & Bourassa H, J Polym Sci, Part A: PolYIll Chelll

Ed, 27 ( 1989) 357-365.

17 Capek I & Jurani cova V, J Polym Sci, Part A: PolYIIl Chem

Ed, 34 ( 1996) 575-585.

18 Gan L M, .Lee K C, Chew C H, Ng S C & Gan L H, Macro­

molecules, 27 (1994) 6335-6340.

19 Xu X, Ge X, Zhang Z & Zhang M, PolYlll er. 39(22) ( 1998) 5321-5325 .

20 Kale L T, O' Driscoll K F, Dinan F J & Uebel J J, J PolYIII Sci, Part A: Polym Chelll Ed, 24 ( 1986) 3 145-3 149.

2 1 Goldwasser J M & Rudin A, J PolYIll Sci, Part A: Polwl! Chelll

Ed, 20(8) (1982) 1993-2006.

22 Fineman M and Ross S D, J Polym Sci,S ( 1950) 259-262.

23 Mayo F R & Lewis F M, JAm Chem Soc, 66 ( 1944) 1594-1601.

24 Kelen T & Tudbs F, J Macromol Sci-Chelll , A9(1) ( 1975) 1-27.

25 Stevens M P, Characterization and Analysis of PolYlllers hy Gas Chromatography (Marcel Dekker, Inc., New York ) ( 1969) pp 90, 95.

26 Slade P E Jr. & Jenkins L T, Techlliques and Methods of Poly­

Iller Evaluatioll , Vol. 2, Thermal Characterization Techlliques (Marcel Dekker. Inc., New York) ( 1970) pp 75 , 80.

27 Otsu T, Ito T & Imoto M, J PolYIl1 Sci, B3 ( 1965) 11 3-117.

28 Vanderhoff J W, in Monomeric Acrylic Esters edited by Ri ddle E H (Reinhold , New York) (1954) pp 94, Ref. 154.

29 Guo J S, EI-Aasser M S & Vanderhoff J W, J Polym Sci, Part A:

PolYIll Chem Ed, 27 ( 1989) 691-710.