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Block copolymerization and chain extension by using PAAm prepolymer initiated with Ce (IV)–malonic acid
PERGAMON
European Polymer Journal 35 (1999) 1747±1754
Block copolymerization and chain extension by using PAAm prepolymer initiated with Ce (IV)±malonic acid Candan Erbil Istanbul Technical University, Department of Chemistry, 80626 Maslak, Istanbul, Turkey Received 9 July 1998; accepted 2 October 1998
Abstract The synthesis of block copolymers of polyacrylonitrile (PAN)±polyacrylamide (PAAm) was carried out with the use of PAAm±malonic acid (MA) prepolymer, which was a product of a redox polymerization initiated with the cerium sulphate±(MA) redox pair. The eects of prepolymer concentration and daylight on the yield and molecular structure were interpreted by means of FTIR spectroscopy. Furthermore, this prepolymer along with ceric ammonium nitrate was also used to induce the radical polymerization of acrylamide, resulting in further chain extension. Both FTIR spectra and intrinsic viscosities of the samples showed that the chain extension of PAAm±MA with AAm was aected by temperature and prepolymer content. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction The number of end groups per polymer molecule and their nature help in building block copolymers. Macromolecules containing segments with dierent chemical structures and physico-chemical properties can be obtained from synthesizing prepolymers with appropriate end groups. There are many reports in the literature on the block copolymer synthesis. Initiation by a redox process is only one method used to obtain these types of polymers [1±4]. However, initiation by a polymer having functional end groups attached to the chains, resulting from redox polymerization, has not been investigated widely in the literature [5]. Redox systems are widely used as initiators in radical polymerization. Compared to other methods, they have the prime advantage of operating at very moderate temperatures. This means that the probability of side reactions can be minimized. Ce (IV) or permanganate coupled with a hydroxyl or carboxylic group containing reductant is the initiator most often used [6±9].
Polymerization products obtained in the presence of acrylic monomers are the molecules containing the reducing substrates as end groups of the polymer chains formed. In an earlier article, we have reported the results of a study on the preparation of acrylamide (AAm) and acrylonitrile (AN) polymers having dierent numbers of carboxyl groups at the ends of chains [10]. Malonic, tartaric and citric acids were used as reducing agents in those systems. Furthermore, in that work, a conductometric titration method has been used for quantitative determination of the carboxyl end groups of polymers. This article shows the results of the investigations of block copolymerization with AN and chain extension with AAm of the polyacrylamide prepolymer initiated by the malonic acid±Ce (IV) redox pair (PAAm±MA). The aim is to ®nd the eect of prepolymer content in the reaction mixture on molecular weight (in the case of chain extension), molecular structure and yield of the synthesis.
0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 8 ) 0 0 2 8 2 - 1
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2. Experimental 2.1. Reagents Malonic acid (MA, HOOC0CH20COOH), ceric sulphate (Ce(SO4)2.4H2O), ceric ammonium nitrate ((NH4)2 Ce (NO3)6), acrylamide (AAm, CH21CH0CONH2), N, N-dimethyl formamide (DMF), sulphuric acid and nitric acid were all Merck quality and were used as supplied. Acrylonitrile (AN, CH21CH0CN) was washed successively with dilute H2SO4, Na2CO3 and water. After drying with Na2SO4, it was distilled repeatedly in N2 and stored at 58C in a refrigerator. All solutions used during the experimental work were prepared in distilled deonized water. 2.2. Experimental procedure Polymerizations were carried out in the presence of atmospheric oxygen. For the experiments, which were performed in the absence of light, the reaction vessel, as a whole, was covered with a black cloth. PAAm± MA prepolymer was prepared by redox polymerization in aqueous medium from ceric sulphate and malonic acid as described previously [10]. An appropriate solution of ceric ammonium nitrate in its respective acid was added to the aqueous solution of AAm (for chain extension) or AN (for block copolymerization) containing ®xed amounts of puri®ed PAAm±MA prepolymer. For all the polymerization experiments, a pyrex ¯ask equipped with a stirrer was
used. Both suspended copolymer, which was not precipitated from the reaction mixture during the synthesis, and PAAm obtained by chain extension of prepolymer were poured into a large excess of acetone, ®ltered o, washed with water and dried to constant weight. 2.3. Characterization Intrinsic viscosities of dilute solutions of AAm polymers in water were measured at 308C by use of an Ubbelohde suspended-level dilution viscometer. The relationship [Z] = 6.8010 ÿ 4M 0.66 was used to calculate the average molecular weights [11]. FTIR spectra were recorded using a Mattson 1000 Fourier transform IR spectrophotometer. The transmission mode was used on ®nely powdered samples prepared as KBr pellets. 3. Results and discussion From the relations between experimental conditions and FTIR spectra of the samples, the following reaction scheme is suggested for preparations of PAAm± MA prepolymer, chain extension of PAAm±MA with AAm, balances between polymer molecules and various metal complexes in the reaction media, gelation in the case of AAm polymerization at high temperatures, and block copolymerization of AN with prepolymer. The synthesis of AAm prepolymer was carried out using a redox system consisting of Ce(SO4)2.4H2O and MA.
C. Erbil / European Polymer Journal 35 (1999) 1747±1754
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the chains. The bands in the ranges of 550±650, 1100± 1200 and 1350±1450 cm ÿ 1 in the spectra of samples 2, 3 and 4 correspond to the metal±ligand complexes, and interaction of the amide groups with the complexes of Ce(IV) or Ce (III) with sulphate and nitrate or ÿ) ions such as Ce (SO4)n x(+ or ÿ) and Ce (NO3)x(+ , n respectively. The chain extension part of the polymerization mechanism can be shown by the following scheme:
The obtained prepolymer was examined by means of viscometric measurement and FTIR spectroscopy. The results of the measurements are given in Table 1 and illustrated in Fig. 1. From the comparison of the FTIR spectrum of this prepolymer with samples of PAAm initiated by K2S2O8 and (NH4)2 [Ce (NO3)6], it was observed that both Ce(IV) and anions of the salts could form complexes with the repeating units and the end groups of
Table 1 Aqueous polymerization of acrylamide initiated by various initiators at dierent temperatures Initiator
Sample no. in Fig. 1
Temperature (8C)
Product
Yield (g/50 ml)
[Z] (dl g ÿ 1)
Molecular weight
K2S2O8 MA±Ce(SO4)2.4 H2Oa (NH4)2 [Ce(NO3)6]b PAAm initiated with K2S2O8 (2.510 ÿ 3 g/50 ml) PAAm initiated with K2S2O8 (2.510 ÿ 3 g/50 ml.)
1 2 3 4
25 25 50 50
PAAm PAAm±MA prepolymer PAAm±Ce PAAm
± ± 0.67 0.30
± 0.16 0.48 0.18
02.0106 3.9103 2.1104 4.7103
±
30
±
±
±
±
a b
[MA] = 2.2210 ÿ 2 mol l ÿ 1; [Ce(IV)] = 2.2210 ÿ 2 mol l ÿ 1; [H2SO4] = 22.510 ÿ 2 mol l ÿ 1; [AAm] = 0.60 mol l ÿ 1; t = 1 h. [Ce(IV)] = 310 ÿ 3 mol l ÿ 1; [HNO3] = 0.20 mol l ÿ 1; [AAm] = 1.55 mol l ÿ 1; t = 2 h.
Table 2 Chain extension of PAAm±MA prepolymer with AAm in water Prepolymer (g/50 ml)
Sample no. in Fig. 2
Temperature (8C)
Yield (g/50 ml)
0.25 0.50 1.00 1.00 1.00
1 2 3 4 5 6
40 40 40 30 50
0.62 2.21 4.34 2.87 Gelation
[Z] (dl g ÿ 1)
Average Molecular weight
0.16 0.38 0.64 0.77 0.41
3.90103 1.46104 3.22104 4.24104 1.63104
C. Erbil / European Polymer Journal 35 (1999) 1747±1754
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Fig. 1. Eect of polymerization conditions on the structures of PAAm chains.
Fig. 2 and Table 2 show that the chain extension of PAAm±MA with AAm is aected by temperature and prepolymer content. The bands between 400 and 1500 cm ÿ 1 are associated with the metal±ligand and polymer±ligand complexation. The presence of these dierent complexes does not eect the polymerization yields and molecular weight but only the molecular structure of the products. As is also seen from Table 2,
Fig. 2. FTIR spectra of PAAms obtained with the chain extension of PAAm±MA prepolymer.
when the prepolymer concentration and temperature increase, the intrinsic viscosities and yields increase, as expected from the chain extension process. How-
Table 3 Block copolymerization of AN with PAAm±MA in water at 408C Prepolymer (g/50 ml)
Sample no. in Fig. 3.
Polymerization conditions
Yield (g/50 ml)
± 0.23 0.45 ± ± 0.23 0.45 0.90
1 2 3 4 5 6 7 8
Adding before AN of Ce(IV) solution Adding before AN of Ce(IV) solution Homopolymerization of AN in daylight Homopolymerization of AN in dark Adding after AN of Ce(IV) solution Adding after An of Ce(IV) solution Adding after AN of Ce(IV) solution
0.11 0.46 3.6 2.46 0.62 1.11 1.93
[Ce(IV)] = 310 ÿ 3 mol l ÿ 1; [HNO3] = 0.20 mol l ÿ 1; [AN] = 1.40 mol l ÿ 1; t = 2 h; T = 40 8C.
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ever, the dependence of the extent of reaction on temperature and prepolymer content in the polymerization mixture is opposite to the general relations of radical polymerizations, and it was assumed that this arises from the initiator composition being dierent from the others. In addition, if the temperature rises from 408 to 508C, the gel is formed. This indicates that also some of the main chain methylene groups on the prepolymer together with carboxyl end groups of the chains can generate radicals at this temperature. The eect of the order of adding reagents and daylight on the yields and block polymer formation was also investigated (Table 3 and Fig. 3). When the stock solution of the ceric salt is added to the polymerization mixture before AN (in the case of samples 2 and 3), both
yields and FTIR spectra are about the same with the prepolymer in the reaction mixture. On the other hand, in the spectra of PAN (samples 4 and 5), there is a characteristic band of the -CN group at a wavelength of 2240 cm ÿ 1 while in the spectra of samples 7 and 8, characteristic bands of both segments are observed. So, we can say that the formation rates of both homopolymer and block polymer change when the addition order of the polymerization components is changed. Although the homopolymerization of AN in aqueous medium was heterogenous, stable suspensions were obtained when the prepolymer was added into the reaction mixture. These suspensions could be precipatated in none of them while PAAm±MA and PAN were soluble in water and DMF, respectively. The suspension formation in the presence of these prepolymers may be due to:
C. Erbil / European Polymer Journal 35 (1999) 1747±1754
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Fig. 4. FTIR spectra of block copolymers prepared by various prepolymer concentrations in the dark.
Fig. 3. Eects of daylight and adding order of the reagents on
(a) Combination of prepolymer radicals to AN macroradicals produced by the propagation step of the polymerization because the obtained products are not soluble in either water or DMF. Each of these
Table 4 Block copolymerization of AN with PAAm±MA in water in the dark Prepolymer (g/50 ml)
Sample no. in Fig. 4
Polymer type
Yield (g/50 ml)
± ± 0.23 0.45 0.90
1a 2 3 4 5
Homopolymer of AN Homopolymer of AN Block copolymer + PAN Block copolymer Block copolymer
0.30 2.46 0.68 0.93 1.48
a
[AN] = 0.30 mol l ÿ 1.
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parts can be insolubility limits in the solvents of the other. The growth of PAN macroradicals and recombination with prepolymer radicals can be illustrated as follows: (PAN±PAAm block copolymers being created by recombination of PAN macroradicals with the PAAm-MA prepolymer radicals). (b) Formation of block copolymers consisting three segments (AAm±AN±AAm and AN±AAm±AN) obtained by a mutual termination process: The main dierence between the results in Table 3± Fig. 3 and Table 4±Fig. 4 is in the yields. The conversions of the polymerizations propagated in the light are higher than those obtained in the dark because of the initiated eect of the daylight on AN polymerization, whereas the FTIR spectra of the samples show about the same characteristic peaks corresponding to both PAN and PAAm±MA. In summary, our spectroscopic studies in conjection with gravimetric and viscometric results showed that, in the case of both chain extension and block copolymerization, the yield increased with prepolymer content in the reaction mixture while the homopolymer:copolymer ratio decreased in the block copolymers. As the PAAm±MA concentration in the polymerization solutions increased, the peaks relating to the metal±polymer and polymer±ligand complexes
between 400 and 1500 cm ÿ 1 increased. Furthermore, the peak at about 2240 cm ÿ 1 corresponding to the CN group of PAN was smaller than the homopolymers of AN, and the block copolymer samples obtained were yellowish-white materials, as also reported in the literature [12]. References [1] Nagarajan S, Srinivasan KSV. J Polym Sci Part A Polym Chem 1995;33:2925. [2] Wodka T. J Appl Polym Sci 1993;47:407. [3] Nagarajan S, Srinivasan KSV. Eur Polym J 1994;30 (1):113. [4] Nagarajan S, Sudhakar S, Srinivasan KSV. Colloid Polym Sci 1994;272:777. [5] C° akmak I, Hazer B, Yagci Y. Eur Polym J 1991;27(1):101. [6] Renders G, Broze R, Jerome, Teyssie Ph. J Macromol Sci Chem 1981;A16 (8):1399. [7] Bajpai UDN, Ahi A. J Appl Polym Sci 1990;40:359. [8] Hsu WC, Kuo JF, Chen CY. J Polym Sci Part A Polym Chem 1993;31:3213. [9] Sarac° AS, Erbil C, Durap F. Polym Int 1996;40:179. [10] Erbil C, UstamehmetogÆlu B, Uzelli G, Sarac° AS. Eur Polym J 1994;30 (2):149. [11] Collinson E, Dainton FS, McNaughton GS. Trans Faraday Soc 1957;53:489. [12] Soler J, Baldrian J. Angew Makromol Chem 1976;49:49.
European Polymer Journal 35 (1999) 1747±1754
Block copolymerization and chain extension by using PAAm prepolymer initiated with Ce (IV)±malonic acid Candan Erbil Istanbul Technical University, Department of Chemistry, 80626 Maslak, Istanbul, Turkey Received 9 July 1998; accepted 2 October 1998
Abstract The synthesis of block copolymers of polyacrylonitrile (PAN)±polyacrylamide (PAAm) was carried out with the use of PAAm±malonic acid (MA) prepolymer, which was a product of a redox polymerization initiated with the cerium sulphate±(MA) redox pair. The eects of prepolymer concentration and daylight on the yield and molecular structure were interpreted by means of FTIR spectroscopy. Furthermore, this prepolymer along with ceric ammonium nitrate was also used to induce the radical polymerization of acrylamide, resulting in further chain extension. Both FTIR spectra and intrinsic viscosities of the samples showed that the chain extension of PAAm±MA with AAm was aected by temperature and prepolymer content. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction The number of end groups per polymer molecule and their nature help in building block copolymers. Macromolecules containing segments with dierent chemical structures and physico-chemical properties can be obtained from synthesizing prepolymers with appropriate end groups. There are many reports in the literature on the block copolymer synthesis. Initiation by a redox process is only one method used to obtain these types of polymers [1±4]. However, initiation by a polymer having functional end groups attached to the chains, resulting from redox polymerization, has not been investigated widely in the literature [5]. Redox systems are widely used as initiators in radical polymerization. Compared to other methods, they have the prime advantage of operating at very moderate temperatures. This means that the probability of side reactions can be minimized. Ce (IV) or permanganate coupled with a hydroxyl or carboxylic group containing reductant is the initiator most often used [6±9].
Polymerization products obtained in the presence of acrylic monomers are the molecules containing the reducing substrates as end groups of the polymer chains formed. In an earlier article, we have reported the results of a study on the preparation of acrylamide (AAm) and acrylonitrile (AN) polymers having dierent numbers of carboxyl groups at the ends of chains [10]. Malonic, tartaric and citric acids were used as reducing agents in those systems. Furthermore, in that work, a conductometric titration method has been used for quantitative determination of the carboxyl end groups of polymers. This article shows the results of the investigations of block copolymerization with AN and chain extension with AAm of the polyacrylamide prepolymer initiated by the malonic acid±Ce (IV) redox pair (PAAm±MA). The aim is to ®nd the eect of prepolymer content in the reaction mixture on molecular weight (in the case of chain extension), molecular structure and yield of the synthesis.
0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 8 ) 0 0 2 8 2 - 1
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2. Experimental 2.1. Reagents Malonic acid (MA, HOOC0CH20COOH), ceric sulphate (Ce(SO4)2.4H2O), ceric ammonium nitrate ((NH4)2 Ce (NO3)6), acrylamide (AAm, CH21CH0CONH2), N, N-dimethyl formamide (DMF), sulphuric acid and nitric acid were all Merck quality and were used as supplied. Acrylonitrile (AN, CH21CH0CN) was washed successively with dilute H2SO4, Na2CO3 and water. After drying with Na2SO4, it was distilled repeatedly in N2 and stored at 58C in a refrigerator. All solutions used during the experimental work were prepared in distilled deonized water. 2.2. Experimental procedure Polymerizations were carried out in the presence of atmospheric oxygen. For the experiments, which were performed in the absence of light, the reaction vessel, as a whole, was covered with a black cloth. PAAm± MA prepolymer was prepared by redox polymerization in aqueous medium from ceric sulphate and malonic acid as described previously [10]. An appropriate solution of ceric ammonium nitrate in its respective acid was added to the aqueous solution of AAm (for chain extension) or AN (for block copolymerization) containing ®xed amounts of puri®ed PAAm±MA prepolymer. For all the polymerization experiments, a pyrex ¯ask equipped with a stirrer was
used. Both suspended copolymer, which was not precipitated from the reaction mixture during the synthesis, and PAAm obtained by chain extension of prepolymer were poured into a large excess of acetone, ®ltered o, washed with water and dried to constant weight. 2.3. Characterization Intrinsic viscosities of dilute solutions of AAm polymers in water were measured at 308C by use of an Ubbelohde suspended-level dilution viscometer. The relationship [Z] = 6.8010 ÿ 4M 0.66 was used to calculate the average molecular weights [11]. FTIR spectra were recorded using a Mattson 1000 Fourier transform IR spectrophotometer. The transmission mode was used on ®nely powdered samples prepared as KBr pellets. 3. Results and discussion From the relations between experimental conditions and FTIR spectra of the samples, the following reaction scheme is suggested for preparations of PAAm± MA prepolymer, chain extension of PAAm±MA with AAm, balances between polymer molecules and various metal complexes in the reaction media, gelation in the case of AAm polymerization at high temperatures, and block copolymerization of AN with prepolymer. The synthesis of AAm prepolymer was carried out using a redox system consisting of Ce(SO4)2.4H2O and MA.
C. Erbil / European Polymer Journal 35 (1999) 1747±1754
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the chains. The bands in the ranges of 550±650, 1100± 1200 and 1350±1450 cm ÿ 1 in the spectra of samples 2, 3 and 4 correspond to the metal±ligand complexes, and interaction of the amide groups with the complexes of Ce(IV) or Ce (III) with sulphate and nitrate or ÿ) ions such as Ce (SO4)n x(+ or ÿ) and Ce (NO3)x(+ , n respectively. The chain extension part of the polymerization mechanism can be shown by the following scheme:
The obtained prepolymer was examined by means of viscometric measurement and FTIR spectroscopy. The results of the measurements are given in Table 1 and illustrated in Fig. 1. From the comparison of the FTIR spectrum of this prepolymer with samples of PAAm initiated by K2S2O8 and (NH4)2 [Ce (NO3)6], it was observed that both Ce(IV) and anions of the salts could form complexes with the repeating units and the end groups of
Table 1 Aqueous polymerization of acrylamide initiated by various initiators at dierent temperatures Initiator
Sample no. in Fig. 1
Temperature (8C)
Product
Yield (g/50 ml)
[Z] (dl g ÿ 1)
Molecular weight
K2S2O8 MA±Ce(SO4)2.4 H2Oa (NH4)2 [Ce(NO3)6]b PAAm initiated with K2S2O8 (2.510 ÿ 3 g/50 ml) PAAm initiated with K2S2O8 (2.510 ÿ 3 g/50 ml.)
1 2 3 4
25 25 50 50
PAAm PAAm±MA prepolymer PAAm±Ce PAAm
± ± 0.67 0.30
± 0.16 0.48 0.18
02.0106 3.9103 2.1104 4.7103
±
30
±
±
±
±
a b
[MA] = 2.2210 ÿ 2 mol l ÿ 1; [Ce(IV)] = 2.2210 ÿ 2 mol l ÿ 1; [H2SO4] = 22.510 ÿ 2 mol l ÿ 1; [AAm] = 0.60 mol l ÿ 1; t = 1 h. [Ce(IV)] = 310 ÿ 3 mol l ÿ 1; [HNO3] = 0.20 mol l ÿ 1; [AAm] = 1.55 mol l ÿ 1; t = 2 h.
Table 2 Chain extension of PAAm±MA prepolymer with AAm in water Prepolymer (g/50 ml)
Sample no. in Fig. 2
Temperature (8C)
Yield (g/50 ml)
0.25 0.50 1.00 1.00 1.00
1 2 3 4 5 6
40 40 40 30 50
0.62 2.21 4.34 2.87 Gelation
[Z] (dl g ÿ 1)
Average Molecular weight
0.16 0.38 0.64 0.77 0.41
3.90103 1.46104 3.22104 4.24104 1.63104
C. Erbil / European Polymer Journal 35 (1999) 1747±1754
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Fig. 1. Eect of polymerization conditions on the structures of PAAm chains.
Fig. 2 and Table 2 show that the chain extension of PAAm±MA with AAm is aected by temperature and prepolymer content. The bands between 400 and 1500 cm ÿ 1 are associated with the metal±ligand and polymer±ligand complexation. The presence of these dierent complexes does not eect the polymerization yields and molecular weight but only the molecular structure of the products. As is also seen from Table 2,
Fig. 2. FTIR spectra of PAAms obtained with the chain extension of PAAm±MA prepolymer.
when the prepolymer concentration and temperature increase, the intrinsic viscosities and yields increase, as expected from the chain extension process. How-
Table 3 Block copolymerization of AN with PAAm±MA in water at 408C Prepolymer (g/50 ml)
Sample no. in Fig. 3.
Polymerization conditions
Yield (g/50 ml)
± 0.23 0.45 ± ± 0.23 0.45 0.90
1 2 3 4 5 6 7 8
Adding before AN of Ce(IV) solution Adding before AN of Ce(IV) solution Homopolymerization of AN in daylight Homopolymerization of AN in dark Adding after AN of Ce(IV) solution Adding after An of Ce(IV) solution Adding after AN of Ce(IV) solution
0.11 0.46 3.6 2.46 0.62 1.11 1.93
[Ce(IV)] = 310 ÿ 3 mol l ÿ 1; [HNO3] = 0.20 mol l ÿ 1; [AN] = 1.40 mol l ÿ 1; t = 2 h; T = 40 8C.
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ever, the dependence of the extent of reaction on temperature and prepolymer content in the polymerization mixture is opposite to the general relations of radical polymerizations, and it was assumed that this arises from the initiator composition being dierent from the others. In addition, if the temperature rises from 408 to 508C, the gel is formed. This indicates that also some of the main chain methylene groups on the prepolymer together with carboxyl end groups of the chains can generate radicals at this temperature. The eect of the order of adding reagents and daylight on the yields and block polymer formation was also investigated (Table 3 and Fig. 3). When the stock solution of the ceric salt is added to the polymerization mixture before AN (in the case of samples 2 and 3), both
yields and FTIR spectra are about the same with the prepolymer in the reaction mixture. On the other hand, in the spectra of PAN (samples 4 and 5), there is a characteristic band of the -CN group at a wavelength of 2240 cm ÿ 1 while in the spectra of samples 7 and 8, characteristic bands of both segments are observed. So, we can say that the formation rates of both homopolymer and block polymer change when the addition order of the polymerization components is changed. Although the homopolymerization of AN in aqueous medium was heterogenous, stable suspensions were obtained when the prepolymer was added into the reaction mixture. These suspensions could be precipatated in none of them while PAAm±MA and PAN were soluble in water and DMF, respectively. The suspension formation in the presence of these prepolymers may be due to:
C. Erbil / European Polymer Journal 35 (1999) 1747±1754
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Fig. 4. FTIR spectra of block copolymers prepared by various prepolymer concentrations in the dark.
Fig. 3. Eects of daylight and adding order of the reagents on
(a) Combination of prepolymer radicals to AN macroradicals produced by the propagation step of the polymerization because the obtained products are not soluble in either water or DMF. Each of these
Table 4 Block copolymerization of AN with PAAm±MA in water in the dark Prepolymer (g/50 ml)
Sample no. in Fig. 4
Polymer type
Yield (g/50 ml)
± ± 0.23 0.45 0.90
1a 2 3 4 5
Homopolymer of AN Homopolymer of AN Block copolymer + PAN Block copolymer Block copolymer
0.30 2.46 0.68 0.93 1.48
a
[AN] = 0.30 mol l ÿ 1.
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parts can be insolubility limits in the solvents of the other. The growth of PAN macroradicals and recombination with prepolymer radicals can be illustrated as follows: (PAN±PAAm block copolymers being created by recombination of PAN macroradicals with the PAAm-MA prepolymer radicals). (b) Formation of block copolymers consisting three segments (AAm±AN±AAm and AN±AAm±AN) obtained by a mutual termination process: The main dierence between the results in Table 3± Fig. 3 and Table 4±Fig. 4 is in the yields. The conversions of the polymerizations propagated in the light are higher than those obtained in the dark because of the initiated eect of the daylight on AN polymerization, whereas the FTIR spectra of the samples show about the same characteristic peaks corresponding to both PAN and PAAm±MA. In summary, our spectroscopic studies in conjection with gravimetric and viscometric results showed that, in the case of both chain extension and block copolymerization, the yield increased with prepolymer content in the reaction mixture while the homopolymer:copolymer ratio decreased in the block copolymers. As the PAAm±MA concentration in the polymerization solutions increased, the peaks relating to the metal±polymer and polymer±ligand complexes
between 400 and 1500 cm ÿ 1 increased. Furthermore, the peak at about 2240 cm ÿ 1 corresponding to the CN group of PAN was smaller than the homopolymers of AN, and the block copolymer samples obtained were yellowish-white materials, as also reported in the literature [12]. References [1] Nagarajan S, Srinivasan KSV. J Polym Sci Part A Polym Chem 1995;33:2925. [2] Wodka T. J Appl Polym Sci 1993;47:407. [3] Nagarajan S, Srinivasan KSV. Eur Polym J 1994;30 (1):113. [4] Nagarajan S, Sudhakar S, Srinivasan KSV. Colloid Polym Sci 1994;272:777. [5] C° akmak I, Hazer B, Yagci Y. Eur Polym J 1991;27(1):101. [6] Renders G, Broze R, Jerome, Teyssie Ph. J Macromol Sci Chem 1981;A16 (8):1399. [7] Bajpai UDN, Ahi A. J Appl Polym Sci 1990;40:359. [8] Hsu WC, Kuo JF, Chen CY. J Polym Sci Part A Polym Chem 1993;31:3213. [9] Sarac° AS, Erbil C, Durap F. Polym Int 1996;40:179. [10] Erbil C, UstamehmetogÆlu B, Uzelli G, Sarac° AS. Eur Polym J 1994;30 (2):149. [11] Collinson E, Dainton FS, McNaughton GS. Trans Faraday Soc 1957;53:489. [12] Soler J, Baldrian J. Angew Makromol Chem 1976;49:49.