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Synthesis and application of terpolymer bearing cyclic carbonate and cinnamoyl groups
Optical Materials 21 (2002) 331–335 www.elsevier.com/locate/optmat
Synthesis and application of terpolymer bearing cyclic carbonate and cinnamoyl groups S.Y. Park, H.Y. Park, H.S. Lee, S.W. Park, D.W. Park
*
Department of Chemical Engineering, College of Engineering, Pusan National University, Janjun-Dong, Kumjung-Ku, Pusan 609-735, South Korea
Abstract We propose the syntheses of photopolymer with pendant cinnamic ester and cyclic carbonate groups by the addition reaction of poly(glycidyl methacrylate-co-styrene) with CO2 and then with cinnamoyl chloride. Quaternary ammonium salts showed good catalytic activity for this synthesis. Photochemical reaction experiments revealed that terpolymer having cinnamate and cyclic carbonate groups has good photosensitivity, even in the absence of sensitizer. In order to expand the application of the obtained terpolymer, polymer blends with poly(methyl methacrylate) were prepared. Differential scanning calorimetry and optical clarity tests showed that the blends were miscible over the whole composition ranges. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 82.50; 82.35; 83.80.T Keywords: Blends; Photopolymer; Quaternary ammonium salt; Carbon dioxide; Cinnamoyl chloride
1. Introduction Synthesis of polymers carrying reactive functional groups has been an active field of research in polymer science in recent years. Polymers containing an, a,b-unsaturated carbonyl group undergo crosslinking upon irradiation with UV light and are used as photoresists to make large-scale integrated circuits, printing plates, photocurable coatings, photorecorders and photo-conductors etc. [1]. Several negative photo-resists which can be used in various applications because of the structural variety of their photofunctional groups as
*
Corresponding author. Tel.: +82-51-510-2399; fax: +82-51512-8563. E-mail address: [email protected] (D.W. Park).
well as their polymer backbones have been reported in the literature [2]. Polymers with pendant cinnamic ester groups, pendant chalcone, a-cyanocinnamic ester, and a-phenylmaleimide systems have been reported [3–5]. Poly(glycidyl methacrylate) and its copolymer were known as useful functional polymers [6,7]. The syntheses of polyesters by the addition reactions of epoxides with dicarboxylic acid chlorides have been reported [8,9]. It was considered that this method can be adapted to the synthesis of photosensitive polymers and the modification of the resulting polymers. We propose the syntheses of polymers with pendant cinnamic ester and cyclic carbonate groups by the addition reaction of poly(glycidyl methacrylate-co-styrene) [poly(GMA-co-St)] with CO2 and cinnamoyl chloride. The photochemical
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reactions of the resulting polymers were also studied. Finally, blends of obtained terpolymer with poly(methyl methacrylate) (PMMA) were prepared to study their miscibility.
2. Experimental A radical copolymer of glycidyl methacrylate [28.43 g (0.2 mol)] with styrene [10.42 g(0.1 mol)] [poly(GMA-co-St)] was prepared in DMSO (360 ml) using AIBN (0.39 g) as an initiator at 70 °C for 24 h under nitrogen atmosphere, then the solution was poured into distilled water to give a precipitate. Polymers were recovered using an excess of methanol, and dried in vacuum at 30 °C for 12 h. The synthesis of a copolymer [poly(DOMA-co-St)] from poly(GMA-co-St) and CO2 was carried out using tetrabutyl ammonium chloride. Reaction was started by stirring the solution under a slow stream of CO2 (10 ml/min), and continued for 5 h. The obtained polymer was purified by precipitation in distilled water. Finally, poly(DOMA-co-St) (5.43 g) was dissolved in 70 ml of sulfolane, and 4.69 g of cinnamoyl chloride and 0.5 g of TOAC were added to the solution. The mixture was stirred at 100 °C for 10 h, and then was poured into 700 ml of methanol, and dried in vacuum oven at 50 °C. The identification of poly(CNMA-coDOMA-co-St) was performed by IR and 1 HNMR spectroscopies. The synthesis of objective polymer, poly[3-chloro-2-cinnamoyloxy propyl methacrylate-co-(2-oxo-1,3 dioxolane-4-yl) methyl methacrylate-co-styrene] [poly(CNMA-co-DOMA-co-St)], is represented in Scheme 1.
In order to measure photochemical reaction of obtained polymer, polymer solution in tetrahydrofuran was casted on a glass plate and dried. The film on the plate was irradiated by a high pressure mercury lamp (Q-PANEL Co., UVC313) without a filter at a distance of 20 cm. The rates of disappearance of the absorptions of the C@C group at 1640 cm1 was measured by IR spectroscopy (ASI REACT IRe 1000). To prepare blend films, the weighed amounts of poly(CNMA-co-DOMA-co-St) and PMMA with a given composition were casted from 10 wt% solution in DMF. The films were dried under vacuum for 3 days at room temperature.
3. Results and discussion 3.1. Synthesis of terpolymer containing cinnamic ester and carbonate groups from poly(DOMAco-St) with cinnamoyl chloride The synthesis of poly(CNMA-co-DOMA-co-St) was carried out by the reaction of poly(DOMAco-St) with cinnamoyl chloride in sulfolane using TOAC. The characteristic peaks from 1 H-NMR analysis (DMSO-d6 ) are as follows: 4.0–4.4 (–OCH2 –, in side chain), 4.4–4.8 (–OCH2 –, in cyclic carbonate), 4.9–5.2 (–HCO–, in cyclic carbonate), 6.5,7.6 (–CH@CH–, in cinnamoyl units), 7.4 (aromatic protons in cinnamoyl units), 6.7–7.2 ppm (aromatic protons in styrene). The conversions of GMA units to DOMA and CNMA units were 33.3% and 8.34%. The IR spectrum also confirmed the synthesis of poly(CNMA-co-DOMA-co-St). The spectra showed absorptions at 1800 cm1 (C@O of carbonate groups), at 1730 cm1 (C@O of cinnamoyl groups), at 1640 cm1 (C@C of cinnamoyl groups), and at 705 cm1 (C–Cl stretching). The disappearance of the absorption due to epoxide ring at 910 cm1 is also shown in Fig. 1. 3.2. Photochemical reaction of the obtained polymer
Scheme 1.
The photocrosslinking reaction of poly (CNMA-co-St) was studied on thin films in tetrahydrofuran solution (0.02%; 3 3 cm2 glass plate) in the absence of photosensitizer. Samples were
S.Y. Park et al. / Optical Materials 21 (2002) 331–335
333
tion destroys conjugation in the entire p-electron system, the IR absorption intensity decreases with irradiation time [10,11]. The rate of disappearance of absorption band due to the C@C of the cinnamic ester of the polymer was followed using the expression: Conversion of –C@C– ð%Þ ¼ 100 ½ðA0;–C@C– =A0;–CO– Þ ðA–C@C– =A–CO– Þ=ðA0;–C@C– =A0;–CO– Þ;
Fig. 1. IR spectra of poly(CNMA-co-DOMA-co-St) and poly(GMA-co-St).
irradiated with a high pressure mercury lamp in the presence of air. The changes in the IR spectral pattern of the polymer are presented in Fig. 2. Initially, the polymer shows an IR absorption band at 1636 cm1 due to C@C stretching of cinnamic ester. The irradiation resulted in a fast decrease of the absorption at 1636 cm1 , and the absorption almost completely disappeared within 24 h of irradiation. This behavior clearly indicates crosslinking of the polymer chains through 2p þ 2p cycloaddition of the C@C group of the pendant cinnamoyl units. Because the 2p þ 2p cycloaddi-
where, A0;–C@C– and A–C@C– are absorption peak area (after baseline correction) due to C@C of the cinnamic ester (1636 cm1 ) after irradiation times t ¼ 0 and T, respectively. A0;–CO– and A–CO– are absorption peak area due to C@O (1730 cm1 ) after irradiation times t ¼ 0 and T, respectively. In the polymer film, photoconversion values of about 66.9% and 100% were reached after 6 h and 24 h of irradiation. From these results, it is concluded that poly(CNMA-co-St) prepared by the addition reaction of poly(GMA-co-St) with cinnamoyl chloride has good photosensitivity, even in the absence of sensitizer. 3.3. Preparation of blend films Blends of poly(CNMA-co-DOMA-co-St) and PMMA were prepared by the solution-casting method. In order to examine the degree of miscibility of the poly(CNMA-co-DOMA-co-St)/ PMMA blends, optical clarity was first investigated (Table 1). All blends containing poly(CNMA-co-DOMA-co-St) formed clear films, which seems to mean that the blends are miscible
Table 1 Optical clarity test and glass transition temperature of poly(CNMA-co-DOMA-co-St)/PMMA blends
Fig. 2. The changes in the IR spectral patterns of the poly(CNMA-co-St) by UV irradiation.
Composition of poly(CNMA-co-DOMA-co-St)
Optical clarity
Tg (°C)
0.0 0.2 0.4 0.6 0.8 1.0
– Clear Clear Clear Clear –
114 78 74 52 53 49
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S.Y. Park et al. / Optical Materials 21 (2002) 331–335
viation in the Tg composition curve. The second aspect is in connection with the destruction of selfassociation which gives a positive contribution to free volume that should be taken into account. Consequently, Tg behavior is the result of a balance between the two factors considered above.
4. Conclusion
Fig. 3. Glass transition temperatures of poly(CNMAco-DOMA-co-St)/PMMA blends as a function of poly(CNMAco-DOMA-co-St) weight fraction.
over the whole concentration ranges. For the detailed study of polymer miscibility, we measured the glass transition temperatures of the blends. Each blend of different poly(CNMA-co-DOMAco-St) compositions with PMMA exhibited a single glass transition temperature between the two Tg s of each polymer. This result again confirms that these blends are miscible over the entire composition ranges. Fig. 3 shows the Tg values of the blends with different poly(CNMA-co-DOMA-co-St) weight fractions. The solid line represents the Tg of the blends estimated by the Fox equation [12], where the enthalpy of mixing is neglected (WA and WB are the weight fractions of A and B components, respectively): 1 WA WB ¼ þ Tg TgA TgB This composition dependence of the experimental data gives a slightly negative deviation relative to the Fox equation. The result suggests that there is a specific interaction between poly(CNMA-co-DOMA-co-St) with PMMA blends. This behavior may hint two different aspects [13,14]. First, the existence of strong hydrogen bonding between the two different polymer chains in the blend contributes to reduce the free volume and consequently to decrease the miscibility in the polymer blend; this would provoke a positive de-
Terpolymer containing cinnamoyl and carbonate groups was synthesized by using quaternary ammonium salts. The formation of the polymer was confirmed by FT-IR and 1 H-NMR spectra. The photo-crosslinking reaction of obtained polymer was studied on thin films in tetrahydrofuran solution by using a high pressure mercury lamp. In the polymer film, photoconversion values about 66.9% and 100% were reached after 6 and 24 h of irradiation. An integrated process has been developed for the catalytic conversion of carbon dioxide and cinnamoyl chloride to useful polymer materials by blending of poly(CNMA-co-DOMA-co-St) with PMMA. It was found that the blends of the terpolymer containing cinnamoyl and carbonate groups with PMMA were miscible over the whole composition ranges.
Acknowledgement This work was supported by the Korea Science and Engineering Foundation (KOSEF 20002-30700-002-3).
References [1] G. Nagamatzu, H. Inui, Photosensitive Polymers, Kodansha, Tokyo, 1977. [2] K. Ichimura, A. Kameyama, K. Hayashi, J. Appl. Polym. Sci. 34 (1987) 2747. [3] M. Kato, T. Ichijo, K. Ishii, M. Hasegawa, J. Polym. Sci. Part A––1 9 (1971) 2109. [4] C.C. Unruh, A.C. Smith, J. Appl. Polym. Sci. 3 (1960) 310. [5] T. Nishikubo, T. Ichijyo, T. Takaoka, J. Appl. Polym. Sci. 18 (1974) 2009. [6] N. Kihara, T. Endo, Macromolecules 25 (1992) 4824.
S.Y. Park et al. / Optical Materials 21 (2002) 331–335 [7] S.Y. Park, H.S. Lee, C.S. Ha, D.W. Park, J. Appl. Polym. Sci. 81 (2001) 2161. [8] T. Nishikubo, T. Iizawa, Y. Saito, J. Polym. Sci., Polym. Chem. 21 (1983) 2291. [9] K. Funahashi, Makromol. Chem. 180 (1979) 501. [10] T. Nishikubo, T. Iizawa, M. Yamada, J. Polym. Sci., Polym. Lett. 19 (1981) 177.
335
[11] K. Subramanian, V. Krichnasamy, S. Nanjundan, A.V. Rami Reddy, Polym. Int. 49 (2000) 579. [12] G. Chen, Nature 49 (1995) 373. [13] W.J. Macknight, M. Yang, J. Polym. Sci., Polym. Symp. 42 (1973) 817. [14] D. Garcia, H.W. Starkweather, J. Polym. Sci., Polym. Phys. 23 (1985) 537.
Synthesis and application of terpolymer bearing cyclic carbonate and cinnamoyl groups S.Y. Park, H.Y. Park, H.S. Lee, S.W. Park, D.W. Park
*
Department of Chemical Engineering, College of Engineering, Pusan National University, Janjun-Dong, Kumjung-Ku, Pusan 609-735, South Korea
Abstract We propose the syntheses of photopolymer with pendant cinnamic ester and cyclic carbonate groups by the addition reaction of poly(glycidyl methacrylate-co-styrene) with CO2 and then with cinnamoyl chloride. Quaternary ammonium salts showed good catalytic activity for this synthesis. Photochemical reaction experiments revealed that terpolymer having cinnamate and cyclic carbonate groups has good photosensitivity, even in the absence of sensitizer. In order to expand the application of the obtained terpolymer, polymer blends with poly(methyl methacrylate) were prepared. Differential scanning calorimetry and optical clarity tests showed that the blends were miscible over the whole composition ranges. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 82.50; 82.35; 83.80.T Keywords: Blends; Photopolymer; Quaternary ammonium salt; Carbon dioxide; Cinnamoyl chloride
1. Introduction Synthesis of polymers carrying reactive functional groups has been an active field of research in polymer science in recent years. Polymers containing an, a,b-unsaturated carbonyl group undergo crosslinking upon irradiation with UV light and are used as photoresists to make large-scale integrated circuits, printing plates, photocurable coatings, photorecorders and photo-conductors etc. [1]. Several negative photo-resists which can be used in various applications because of the structural variety of their photofunctional groups as
*
Corresponding author. Tel.: +82-51-510-2399; fax: +82-51512-8563. E-mail address: [email protected] (D.W. Park).
well as their polymer backbones have been reported in the literature [2]. Polymers with pendant cinnamic ester groups, pendant chalcone, a-cyanocinnamic ester, and a-phenylmaleimide systems have been reported [3–5]. Poly(glycidyl methacrylate) and its copolymer were known as useful functional polymers [6,7]. The syntheses of polyesters by the addition reactions of epoxides with dicarboxylic acid chlorides have been reported [8,9]. It was considered that this method can be adapted to the synthesis of photosensitive polymers and the modification of the resulting polymers. We propose the syntheses of polymers with pendant cinnamic ester and cyclic carbonate groups by the addition reaction of poly(glycidyl methacrylate-co-styrene) [poly(GMA-co-St)] with CO2 and cinnamoyl chloride. The photochemical
0925-3467/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 3 4 6 7 ( 0 2 ) 0 0 1 5 9 - 3
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S.Y. Park et al. / Optical Materials 21 (2002) 331–335
reactions of the resulting polymers were also studied. Finally, blends of obtained terpolymer with poly(methyl methacrylate) (PMMA) were prepared to study their miscibility.
2. Experimental A radical copolymer of glycidyl methacrylate [28.43 g (0.2 mol)] with styrene [10.42 g(0.1 mol)] [poly(GMA-co-St)] was prepared in DMSO (360 ml) using AIBN (0.39 g) as an initiator at 70 °C for 24 h under nitrogen atmosphere, then the solution was poured into distilled water to give a precipitate. Polymers were recovered using an excess of methanol, and dried in vacuum at 30 °C for 12 h. The synthesis of a copolymer [poly(DOMA-co-St)] from poly(GMA-co-St) and CO2 was carried out using tetrabutyl ammonium chloride. Reaction was started by stirring the solution under a slow stream of CO2 (10 ml/min), and continued for 5 h. The obtained polymer was purified by precipitation in distilled water. Finally, poly(DOMA-co-St) (5.43 g) was dissolved in 70 ml of sulfolane, and 4.69 g of cinnamoyl chloride and 0.5 g of TOAC were added to the solution. The mixture was stirred at 100 °C for 10 h, and then was poured into 700 ml of methanol, and dried in vacuum oven at 50 °C. The identification of poly(CNMA-coDOMA-co-St) was performed by IR and 1 HNMR spectroscopies. The synthesis of objective polymer, poly[3-chloro-2-cinnamoyloxy propyl methacrylate-co-(2-oxo-1,3 dioxolane-4-yl) methyl methacrylate-co-styrene] [poly(CNMA-co-DOMA-co-St)], is represented in Scheme 1.
In order to measure photochemical reaction of obtained polymer, polymer solution in tetrahydrofuran was casted on a glass plate and dried. The film on the plate was irradiated by a high pressure mercury lamp (Q-PANEL Co., UVC313) without a filter at a distance of 20 cm. The rates of disappearance of the absorptions of the C@C group at 1640 cm1 was measured by IR spectroscopy (ASI REACT IRe 1000). To prepare blend films, the weighed amounts of poly(CNMA-co-DOMA-co-St) and PMMA with a given composition were casted from 10 wt% solution in DMF. The films were dried under vacuum for 3 days at room temperature.
3. Results and discussion 3.1. Synthesis of terpolymer containing cinnamic ester and carbonate groups from poly(DOMAco-St) with cinnamoyl chloride The synthesis of poly(CNMA-co-DOMA-co-St) was carried out by the reaction of poly(DOMAco-St) with cinnamoyl chloride in sulfolane using TOAC. The characteristic peaks from 1 H-NMR analysis (DMSO-d6 ) are as follows: 4.0–4.4 (–OCH2 –, in side chain), 4.4–4.8 (–OCH2 –, in cyclic carbonate), 4.9–5.2 (–HCO–, in cyclic carbonate), 6.5,7.6 (–CH@CH–, in cinnamoyl units), 7.4 (aromatic protons in cinnamoyl units), 6.7–7.2 ppm (aromatic protons in styrene). The conversions of GMA units to DOMA and CNMA units were 33.3% and 8.34%. The IR spectrum also confirmed the synthesis of poly(CNMA-co-DOMA-co-St). The spectra showed absorptions at 1800 cm1 (C@O of carbonate groups), at 1730 cm1 (C@O of cinnamoyl groups), at 1640 cm1 (C@C of cinnamoyl groups), and at 705 cm1 (C–Cl stretching). The disappearance of the absorption due to epoxide ring at 910 cm1 is also shown in Fig. 1. 3.2. Photochemical reaction of the obtained polymer
Scheme 1.
The photocrosslinking reaction of poly (CNMA-co-St) was studied on thin films in tetrahydrofuran solution (0.02%; 3 3 cm2 glass plate) in the absence of photosensitizer. Samples were
S.Y. Park et al. / Optical Materials 21 (2002) 331–335
333
tion destroys conjugation in the entire p-electron system, the IR absorption intensity decreases with irradiation time [10,11]. The rate of disappearance of absorption band due to the C@C of the cinnamic ester of the polymer was followed using the expression: Conversion of –C@C– ð%Þ ¼ 100 ½ðA0;–C@C– =A0;–CO– Þ ðA–C@C– =A–CO– Þ=ðA0;–C@C– =A0;–CO– Þ;
Fig. 1. IR spectra of poly(CNMA-co-DOMA-co-St) and poly(GMA-co-St).
irradiated with a high pressure mercury lamp in the presence of air. The changes in the IR spectral pattern of the polymer are presented in Fig. 2. Initially, the polymer shows an IR absorption band at 1636 cm1 due to C@C stretching of cinnamic ester. The irradiation resulted in a fast decrease of the absorption at 1636 cm1 , and the absorption almost completely disappeared within 24 h of irradiation. This behavior clearly indicates crosslinking of the polymer chains through 2p þ 2p cycloaddition of the C@C group of the pendant cinnamoyl units. Because the 2p þ 2p cycloaddi-
where, A0;–C@C– and A–C@C– are absorption peak area (after baseline correction) due to C@C of the cinnamic ester (1636 cm1 ) after irradiation times t ¼ 0 and T, respectively. A0;–CO– and A–CO– are absorption peak area due to C@O (1730 cm1 ) after irradiation times t ¼ 0 and T, respectively. In the polymer film, photoconversion values of about 66.9% and 100% were reached after 6 h and 24 h of irradiation. From these results, it is concluded that poly(CNMA-co-St) prepared by the addition reaction of poly(GMA-co-St) with cinnamoyl chloride has good photosensitivity, even in the absence of sensitizer. 3.3. Preparation of blend films Blends of poly(CNMA-co-DOMA-co-St) and PMMA were prepared by the solution-casting method. In order to examine the degree of miscibility of the poly(CNMA-co-DOMA-co-St)/ PMMA blends, optical clarity was first investigated (Table 1). All blends containing poly(CNMA-co-DOMA-co-St) formed clear films, which seems to mean that the blends are miscible
Table 1 Optical clarity test and glass transition temperature of poly(CNMA-co-DOMA-co-St)/PMMA blends
Fig. 2. The changes in the IR spectral patterns of the poly(CNMA-co-St) by UV irradiation.
Composition of poly(CNMA-co-DOMA-co-St)
Optical clarity
Tg (°C)
0.0 0.2 0.4 0.6 0.8 1.0
– Clear Clear Clear Clear –
114 78 74 52 53 49
334
S.Y. Park et al. / Optical Materials 21 (2002) 331–335
viation in the Tg composition curve. The second aspect is in connection with the destruction of selfassociation which gives a positive contribution to free volume that should be taken into account. Consequently, Tg behavior is the result of a balance between the two factors considered above.
4. Conclusion
Fig. 3. Glass transition temperatures of poly(CNMAco-DOMA-co-St)/PMMA blends as a function of poly(CNMAco-DOMA-co-St) weight fraction.
over the whole concentration ranges. For the detailed study of polymer miscibility, we measured the glass transition temperatures of the blends. Each blend of different poly(CNMA-co-DOMAco-St) compositions with PMMA exhibited a single glass transition temperature between the two Tg s of each polymer. This result again confirms that these blends are miscible over the entire composition ranges. Fig. 3 shows the Tg values of the blends with different poly(CNMA-co-DOMA-co-St) weight fractions. The solid line represents the Tg of the blends estimated by the Fox equation [12], where the enthalpy of mixing is neglected (WA and WB are the weight fractions of A and B components, respectively): 1 WA WB ¼ þ Tg TgA TgB This composition dependence of the experimental data gives a slightly negative deviation relative to the Fox equation. The result suggests that there is a specific interaction between poly(CNMA-co-DOMA-co-St) with PMMA blends. This behavior may hint two different aspects [13,14]. First, the existence of strong hydrogen bonding between the two different polymer chains in the blend contributes to reduce the free volume and consequently to decrease the miscibility in the polymer blend; this would provoke a positive de-
Terpolymer containing cinnamoyl and carbonate groups was synthesized by using quaternary ammonium salts. The formation of the polymer was confirmed by FT-IR and 1 H-NMR spectra. The photo-crosslinking reaction of obtained polymer was studied on thin films in tetrahydrofuran solution by using a high pressure mercury lamp. In the polymer film, photoconversion values about 66.9% and 100% were reached after 6 and 24 h of irradiation. An integrated process has been developed for the catalytic conversion of carbon dioxide and cinnamoyl chloride to useful polymer materials by blending of poly(CNMA-co-DOMA-co-St) with PMMA. It was found that the blends of the terpolymer containing cinnamoyl and carbonate groups with PMMA were miscible over the whole composition ranges.
Acknowledgement This work was supported by the Korea Science and Engineering Foundation (KOSEF 20002-30700-002-3).
References [1] G. Nagamatzu, H. Inui, Photosensitive Polymers, Kodansha, Tokyo, 1977. [2] K. Ichimura, A. Kameyama, K. Hayashi, J. Appl. Polym. Sci. 34 (1987) 2747. [3] M. Kato, T. Ichijo, K. Ishii, M. Hasegawa, J. Polym. Sci. Part A––1 9 (1971) 2109. [4] C.C. Unruh, A.C. Smith, J. Appl. Polym. Sci. 3 (1960) 310. [5] T. Nishikubo, T. Ichijyo, T. Takaoka, J. Appl. Polym. Sci. 18 (1974) 2009. [6] N. Kihara, T. Endo, Macromolecules 25 (1992) 4824.
S.Y. Park et al. / Optical Materials 21 (2002) 331–335 [7] S.Y. Park, H.S. Lee, C.S. Ha, D.W. Park, J. Appl. Polym. Sci. 81 (2001) 2161. [8] T. Nishikubo, T. Iizawa, Y. Saito, J. Polym. Sci., Polym. Chem. 21 (1983) 2291. [9] K. Funahashi, Makromol. Chem. 180 (1979) 501. [10] T. Nishikubo, T. Iizawa, M. Yamada, J. Polym. Sci., Polym. Lett. 19 (1981) 177.
335
[11] K. Subramanian, V. Krichnasamy, S. Nanjundan, A.V. Rami Reddy, Polym. Int. 49 (2000) 579. [12] G. Chen, Nature 49 (1995) 373. [13] W.J. Macknight, M. Yang, J. Polym. Sci., Polym. Symp. 42 (1973) 817. [14] D. Garcia, H.W. Starkweather, J. Polym. Sci., Polym. Phys. 23 (1985) 537.