Sang-Hun Han, Kyung-Kyu Park, and Sang-Ho Lee* Department of Chemical Engineering, Dong-A University, Busan , Korea

Transcription

1 Mcromoleculr Reserch, Vol. 17, No. 1, pp (2009) Polymeriztion of Methyl Methcrylte in Crbon Dioxide Using Glycidyl Methcrylte Linked Rective Stbilizer: Effect of Pressure, Rection Time, nd Mixing Sng-Hun Hn, Kyung-Kyu Prk, nd Sng-Ho Lee* Deprtment of Chemicl Engineering, Dong-A University, Busn , Kore Received July 14, 2008; Revised August 25, 2008; Accepted August 25, 2008 Abstrct: Using glycidyl methcrylte-linked poly(dimethylsiloxne), methyl methcrylte ws polymerized in supercriticl CO 2. The effects of CO 2 pressure, rection time, nd mixing on the yield, moleculr weight, nd moleculr weight distribution (MWD) of the poly(methyl methcrylte) (PMMA) products were investigted. The shpe, number verge prticle dimeter, nd prticle size distribution (PSD) of the PMMA were chrcterized. Between 69 nd 483 br, the yield nd molr mss of the PMMA products showed trend of incresing with incresing CO 2 pressure. However, the yield leveled off t round 345 br nd the prticle dimeter of the PMMA incresed until the pressure reched 345 br nd decresed therefter. With incresing pressure, MWD becme more uniform while PSD ws unffected. As the rection time ws extended t 207 br, the prticle dimeter of PMMA decresed t 0.48 ± 0.03% AIBN, but incresed t 0.25% AIBN. Mixing the rectnt mixture incresed the PMMA yield by 18.6% nd 9.3% t 138 nd 207 br, respectively. Keywords: polymeriztion, supercriticl CO 2, mcromonomer, pressure effect, mixing. Introduction Since Sumitomo Chemicl Compny disclosed polymeriztion process of vinyl monomers in crbon dioxide in 1968, 1 gret number of studies hve been focused on polymeriztion of methyl methcrylte (MMA) in liquid nd supercriticl CO CO 2 is fundmentlly non-solvent for most polymers. For instnce, poly(methyl methcrylte) (PMMA) is insoluble in CO 2 even t 255 o C nd 2,550 br, wheres MMA nd its oligomers re dissolved t decent pressures. 8,9 As the polymeriztion proceeds, PMMA ctive chins re synthesized. Once the molr mss of the ctive chins exceeds certin limit, they fll out of the homogenous solution of CO 2 -MMA. Therefore, PMMA is synthesized vi precipittion polymeriztion without stirring nd surfctnt tht mke the growing chins stble in the continuous phse. Generlly, the surfctnts for the dispersion polymeriztion in CO 2 consist of two prts. One prt contins CO 2 -philic fluoro or silicone repet units in the bckbone or pending structures, wheres the other prt hs comptible components to growing polymers Some reserches used cosolvents with surfctnts to enhnce the stbility of the dispersion polymeriztion in CO 2. 14,15 Using rective surfctnt is nother pproch for the polymeriztion of vinyl monomers in supercriticl CO 2. Since *Corresponding Author. E-mil: sngho@du.c.kr Shffer et l. 16 used poly(dimethylsiloxne) monomethcrylte s surfctnt for polymeriztion of MMA nd styrene in supercriticl CO 2, PDMS mcromonomers hve been widely used s rective stbilizer for the dispersion polymeriztion in liquid nd supercriticl CO 2. For instnce, commercilly supplied PDMS mcromonomers, such s PDMS monomethcrylte, 7,14,16-19 monocrbinol-terminted PDMS, 14 PDMS-g-pyrrolidone crboxylic cid, 6 methcryloxypropyl-terminted PDMS, 20 nd vinyldimethylsiloxy PDMS, 21 were used for the dispersion polymeriztion of MMA nd styrene. Insted of using commercilly vilble mcromonomer stbilizer, Giles et l. synthesized PDMS monomethcrylte surfctnt from hexmethylcyclotrisiloxne nd 3-(methcryloxy)propyldimethylchlorosilne using lithium ctlyst. 19 They demonstrted the effect of the molr mss of their own surfctnts on the dispersion polymeriztion of MMA in CO 2. We prepred new rective stbilizer by linking glycidyl methcrylte (GMA) nd monoglycidyl ether terminted PDMS (MG-PDMS) using minopropyltriethoxysilne. The synthetic procedure requires no use of both solvent nd ctlyst. Since our procedure does not mke ny by-product, dditionl pretretment or purifiction process is not required. The resulted product, glycidyl methcrylte linked poly(dimethylsiloxne) (GMA-PDMS) hs both vinyl group nd CO 2 -philic group. Figure 1 shows the structure of GMA- PDMS. The detils to synthesize nd chrcterize GMA- 51

2 S.-H. Hn et l. Figure 1. The structure of GMA-PDMS stbilizer. PDMS re described in our previous pper. 22 Using GPC, the molr mss of MG-PDMS nd GMA- PDMS were determined to 5,500 nd 5,800, respectively. By dding the molr mss of minopropyltriethoxysilne nd GMA to the M n of MG-PDMS, the M n of GMA-PDMS stbilizer ws clculted to 5,884, which is lmost identicl to the M n mesured from GPC. The prepred GMA-PDMS ws used for dispersion polymeriztion of MMA in supercriticl CO 2. Our previous studies were focused on synthesizing GMA-PDMS nd investigting the effect of the stbilizer, inititor, nd monomer concentrtions on dispersion polymeriztion of MMA in supercriticl CO 2. In this pper, we demonstrted the effect of CO 2 pressure, rection time, nd mixing on the yield, molr mss, nd morphology of the PMMA products. Experimentl Mterils. MMA with minimum purity of 99% ws obtined from Junsei Chemicl Co. nd purified by vcuum distilltion. 2,2'-Azobisisobutyronitrile (AIBN) with minimum purity of 99% (Otsuk Chemicl Co. 99%+) ws recrystlized twice from methnol. Hexne (Aldrich, HPLC grde) nd toluene (CP grde, 99%+) were used s received. Crbon dioxide with purity of 99.99% ws obtined from Kore Stndrd Gs. Polymeriztion of MMA. Dispersion polymeriztion of MMA in supercriticl CO 2 ws crried out using highpressure, vrible-volume cell with working volume of 28 cm 3. The detils of experimentl pprtus, 23,24 nd the polymeriztion procedure re described in other references. 22 After the polymeriztion ws conducted for desired rection time, the cell ws cooled in dry ice bth. Then, the CO 2 in the cell ws completely relesed to tmospheric pressure. To remove unrected GMA-PDMS, PMMA product ws gitted in hexne for 24 h nd filtered. The filtered PMMA ws thoroughly dried for further nlysis. Chrcteriztion. The moleculr weight of PMMA product ws mesured using gel permetion chromtogrphy (Wters 150-C) with WATERS Styrgel mm column (HR2X1, HR3X1, HR4X1). Tetrhydrofurn ws used s the eluent. PS stndrds (Wters) were used to clibrte moleculr weight. A differentil refrctive index detector (Precision Detector Inc.) ws used to monitor the column output nd the dt were processed using WATERS GPC softwre (Millennium 2000). Scnning electron microscopy (SEM) imges were collected using HITACHI S-2400 SEM to chrcterize the morphology of PMMA product. The prticle dimeters of the PMMA product were verged from round one hundred individul prticles of ech SEM microgrph. Results nd Discussion Effect of Pressure. The dispersion polymeriztion of MMA in CO 2 is influenced by the solubility of MMA nd growing PMMA chins in CO 2. PMMA is not dissolved even t pressures greter thn 2,500 br, wheres MMA is soluble in CO 2 pressure of 120 br t 80 o C. 9 The solubility of MMA in supercriticl CO 2 cn be tuned by chnging CO 2 pressure tht is directly relted to CO 2 density. Therefore, the properties of the PMMA product re dependent on the CO 2 pressure. To investigte the effect of CO 2 pressure on Tble I. Effect of Pressure on Dispersion Polymeriztion of MMA No AIBN(wt%) Pressure (br) Yield (%) M n (g/mol) PDI b D nc (µm) PSD d Morphology , non-powder , powder , powder , powder , powder Number verge moleculr weight ws determined using GPC with PS stndrd. b PDI is polydispersity index (M w /M n ). c D n represents number verge dimeter of the PMMA prticle. d PSD represents prticle size distribution (D w /D n ). 52 Mcromol. Res., Vol. 17, No. 1, 2009

3 Polymeriztion of MMA in CO 2 Using GMA Linked Rective Stbilizer Figure 2. Effect of pressure on the yield nd number verge moleculr weight of the PMMA products polymerized in CO 2. The concentrtions of AIBN nd MMA were 0.51 ± 0.02 wt% nd 29.4 ± 0.7 wt%, respectively. The stbilizer concentrtion ws 5.4 ± 0.5 wt% bsed on the monomer weight. the PMMA product, the dispersion polymeriztion of MMA ws performed t vrious pressures between 69 nd 483 br. The polymeriztions were crried out t 80 o C for 4 h using 0.51 ± 0.02 wt% AIBN nd 29.4 ± 0.7 wt% MMA. The concentrtion of GMA-PDMS stbilizer ws 5.4 ± 0.5 wt% bsed on the monomer weight. Tble I summrizes the vrition of the yield, molr mss, nd morphology of the PMMA products with CO 2 pressures. Using the dt in Tble I (Run No 1~5), we plotted Figure 2 showing the effects of rection pressure on the yield nd the moleculr weight of PMMA products. MMA (30 wt%) - CO 2 (70 wt%) binry mixture seprtes into two phses, MMA- nd CO 2 -rich phse, t 80 o C nd pressures lower thn 105 br. 9 At pressures lower thn 105 br, the two phses exist in the rector t the initil stge of polymeriztion. As the polymeriztion proceeds there re three phses in the rector: MMA-rich phse, CO 2 -rich phse, nd the growing PMMA solid phse. Since most MMA exists in MMA-rich phse locted t low position of the rector, precipittion polymeriztion minly occurs during the rection. Thus, stble dispersion is not formed in the mixture of MMA, CO 2, nd the growing PMMA chin. It is expected tht the yield nd M n of PMMA product re low when the rection is crried out t pressures lower thn 105 br. Also the moleculr weight distribution will be wide. Tble I shows tht t 69 br, the PMMA with M n of 10,300 ws obtined in the yield of 87.4%. The M n nd the yield t 69 br were the lowest vlues in our experiments. The PMMA product ws recovered in non-powder form wheres the other ones t pressures higher thn 138 br were in powder form. Notice tht the PMMA synthesized t 69 br hs brod moleculr weight distribution. Since MMA is completely soluble in CO 2 t 138 br, MMA-CO 2 mixture is homogeneous t the initil stge of the polymeriztion. As the polymeriztion proceeds, growing PMMA chins or low moleculr weight PMMA re produced. Although PMMA is fundmentlly insoluble in CO 2, the solubility of the growing chin cn be enhnced by high CO 2 pressures. The growing PMMA will finlly fll out of the homogenous solution of MMA-CO 2 -PMMA when the molr mss of the PMMA chin exceeds certin vlue. However, the mixture in the rector forms the stble dispersions composed of MMA-CO 2 fluid phse nd the growing PMMA solid phse. Different from the PMMA product t 69 br, PMMA ws thoroughly obtined in micro-sphericl powder form. Figure 2 well demonstrtes tht the yield nd M n of the PMMA increse with the rection pressure. As the rection pressure incresed from 69 to 483 br, the yield incresed from 87.4 to 98.8 %. The M n lso incresed from 10,300 to 77,000, except the cse t 138 br. Compred with the polydispersity of PMMA polymerized t 69 br, the polydispersity chnged little t pressures higher thn 69 br. With the pressure incresing from 138 to 483 br, the polydispersity reduced from 2.4 to 1.9, suggesting tht the effect of CO 2 pressure on the moleculr weight distribution is limited once the rection pressure exceeds the criticl pressure of CO 2. Figure 3 shows the SEM imges of the PMMA prticles synthesized t different CO 2 pressures. The PMMA microsphere with dimeter of 2.8 µm ws obtined t the pressure of 138 br. As the pressure incresed to 207 nd 345 br, the number verge prticle size enlrged to 3.5 nd 4.8 µm, respectively. However, further incresing the pressure to 483 br reduced the PMMA prticle size little to 4.5 µm. While the verge prticle size incresed with CO 2 pressure, the prticle size distributions (PSD) of the PMMA products were constnt t 1.4~1.5, suggesting tht the PSD is not influenced by CO 2 pressure. Effect of Rection Time. To investigte the effect of rection time on the yield, molr mss, nd morphology of PMMA products, PMMA were polymerized for different periods t vrious AIBN concentrtions. The polymeriz- Mcromol. Res., Vol. 17, No. 1,

4 S.-H. Hn et l. Figure 3. SEM imges of PMMA products synthesized t vrious CO 2 pressure. (A) 138 br, (B) 207 br, 22 (C) 345 br, nd (D) 483 br. The GMA-PDMS concentrtion ws 5.4 ± 0.5 wt% bsed on the monomer weight. The concentrtions of AIBN nd MMA were 0.51 ± 0.02 wt% nd 29.4 ± 0.7 wt%, respectively. The SEM imge t 207 br, (B), ws obtined by Hn et l.. 22 tions were crried out t 80 o C nd 207 br using 28.9 ± 1.6 wt% MMA nd 5.7 ± 0.9 wt% GMA-PDMS. Since the rte of free rdicl polymeriztion is proportionl to the squre root of inititor concentrtion, the polymeriztion is extended to longer periods t low AIBN concentrtions. Tble II summrizes the polymeriztion conditions nd the properties of the PMMA products. As the rection time incresed from 3 to 8 h, the PMMA yield incresed from 85.6 to 97.7% t 0.48 wt% AIBN. The increse of the yield leveled off round 95~97% fter 4 h of the rection time. The M n of PMMA products shows similr pttern with respect to the rection time. When the polymeriztion ws mintined for 3 h, the low molr mss PMMA (M n = 17,000) ws produced in the low yield of 85.6%. The low yield nd M n were the consequence of the low extent of the rection, which indictes 3 h ws not enough to complete the polymeriztion. When the rection time ws extended to 4 h, the yield nd M n of PMMA product incresed to 94.4% nd 41,600, respectively. However, the polydispersity of the PMMA decresed with incresing rection time. When the rection time ws extended from 3 to 4 h, the polydispersity significntly reduced from 7.1 to 2.5. The polydispersity leveled off round 2.2~2.4 when the polymeriztion time exceeded 5 h. Figure 4, plotted using the dt listed in Tble II, demonstrtes the effects of rection time on the yield nd moleculr weight of PMMA products. When 0.48 wt% AIBN ws used, the yield nd M n of PMMA products were not influenced by the rection time once the rection time extended beyond 5 h. The yield of PMMA products decresed when AIBN concentrtion decresed from 0.48 to 0.25 wt%. At 0.25 wt% AIBN, the yield of PMMA polymerized for 4 h ws 66% which ws much lower thn the yield of PMMA polymerized t 0.48 wt% AIBN. To compenste the slow rection rte t 0.25 wt% AIBN, we extended the rection time to 6 h. Due to the longer rection time, the PMMA yield incresed to 92.9%. However, this yield ws still lower thn the yield obtined from the polymeriztion crried out for 4 h t 0.48 wt% AIBN. Incresing rection time to 8 h enhnced the PMMA yield to 95.6%, which ws lmost identicl to the yield t 0.48 wt% AIBN. When the polymeriztion ws crried out for sme period, the M n of PMMA product t 0.25 wt% ws 1.6~1.8 times higher thn the M n of the PMMA t 0.48 wt% AIBN, which well greed with our Tble II. Effect of Rection Time on Dispersion Polymeriztion of MMA Run No Rection Time (h) AIBN (wt%) Yield (%) M n (g/mol) PDI b c D n (µm) PSD d Morphology , powder , powder , powder , powder , powder , powder , powder , powder , non-powder , few powder Number verge moleculr weight ws determined using GPC with PS stndrd. b PDI is polydispersity index (M w /M n ). c D n represents number verge dimeter of PMMA. d PSD represents prticle size distribution (D w /D n ). 54 Mcromol. Res., Vol. 17, No. 1, 2009

5 Polymeriztion of MMA in CO 2 Using GMA Linked Rective Stbilizer Figure 4. Effect of rection time on the yield nd moleculr weight of the PMMA products polymerized t 207 br of CO 2. The concentrtions of MMA were 28.9 ± 1.6 wt%. The stbilizer concentrtion ws 5.7 ± 0.9 wt% bsed on the monomer weight. expecttion t low inititor concentrtion. We further reduced AIBN concentrtion to 0.13 wt%. Although the rection time ws extended to 16 h, the PMMA yield decresed to 21.4%. This decrese in the PMMA yield ws consistent with the results observed t 0.48 nd 0.25 wt% AIBN. If the rection is crried out for long period t 0.13 wt% AIBN, the highest molr mss of PMMA is expected to be produced. However, our experiment showed opposite results. The M n ws only 6,800 nd the polydispersity ws These results suggest tht t extremely low concentrtions of AIBN, the formtion of PMMA ctive chin is limited nd thus low moleculr weight of the PMMA is obtined in low yield. Figures 5 nd 6 show the vritions of PMMA morphology with the rection time t 0.25 nd 0.48 wt% AIBN. All PMMA products were obtined in powder form. At 0.25 wt% AIBN, the prticle dimeter incresed from 2.0 to 3.5 µm when the rection time incresed from 4 to 6 h. At low AIBN concentrtion, few PMMA ctive chins re formed. Therefore, one growing PMMA chin rects with mny MMA nd the dimeter of ech PMMA chin becomes lrger. As the rection time ws extended from 6 to 8 h the prticle dimeter incresed from 3.5 to 3.7 µm. This increse ws only 13.3% of the increse for extending the rection time from 4 to 6 h. After 6 h of rection time, more thn 92.9% of MMA ws converted nd smll mount of MMA ws left in the rector. Due to the smll mount of MMA, the increse of the prticle dimeter ws not pprent. At 0.48 wt% AIBN, the verge dimeter of PMMA product is expected to be smller thn t 0.25 wt% AIBN, since the number of MMA per one growing PMMA chin is smller thn t 0.25 wt% AIBN. The verge dimeter of PMMA ws 5.6 µm when the polymeriztion ws conducted for 3 h. Figure 6 shows tht s the rection ws proceeding, the prticle dimeter decresed nd becme smller thn the dimeter t 0.25 wt% AIBN. Since the M n nd yield of the PMMA hd incresed until the rection time reched Figure 5. SEM imges of PMMA products synthesized for (A) 4 h t 0.25 wt% AIBN, (B) 6 h t 0.25 wt% AIBN, 22 (C) 3 h t 0.46 wt% AIBN, (D) 4 h t 0.48 wt% AIBN, 22 (E) 5 h t 0.48 wt% AIBN, nd (F) 6 h t 0.48 wt% AIBN. The polymeriztion conditions nd the product properties re listed in Tble II. The SEM imges, (B) nd (D), were obtined by Hn et l.. 22 Mcromol. Res., Vol. 17, No. 1,

6 S.-H. Hn et l. Figure 6. Effect of rection time on the number verge prticle dimeter (D n ) of the PMMA products polymerized t 207 br. The concentrtions of MMA were 28.9 ± 1.6 wt%. The stbilizer concentrtion ws 5.7 ± 0.9 wt% bsed on the monomer weight. 5 h (Figure 4), we presupposed tht the prticle size would increse or be constnt with the rection time. However, the verge prticle size grdully reduced from 5.6 to 2.5 µm s the rection time incresed from 3 to 8 h. The decrese in the prticle size leveled off fter the rection time exceeded 5 h. We were unble to figure out the reson for this reduction t 0.48 wt% AIBN. Further investigtion is required to clrify this issue. When PMMA ws polymerized t 0.25 nd 0.48 wt% AIBN, the PSD decresed with the rection time except the cse tht the rection ws extended to 8 h t 0.51 wt% AIBN. The PSD reduced from 1.9 to 1.2 nd from 1.5 to 1.3 t 0.25 nd 0.48 wt% AIBN, respectively. With the leveled-off prticle dimeter, the reltively constnt PSD vlues indicte tht the prticle size of the PMMA becomes uniform with the rection time. Mixing Effect. In order to produce PMMA of uniform property, it is required to mintin stble dispersion between growing PMMA chins nd MMA-CO 2 mixture. Not only stbilizer but lso mixing plys n importnt role to mke stble dispersion of the mterils in the rector. At the beginning of the polymeriztion, MMA is dissolved t moderte pressures. However, s the polymeriztion proceeds, growing PMMA chins re seprted from the MMA-CO 2 solution. Efficient mixing is needed to prevent the produced PMMA from precipittion nd cogultion. Tble III summrizes the effect of mixing on the yield nd properties of PMMA products t two different CO 2 pressures. At CO 2 pressure of 138 br, when the rection ws performed without mixing, PMMA ws obtined in mixed form of powder nd solid mss. Most of the products were composed of the solid mss. The portion of powdery PMMA ws less thn 5% of the totl products. The M n of the solid nd powdery PMMA products were 102,900 nd 39,200, respectively. As polymeriztion proceeded without mixing, growing PMMA chins fell out of the solution nd settled down on the bottom of the rector. The PMMA chins rected through precipittion polymeriztion with MMA nd other PMMA chins. Therefore PMMA product hd high M n (102,900) nd brod moleculr weight distribution (3.2). The powdery PMMA hd lower molr mss (39,200) nd PDI (2.8). The totl yield of the PMMA product ws 74.8 wt%. When the rectnt ws mixed during the polymeriztion, PMMA product ws obtined entirely in powder form. The yield incresed to 93.4%. Mixing the rectnt incresed the PMMA yield by 18.6%. The M n nd PDI were 56,500 nd 2.4, respectively. The PMMA product hd lower M n thn the solid mss, but higher thn the powdery PMMA polymerized without mixing. It is obvious tht mixing leds the PMMA product to hve uniform molr mss in high yield. When polymerized without mixing t 207 br, the PMMA product hd M n of 57,900 nd ws obtined in the yield of 85.1%. Similr to the PMMA t 138 br without mixing, the PMMA product ws mixed form of powder nd solid mss. However, most of the PMMA were powders. When polymerized with mixing t 207 br, powdery PMMA ws produced nd the yield incresed to 94.4%. Mixing incresed the yield by 9.3% t 207 br. The increse in yield t 207 br ws hlf of the increse t 138 br. At high CO 2 pressure, growing PMMA chins re more soluble thn t low pressure. The high solubility enhnces the stbility of dispersion between the PMMA chins nd Tble III. Effect of Mixing on Dispersion Polymeriztion of MMA No Mixing Pressure (br) Yield (%) M b n (g/mol) PDI c D d n (µm) PSD e Morphology 15 x ,200 f 102,900 g few powder nd solid mss 2 o , powder 16 x ,900 h powder nd few solid mss 3 o , powder Rections were performed for 4 h t 80 o C using 0.5 ± 0.02 wt% AIBN nd 29.7 ± 0.3 wt% MMA. The concentrtion of GMA-PDMS ws 5.4 ± 0.5 wt% bsed on the monomer weight. b Number verge moleculr weight ws determined using GPC with PS stndrd. c PDI is polydispersity index (M w /M n ). d D n represents number verge dimeter. e PSD represents prticle size distribution (D w /D n ). f M n of the powdery PMMA. g M n of the solid mss PMMA. h M n of the powdery PMMA. 56 Mcromol. Res., Vol. 17, No. 1, 2009

7 Polymeriztion of MMA in CO 2 Using GMA Linked Rective Stbilizer MMA-CO 2 mixture, with the consequence tht the PMMA is produced in high yield. At low CO 2 pressure, the PMMA chins re less soluble nd the dispersion is less stble thn t high pressure. Therefore, mixing is more required t low pressure thn high pressure, which indictes the mixing effect on the yield is more distinguished t low CO 2 pressures thn high pressures. Summry We prepred new rective stbilizer by linking GMA nd MG-PDMS using minopropyltriethoxysilne. The synthetic procedure requires no use of both solvent nd ctlyst. In ddition, there is no by products, which mens ny pretretment or purifiction process is not needed. These chrcteristics could be beneficil to commercil process for dispersion polymeriztion in CO 2. Between 69 nd 483 br of CO 2, the yield, molr mss nd prticle dimeter of PMMA products incresed with CO 2 pressures. The yield nd prticle dimeter leveled off round t 345 br. As rection time ws extended from 4 to 8 h, the prticle dimeter of PMMA decresed from 5.6 to 2.5 µm t 0.49 wt% AIBN, wheres the dimeter incresed from 2.0 to 3.7 µm t 0.25% AIBN. The prticle dimeters ll leveled off round 6 h rection time. The mixing effect on the yield is more remrkble t low CO 2 pressures thn high pressures. Mixing the rectnt incresed the PMMA yield by 18.6% nd 9.3% t 138 nd 207 br, respectively. Acknowledgment. This study ws supported by reserch fund from Dong-A University. References (1) Sumitomo Chemicl Compny, Sumitomo Atomic Energy Industries, U.S. Pt. 3,522,228 (1970). (2) S. D. Smith, J. M. DeSimone, H. Hung, G. York, D. W. Dwight, G. L. Wilkes, nd J. E. McGrth, Mcromolecules, 25, 2575 (1992). (3) J. M. DeSimone, E. E. Mury, Y. Z. Menceloglu, J. B. McClin, T. J. Romck, nd J. R. Combes, Science, 265, 356 (1994). (4) Y. L. Hsio, E. E. Mury, nd J. M. DeSimone, Mcromolecules, 28, 8159 (1995). (5) C. Lepilleur nd E. J. Beckmn, Mcromolecules, 30, 745 (1997). (6) J. Y. Prk nd J. J. Shim, J. Supercriticl Fluids, 27, 297 (2003). (7) C. A. Mntelis, R. Brbey, S. Fortini, nd T. Meyer, Mcromol. Rect. Eng., 1, 78 (2007). (8) F. Rindfleisch, T. P. DiNoi, nd M. A. McHugh, J. Phys. Chem., 100, (1996). (9) M. Lor nd M. A. McHugh, Fluid Phse Equilibri, 157, 285 (1999). (10) K. K. Kpellen, C. D. Mistele, nd J. M. DeSimone, Mcromolecules, 29, 495 (1996). (11) D. A. Cnels nd J. M. DeSimone, Mcromolecules, 30, 5673 (1997). (12) H. M. Woods, C. Nouvel, P. Licence, D. J. Irvine, nd S. M. Howdle, Mcromolecules, 38, 3271 (2005). (13) M. R. Giles, R. M. T. Griffiths, A. Aguir-Ricrdo, M. M. C. G. Silv, nd S. M. Howdle, Mcromolecules, 34, 20 (2001). (14) M. Z. Ytes, P. S. Shh, K. P. Johnston, K. T. Lim, nd S. Webber, J. Colloid Interf. Sci., 227, 176 (2000). (15) Q. Xu, B. Hn, nd H. Yn, Polymer, 42, 1369 (2001). (16) K. A. Shffer, T. A. Jones, D. A. Cnels, nd J. M. DeSimone, Mcromolecules, 29, 2704 (1996). (17) M. L. O Neill, M. Z Ytes, nd K. P. Johnston, Mcromolecules, 31, 2838 (1998). (18) M. L. O Neill, M. Z. Ytes, nd K. P. Johnston, Mcromolecules, 31, 2848 (1998). (19) M. R. Giles, J. N. Hy, S. M. Howdle, nd R. J. Winder, Polymer, 41, 6715 (2000). (20) S. M. Klein, V. N. Mnohrn, D. J. Pine, nd F. F. Lnge, Colloid Polym. Sci., 282, 7 (2003). (21) R. Wng nd H. M. Cheung, J. Appl. Polym. Sci., 93, 545 (2004). (22) S. H. Hn, K. K. Prk, nd S. H. Lee, Mcromol. Res., 16, 120 (2008). (23) S. H. Lee, M. A. LoStrcco, B. M. Hsch, nd M. A. McHugh, J. Phys. Chem., 98, 4055 (1994). (24) S. H. Lee, J. Appl. Polym. Sci., 95, 161 (2005). Mcromol. Res., Vol. 17, No. 1,