Radical polymerization of methacrylates having acetylenic moiety activated by electron-withdrawing group as a reactive functional group

REACTIVE & FUNCTIONAL POLYMERS Reactive & Functional Polymers 66 (2006) 229–238 www.elsevier.com/locate/react Radical polymerization of methacrylates having acetylenic moiety activated by electron-withdrawing group as a reactive functional group Hirofumi Kuroda *, Sayaka Nakatsuchi, Nobuyoshi Kitao, Tsuyoshi Nakagawa Department of Chemical and Biochemical Engineering, Toyama National College of Technology, 13 Hongo-machi, Toyama-shi, Toyama 939-8630, Japan Received 18 March 2005; received in revised form 1 July 2005; accepted 11 July 2005 Available online 21 September 2005 Abstract The synthesis of methacrylates having an acetylene moiety activated by an electron-withdrawing group and a radical polymerization of the methacrylates are described. The methacrylates were prepared from alkynoic acids via x-hydroxyalkyl alkynoates in two steps. This was done by the radical polymerization of the synthesized methacrylates, polymthacrylates having the acetylene moieties activated by the electron-withdrawing group as the side-chain that were obtained in high yields. In the radical polymerization, the acetylene moiety slightly hindered the polymerization of the methacrylate moiety. The influences of the acetylene moiety decreased with the introduction of substituents at the acetylene moiety. The polymer reaction of the obtained polymer having the acetylenic side chain with thiols gave the corresponding polymers having the b-alkylmercaptoenoate moiety in high yields. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Radical polymerization; Methacrylates; Acetylenes; Electron-withdrawing groups; Reactive polymer 1. Introduction Functionalized polymers are frequently synthesized by the polymer reactions of polymers having reactive functional groups [1]. In this method, the reactivity of the functional groups is one of the * Corresponding author. Tel./fax: +81 76 493 5464. E-mail address: kuroda@toyama-nct.ac.jp (H. Kuroda). important factors because the reactivity of the functional groups in the polymer is generally lower than the reactivity of the functional groups in the monomer by the steric affect and the interaction of the functional groups in the polymer. Consequently, more reactive functional groups, more active reagents, harder conditions, and so on are required in the reactions of polymers compared with those of low molecular weight compounds. 1381-5148/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2005.07.027 230 H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 Acetylenes activated by electron-withdrawing groups are one of the relatively highly reactive compounds, and it is known the anionic reactivity of the acetylenic compounds is higher than that of the corresponding olefins [2]. In organic synthesis, such acetylenes are the one of most important substrates and widely used as a key intermediate [3]. Therefore, acetylene moieties activated by the electron-withdrawing group are also one of the interesting reactive functional groups in the polymer synthesis. We have reported upon polymer synthesis using the high anionic reactivity of acetylene activated by electron-withdrawing as a functional group for polymerization [4]. For example, the polyaddition of bifunctional acetylenes activated by an electron-withdrawing group with diols proceeded smoothly under the mild conditions observed in the presence of trialkylphosphine as a mild catalyst to give polymers having C–C double bonds in the main chain in high to almost quantitative yields [4a,4b]. Thus, an acetylenic skeleton activated by the electron-withdrawing group might also be one of the attractive functional groups in polymer reactions. Generally, radical additions to C–C triple bonds are much less common than such additions to C–C double bonds [5]. In fact, it is much more difficult to obtain polyacetylenes effectively by the radical polymerization of acetyelenes [6]. Therefore, in a molecular design of the monomers having acetylene moieties activated by the electron-withdrawing group as a reactive functional group, the selection of methacrylates as radically polymerizable monomers may be preferable to the chemical properties of acetylenes. Thus, we have designed methacrylates (1) having acetylene moieties activated by the electron-withdrawing group as a novel reactive monomer. Both the property of the polymer obtained from 1, and the radical polymerization behavior of 1 are interesting. Herein, we wish to describe the synthesis and radical polymerization of 1 (Scheme 1). 2. Experimental Materials and instruments. Tetrahydrofuran (THF) was dried over sodium benzophenone ketyl and distilled under nitrogen. Dichloromethane and dimethylformamide (DMF) were dried over calcium hydride and then purified by distillation. Methyl methacrylate (MMA) was distilled under vacuum. Other commercially available chemicals were used without purification. Methyl 2-heptynoate was prepared from methyl chloroformate and 1-hexyne in 78% yield according to the method described in the literature [6]. The infrared (IR) spectra were obtained with a JASCO FT/IR 8000 infrared spectrometer. The 1 H- and 13C NMR spectra were recorded on JNM-FX90 or AL400 spectrometers, in CDCl3 (using tetramethylsilane as an internal standard). Gel permeation chromatographic analysis (GPC) was performed on a GPC system equipped with SHODEX KF-804L and KF-80M (PSt, THF as an eluent). 2.1. 2-Heptynoic acid (3b) 3b was prepared by the modification of the method described in the literature [7]. n-Butyllithium (1.56 M in hexane, 63.0 mL, 98.3 mmol) was added dropwise to a solution of 1-hexyne (5.00 g, 61.0 mmol) in diethyl ether (40 mL) at À80 °C under nitrogen and the mixture was then stirred for 30 min at this temperature. Carbon dioxide was gently introduced into the mixture, which was kept at a temperature of between 0 CH 3 Radical Polymerization CO2CH2CH2 O2C R n H3C CO2CH2CH2O2C 2a: R=H 2b: R=Bu 1a: R=H 1b: R=Bu Scheme 1. R H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 and À10 °C. After the exothermic reaction had ceased, the resulting solution was cautiously poured into 200 mL of ice water. The organic layer was separated and then extracted twice with 40 mL of water. To the combined aqueous layer was added concentrated hydrochloric acid in small portions with cooling in an ice bath until a pH of one had been reached. The mixture was extracted five times with 40 mL of diethyl ether. The extracts were dried over magnesium sulfate and then the drying agent was filtered off. After the evaporation of the solvents, the residue was purified by vacuum distillation to give 3b (10.3 g, 81.8 mmol, 81%: colorless oil, bp2 76–79 °C); IR (neat) 2961, 2242, 1699, 1281 cmÀ1; 1H NMR (90 MHz, d, ppm) 0.89 (t, J = 7.4 Hz, 3H, CH3CH2–), 1.36–1.58 (m, 4H, –CH2–), 2.33 (t, J = 7.2 Hz, 2H, CH2C„C–), 11.24 (bs, 1H, –CO2H). 2.2. 2-Hydroxyethyl 2-propynoate (4a) To a solution of 2-propynoic acid (3.50 g, 50.0 mmol) and ethylene glycol (46.8 mL, 755 mmol) was added p-toluenesulfonic acid monohydrate (1.63 g, 8.64 mmol). The mixture was stirred at 60 °C for 24 h and then poured into 100 mL of saturated aqueous sodium bicarbonate. The organic layer was extracted four times with 30 mL of ethyl acetate. The combined organic layers were dried over magnesium sulfate. After the evaporation of the solvents, the residue was purified by vacuum distillation to give 3.87 g (33.9 mmol, 67.9%) of 4a (bp1.0 63–64 °C, colorless oil); IR (neat) 3400, 3266, 2962, 2120, 1715, 1455, 1372, 1246 cmÀ1; 1H NMR (90 MHz, d, ppm) 2.88 (bs, 1H, –OH), 2.98 (s, 1H, HC„C), 3.80 (t, J = 4.8 Hz, 2 H, CH2OH), 4.22 (t, J = 4.8 Hz, 2H, –CO2CH2–). 231 –CH2C„C), 2.37 (bs, 1H, –OH), 3.68 (t, J = 5.4 Hz, 2H, –CH2OH), 4.22 (t, J = 5.4 Hz, 2H, –CO2CH2–). 2.4. Ethylene methacrylate propynoate (1a) To a solution of 4a (2.50 g, 21.9 mmol) and methacrylic anhydride (4.05 g, 26.3 mmol) in CH2Cl2 were added p-toluenesulfonic acid monohydrate (0.418 g, 2.19 mmol) and 4-t-butylcatecol (0.010 g, 0.06 mmol). The mixture was refluxed for 12 h and then poured into 10 mL of saturated aqueous sodium bicarbonate. After extraction with 10 mL of ethyl acetate three times, the combined organic layers were concentrated in a vacuum. The residue was treated with 0.1 M sodium hydroxide (50 mL) for 15 min and then the mixture was extracted three times with 20 mL of ethyl acetate. The combined organic layers were washed with 20 mL of saturated aqueous ammonium chloride, dried over magnesium sulfate and then the drying agent was filtered off. After evaporation of the solvents, the residue was purified by column chromatography on silica gel (ethyl acetate/hexane = 200:1–50:1) to obtain 2.22 g (12.2 mmol, 55.7%) of 1a (Rf = 0.28, ethyl acetate/hexane = 1/4, colorless oil); IR (neat) 3258, 2963, 2122, 1719, 1638, 1455, 1229, 1165 cmÀ1. 1H NMR (400 MHz, d, ppm) 1.88 (s, 3H, CH3–), 2.90 (s, 1H, HC„C), 4.31 (m, 2H, CO2CH2–), 4.39 (t, J = 5.2 Hz, 2H, –CO2CH2–), 5.54 (s, 1H, CH2@), 6.07 (s, 1H, CH2@). 13C NMR (100 MHz, d, ppm) 18.3 (CH3–), 61.9 (–CO2CH2–), 63.6 (–CO2CH2–), 74.2 (HC„C–), 75.5 (HC„C), 126.1 (CH2@), 135.5 (CH2@C—), 152.1 (HC„CCO2–), 166.7 (@CMeCO2–). 13C NMR (22.5 MHz, d, ppm) 18.2 (CH3–), 61.9 (–CO2CH2–), 63.7 (CO2CH2–), 74.4 (HC„C–), 75.4 (HC„), 126.2 (CH2@), 135.8 (CH2@C—), 152.3 (HC„CCO2–), 167.0 (@CMeCO2–). 2.3. 2-Hydroxyethyl 2-heptynoate (4b) 2.5. Ethylene 2-hexynoate methacrylate (1b) Similarly, 4b (bp0.01 91–93 °C, colorless oil) was synthesized from 3b and ethylene glycol in 93.6% yield. IR (neat) 3378, 2926, 2245, 1725, 1456, 1371, 1269 cmÀ1; 1H NMR (90 MHz, d, ppm) 0.86 (t, J = 7.4 Hz, 3H, CH3–), 1.32–1.54 (m, 4H, –CH2CH2CH3), 2.28 (t, J = 7.4 Hz, 2H, Similarly, 1b (Rf = 0.45, ethyl acetate/hexane = 1/4, colorless oil) was prepared from 4b and methacrylic anhydride in 81.7% yield. IR (neat) 2961, 2874, 2235, 1718, 1637, 1454, 1371, 1321, 1298, 1250, 1165 cmÀ1. 1H NMR (400 MHz, d, 232 H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 ppm) 0.89 (t, J = 7.2 Hz, 3H, CH3–), 1.40 (m, 2H, CH3CH2–), 1.53 (m, 2H, –CH2CH2–), 1.92 (s, 3H, CH3–), 2.31 (J = 7.0 Hz, 2H, –CH2C„), 4.31 (m, 2H, –CO2CH2–), 4.39 (m, 2H, –CO2CH2–), 5.56 (s, 1H, CH2@), 6.10 (s, 1H, CH2@). 13C NMR (100 MHz, d, ppm) 13.4 (–CH2C„), 18.2 (CH3–), 18.4 (CH3–), 22.0 (–CH2–), 29.5 (–CH2–), 62.1 (–CO2CH2–), 63.2 (–CO2CH2–), 72.8 (–CH2C„C–), 90.6 (–CH2C„), 126.1 (CH2@), 135.9 (CH2@C—), 153.5 (–C„CCO2–), 167.1 (@CMeCO2–). 2.6. Radical polymerization of 1 Typical procedure. The polymerization of 1a was carried out as follows: To a solution of 1a (0.500 g, 2.74 mmol) in DMF (5.0 mL) in a glass tube was added 2,2 0 -azobis(isobutyronitrile) (AIBN) (0.013 g 0.082 mmol). The tube was cooled, degassed, sealed off, and heated at 60 °C for 15 h. The reaction mixture was poured into methanol (100 mL). The precipitate was filtered and dried under vacuum to obtain 2a (0.458 g, 91.6%). IR (neat) 3252, 2959, 2120, 1725, 1451, 1229, 1152 cmÀ1. 1H NMR (400 MHz, d, ppm) 0.7–1.4 (3H, CH3–), 1.7–2.1 (2H, CH2CMe—), 2.6–3.5 (1H, HC„), 4.13 (m, 2H, –CO2CH2–), 4.30 (m, 2H, CO2CH2–). Similarly, 2b was prepared by the radical polymerization of 1b. 2b: IR (neat) 2959, 2236, 1717, 1455, 1256, 1150, 1078 cmÀ1. 1H NMR (400 MHz, d, ppm) 0.9 (t, J = 7.1 Hz, 3H, CH3CH2–), 0.7–1.1 (3H,CH3–), 1.40 (m, 2H, –CH2–), 1.55 (m, 2H, –CH2–), 1.7–2.1 (2H, –CH2CMe—), 2.32 (t, J = 6,1 Hz, 2H, –CH2C„), 3.9–4.6 (4H, –CO2CH2CH2–). 2.7. Radical polymerization of MMA in the presence of acetylenic compounds Typical procedure. The polymerization of MMA in the presence of methyl propiolate was carried out as follows: To a solution of MMA (0.102 g, 1.02 mmol) in DMF (1.8 mL) in a glass tube were added AIBN (0.005 g, 0.0306 mmol) and methyl propiolate (0.0857 g, 1.02 mmol). The tube was cooled, degassed, sealed off, and heated at 60 °C for 15 h. The reaction mixture was poured into methanol (100 mL). A precipitate was not obtained. Similarly, the radical polymerizations of MMA in the absence of acetylenic compounds and in the presence of methyl 2-hexynoate were also carried out to obtain poly(methyl methacrylate) (PMMA) in 43% and 22% yields, respectively. 2.8. Radical copolymerization of 1b with vinyl monomers The copolymerization of 1b with MMA was carried out as follows: To a solution of 1b (0.127 g, 0.532 mmol) and MMA (0.117 g, 1.17 mmol) in DMF (3 mL) in a glass tube was added AIBN (0.008 g 0.0487 mmol). The tube was cooled, degassed, sealed off, and heated to 60 °C for 24 h. The reaction mixture was poured into methanol (60 mL). The precipitate was filtered and dried under vacuum to obtain the corresponding copolymer (0.197 g, 80.8%). IR (neat) 2959, 2237, 1718, 1450, 1257, 1149 cmÀ1. 1H NMR (90 MHz, d, ppm) 0.95 (CH3–), 0.71–2.20 (–CH2CH2CH3, –CH2C(CH3)CO–), 2.18 (–CH2C„), 3.58 (CO2CH3), 4.00–4.60 (–CO2CH2–). From the integral ratio in the 1H NMR spectrum, the unit ratio of the copolymer was estimated to be ca. 1:2 [poly(1b):PMMA]. Similarly, the copolymerization of 1b (0.115 g, 0.485 mmol) with styrene (0.109 g, 1.05 mmol) was also carried out to obtain the corresponding copolymer in 53% yield. IR (neat) 2934, 2237, 1717, 1454, 1253, 702 cmÀ1. 1H NMR (90 MHz, d, ppm) 0.92 (CH3–), 0.51–2.12 (–CH2CHPh–, –CH2CH2CH3, –CH2C(CH3)CO–), 2.20–2.57 (CH2C„, CH2CHPh–), 3.48–4.53 (–CO2CH2–), 6.18–7.51, Ph). From the integral ratio in the 1H NMR spectrum, the unit ratio of the copolymer was estimated to be ca. 1:2 [poly(1b):PSt]. 2.9. Phosphine-catalyzed polymer reaction of 2 with thiols The reaction of 2a with benzylmercaptane was carried out to obtain 5aA as follows: To a solution of polymer (2a) (0.100 g, 0.549 mmol of unit) in THF (0.6 mL) and benzylmercaptane (0.075 g, 0.604 mmol) was added tributylphosphine (0.022 g, 0.110 mmol) under nitrogen at room temperature. The reaction mixture was poured into H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 hexane (20 mL). The precipitate was filtered and dried under vacuum to obtain 5aA (0.157 g, 93.4%). IR (neat) 2957, 1732, 1574, 1454, 1232, 1161 cmÀ1. 1H NMR (400 MHz, d, ppm) 0.7–1.0 (3H, CH3), 1.7–2.1 (2H, CH2CMe—), 3.8–4.3 (6H, PhCH2S– and –OCH2CH2O–), 5.6–5.8 (1H, SCH@CH–), 7.2 (5H, Ph), 7.6–7.7 (1H, –SCH@CH–). Similarly, the reactions of 2b with benzylmercaptane or thiophenol were carried out to obtain 5bA or 5bB, respectively. 5bA: Yield 80.2%, IR (neat) 2959, 1715, 1590, 1455, 1248, 1169 cmÀ1. 1H NMR (400 MHz, d, ppm) 0.7–1.1 (6H, CH3CH2– and –CH2CMe—), 1.1–2.0 (6H, CH2CMe—, and CH3CH2CH2–), 2.70 (2H, –CH2C„C–), 3.8–4.3 (6H, PhCH2S– and –OCH2CH2O–), 5.5 (1H, S(Bu)C@CH–), 7.1–7.3 (5H, Ph). 5bB: Yield 83.1%, IR (neat) 2959, 1732, 1705, 1580, 1441, 1441, 1171 cmÀ1. 1H NMR (400 MHz, d, ppm) 0.5–1.1 (6H, CH3CH2– and –CH2CMe—), 1.5–2.0 (6H, CH2CMe—, and CH3CH2CH2–), 2.30 (2H, Z-CH2C„C–), 2.8 (2H, E-CH2C„C–), 3.8–4.3 (4H, –OCH2CH2O–), 5.2 (1H, E-S(Bu)C@CH–), 5.8 (1H, Z-S(Bu)C@ U:/ES/DTD501/React/1994CH–), 7.1–7.3 (5H, Ph) (E:Z = 1:2). OH HO R 233 R CO2H CO2 3 OH 4 CH3 O CO 2 CH 3 CO2CH2CH2 O2C PTSA R 1a: R=H 1b: R=Bu Scheme 2. onic acid (PTSA) was carried out to yield 4 in 68– 94% yield. For the preparation of 1, the esterification of 4 with methacrylic acid in the presence of trifluoroacetic anhydride [8] as an activator of carboxylic acid was tried as a reaction under acidic and mild conditions. However, pure 1 was not obtained due to contamination by trifluoroacetate because the removal of the by-product was very difficult. As another method of preparation, we tried the esterification of 4 using methacrylic anhydride in the presence of PTSA as a catalyst with slight heating. In this method, we were able to obtain pure 1 in 56–82% yields. 3.2. Radical polymerization of 1 3. Results and discussion 3.1. Synthesis of methacrylates (1) having the acetylene moiety activated by the electronwithdrawing group Methacrylates (1) having the acetylene moiety activated by the electron-withdrawing group were synthesized from 2-alkanoic acids (3) via xhydroxyalkyl alkynoate (4) in two steps (Scheme 2). Acetylenic compounds activated by the electron-withdrawing group are generally labile under basic conditions, and a conjugate addition [4a,4c] of alcohols to such acetylenes takes place easily under those conditions because of the high anionic reactivity. So we attempted the preparation of methacrylates (1) under acidic conditions. The esterification of alkanoic acid with excess amounts of ethylene glycol in the presence of p-toluenesulf- The radical polymerization of 1 was examined at 60 °C in DMF in the presence of AIBN at various concentrations to obtain 2 (Table 1). When the polymerization of 1a and 1b was carried out without solvents, the obtained polymers were insoluble in common organic solvents such as THF, DMF, CHCl3 and so on (Runs 1 and 5). In the IR spectra of these insoluble polymers, the absorption due to the C–C triple bond was clearly observed. Furthermore, the polymerization was performed with DMF as a solvent under various concentrations. Although the soluble polymer was not obtained at high monomer concentrations in the polymerization of 1a (Runs 1 and 2), the soluble polymer (2a) was obtained in high yield by performing the polymerization at 0.5 M of the monomer concentration (Run 3). The numberaverage molecular weight (Mn) and the molecular distribution (Mw/Mn) were estimated to be 8,100 234 H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 Table 1 Radical polymerization of 1 at various concentrationsa Run R Solvent/M Yieldb (%) Mn (Mw/Mn)d 1 2 3 4 5 6 7 8 9 10 H (1a) Bulk DMF/1.0 DMF/0.5 DMF/0.2 Bulk DMF/2.0 DMF/1.0 DMF/0.7 DMF/0.5 DMF/0.2 89c 88c 86 7 88c 92 91 88 87 66 –e –e 8100 (2.03) 5500 (1.40) –e 60,400 (6.68) 46,600 (2.00) 24,400 (1.92) 20,700 (1.92) 13,800 (1.56) a b c d e n-Bu(1b) The polymerization of 1 was examined at 60 °C in DMF in the presence of AIBN (3 mol%) at various concentrations. Isolated yield after precipitation with methanol. The obtained polymer was insoluble in common organic solvents (DMF, THF, CH2Cl2, etc.). Estimated by GPC (PSt, THF as an eluent). Not estimated. and 2.03, respectively, from the GPC analysis. The structures of the obtained polymers were confirmed by 1H NMR and IR analysis. Both of the spectra of 2a are shown in Figs. 1 and 2. In the IR spectrum of 2a, the absorptions were observed at about 3250 (an attributable absorption to H– C„) and 2120 (an attributable absorption to C„C) cmÀ1 similarly to 1a. In the 1H NMR spectrum of 2a, the signals of the olefinic protons assigned to the methacrylate moiety of 1a disappeared and a signal of the acetylenic proton was observed at 2.6–3.5 ppm in a similar way to 1a. The C–C triple bond in the obtained polymer was detected quantitatively from the integral ratio Fig. 2. 1H NMR spectra (90 MHz, CDCl3) of 1a (a) and 2a (b). Fig. 1. IR spectra of 1a (a) and 2a (b). between this peak and the peaks of other protons. An almost quantitative existence of the acetylene moiety was verified in both spectra. The yield of the polymer decreased at lower monomer concentrations (0.2 M, Run 4). In the polymerization of 1b in DMF (2.0–0.2 M), the soluble polymer was also obtained. The molecular distribution of 2b obtained at 2.0 M was broad compared with those of 2b obtained at lower monomer concentrations (Runs 6–10). Gelation might take place depending on the monomer concentrations because of the addition of radical species to the acetylene moiety slightly proceeding at high monomer concentrations (Scheme 3) [9]. The effects of the monomer concentration was H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 R 235 CO2 CH3 C• CO2 CH3 R C CO2 O 2C • R CH3 R CO2 O 2C C CO2 R CO2 O 2C R Scheme 3. prominent in the case of 1a compared with 1b. The tendency might be due to a difference between the reactivity of the two acetylene moieties: the terminal acetylenes are more reactive compared with internal acetylenes. It was found from the results that the polymerization at appropriate monomer concentrations has to be carried out in order to obtain soluble polymers having the acetylene moieties as a side chain in higher yield. The radical polymerization of methyl methacrylate (MMA) was carried out in the presence (1 equiv.) of methyl propiolate or methyl 2-heptynoate in order to investigate the influence of the acetylenic skeleton toward the radical polymerization of the methacrylate moiety (Table 2). When the radical polymerization of MMA was carried out in DMF (0.5 M) at 60 °C, poly(methyl methacrylate) (PMMA) (Mn = 23,600, Mw/Mn = 1.42) was obtained in 44% yield (run 1). However, PMMA was not obtained in the presence of methyl propi- Table 2 Radical polymerization of MMA in the presence of acetylenic compoundsa R 1 2 3 Yieldb (%) R Run None H n-Bu Mn (Mw/Mn)c 43 0 22 23,600 (1.42) – 26,400 (1.22) CO2Me a The polymerization of methyl methacrylate (MMA) was carried out in the presence (1 equiv.) of acetylenic compounds by using AIBN (3 mol %) in DMF (0.5 M) at 60 °C. b Isolated yield after precipitation with methanol. c Estimated by GPC (PSt, THF as an eluent). olate (run 2). Furthermore, in the presence of methyl 2-heptynoate, the yield of PMMA decreased by about half compared with in the absence of acetylenic compounds (run 3). The presence of acetylenic compounds hindered the radical polymerization of methacrylate and the tendency was particularly noticeable in the case of terminal acetylene. Such an inhibition of polymerization by acetylenes has also been reported by Doak [5c]. In the paper, it has been described that the addition of a small amount of phenylacetylene reduced the overall rate of polymerization, accompanied by a decrease in a molecular weight of the polymer because of the formation of a vinyl radical derived from phenylacetylene formed radicals, which do not readily propagate the chain. Therefore, the acetylene moiety in 1 might inhibit the polymerization of the methacrylate moiety at lower monomer concentrations by the formation of a vinyl radical whose propagation ability is relatively low. The polymerization of MMA in the presence of acetylenic compounds (1 equiv.) was also carried out without solvent at 60 °C for 24 h and the components of the reaction mixture were estimated by 1 H NMR spectroscopy (400 MHz). In the case of coplymerization with methyl propiolate, the conversions of MMA and methyl propiolate were estimated to be ca. 84% and ca. 34% [10], respectively. Similarly, the conversions of MMA and methyl 2heptynoate were estimated to be 99% and 19%, respectively, when methyl 2-heptynoate was employed as the comonomer. From these results, it was found that the influence of methyl 2-heptyno- 236 H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 Table 3 Radical polymerization of 1 at various temperatures Run R Initiatorsa Temp (°C) Yieldb (%) Mn (Mw/Mn)c 1d 2d 3d 4f 5f 6f 7f 8f 9f H (1a) AIBN BPO DTBP AIBN BPO DTBP AIBN BPO DTBP 60 80 120 60 80 120 60 80 120 86 91 17 99 100 74 89 98 82 8100 (2.03) 13,600 (2.78) 16,100 (2.34) –e –e 5500 (1.97) 38,600 (2.25) –e 38,600 (3.68) a b c d e f n-Bu (1b) AIBN, 2,2 0 -azobis(isobutytronitrile); BPO, benzoyl peroxide; DTBP, Di-t-butyl peroxide. Isolate yield after precipitation with methanol. Estimated by GPC (PSt, THF as an eluent). The polymerization was carried out in DMF (0.5 M). The obtained polymer was insoluble in common organic solvent (DMF, THF, CH2Cl2, etc.). The polymerization was carried out in DMF (1.0 M). ate toward radical polymerization is slight compared with methyl propiolate. The gelation in high monomer concentrations might be due to the addition of radical species to the acetylene moiety because the consumption of acetylenes in the polymerization of MMA in the presence of acetylenes without solvents was confirmed. The polymerization of 1 was also tried at various temperatures. The results are shown in Table 3. When the polymerization of 1a was carried out in DMF (0.5 M) at various temperatures, 2a having the higher molecular weight and broader molecular weight distribution was obtained in higher yield at 80 °C compared with the case at 60 °C (Runs 1 and 2). In contrast, the yield of 2a decreased significantly at 120 °C (Run 3). Furthermore, the polymerization of 1a was examined at a higher monomer concentration (1.0 M) and various temperatures (Runs 4–6). The soluble 2a was obtained in high yield at 120 °C although the gela- tion took place at both 60 and 80 °C (Runs 4 and 5). The polymerization of MMA was carried out at various temperatures in order to investigate the variation of the polymerizablility of the methacrylate moiety in 1a (Table 4). As shown in Table 4, the molecular weights of the obtained PMMA increased with rising polymerization temperature. From these results, the difference in the polymerization behavior in Table 3 (Runs 1–6) may be due to the propagation ability of the vinyl radical derived from the acetylene moiety of 1a, as shown in Scheme 3, changing in response to varying temperatures. The radical polymerizabilty of the acetylene moiety might increase due to the moderate rise in the polymerization temperature and the decrease at higher polymerization temperatures. Therefore, in the case of Run 6 in Table 3, the soluble 2a might be obtained in spite of a high monomer concentration. In the case of Run 3 in Table 3, the yield of 2a might decrease due to that acetylene Table 4 Radical polymerization of MMA at various temperaturesa Run Initiators Temp (°C) Yieldb (%) Mn (Mw/Mn)c 1 2 3 AIBN BPO DTBP 60 80 120 60 74 69 57,000 (1.42) 63,000 (1.59) 78,000 (1.76) a b c The polymerization was carried out in the presence of various initiators (3 mol%) in DMF (1.0 M). Isolate yield after precipitation with methanol. Estimated by GPC (PSt, THF as an eluent). H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 237 CH3 CH 3 CO2CH2CH2 O2C + Bu CO2 Me 1b AIBN, DMF n m CO2Me H 3C CO2CH2CH2 O2 C 60 ˚C, 24 h Bu CH 3 CO2CH2CH2 O2C + Bu Ph 1b AIBN, DMF m 60 ˚C, 24 h Ph n H 3C CO2CH2CH2 O2 C Bu Scheme 4. moiety preventing the desired polymerization in the low monomer concentration. This tendency on the variation of the polymerization temperature was also observed in the case of 1b (Runs 7–9 in Table 3). The copolymerization of 1b with common vinyl monomers (2 equiv.) such as styrene and MMA was carried out in the presence of AIBN in DMF (monomers concentration; 0.5 M) at 60 °C (Scheme 4). When MMA was used as the comonomer, the copolymer having Mn = 17,300 and Mw/ Mn = 2.19 was obtained in 81% yield as an insoluble part in methanol. In the case of styrene, the copolymer having (Mn = 9200, Mw/Mn = 1.54) was also obtained in 53% yield. The unit ratios of the obtained copolymers reflected the monomer feed ratio. 3.3. Polymer reaction of 2 The anionic reactivity of acetylenes activated by the electron-withdrawing group is high, as described above. The polymer reaction of 2a and 2b with thiols in the presence of tributylphosphine as a catalyst was tried (Scheme 5). The reaction was carried out in THF under nitrogen at room temperature. When benzylmercaptane or thiophenol were used as the thiols, the corresponding polymers (5) having a b-alkylmercaptoenoate moiety as a side chain were obtained in high yield. The polymers were soluble in common organic solvents such as THF, DMF, and CHCl3. It was suggested that the acetylene moiety in 2 was converted quantitatively to a b-alkylmercaptoenoate moiety in all cases because the strong absorption of the C–C triple bond conjugated with a carbonyl group in the IR spectroscopy disappeared in the reaction and the integral value of the phenyl group, and the newly formed double in the 1H NMR spectroscopy almost agreed with the theoretical values. When 2a (Mn = 8000, Mw/Mn = 1.73) and 2b (Mn = 38,600, Mw/Mn = 3.62) were employed as the starting polymer, the polymers whose molecular weights and molecular distributions were 5800 and 1.33 (5aA), 25,400 and 3.04 (5bA), and 13,300 and 1.99 (5bB), respectively, were obtained. In the R'SH n H3C CO2CH2CH2O2C R Bu 3P cat. n H3C CO2CH2CH2O2C SR' R 2 5aA: R=H, R'=Bn 5bA: R=Bu, R'=Bn 5bB: R=Bu, R'=Ph Scheme 5. 238 H. Kuroda et al. / Reactive & Functional Polymers 66 (2006) 229–238 GPC measurement, all of the obtained polymers showed lower molecular weights than the starting polymers. Although it is known that the transesterification in the anionic reaction of alkynoates with alcohols take place as a side reaction [4a], such a side reaction is not observed in the phosphine catalyzed reaction of the alkynoates with thiols, and the corresponding adducts are obtained in almost quantitative yields [4b]. Furthermore, it is difficult to believe that the fission of some of the covalent bonds occurred by the phosphine-catalyzed reaction from the reaction mechanism [4,11]. Based on this, the decrease in the molecular weight by the polymer reaction may not be due to some of the side reactions. We think the degree of polymerization may not change [12]. 4. Conclusion The synthesis of methacrylates (1) having an acetylene moiety activated by the electron-withdrawing group and radical polymerization of 1 were described. Methacrylates (1) were prepared from alkynoic acids via x-hydroxyalkyl alkynoates in two steps. By the radical polymerization of 1, polymthacrylates (2) having an acetylene moiety activated by the electron-withdrawing group as the side-chain were obtained in high yields. The acetylene moiety in 1 slightly hindered the polymerization of the methacrylate moiety in the radical polymerization. The influences of the acetylene moiety decreased with the introduction of substituents at the acetylene moiety. The polymer reaction of the obtained polymer (2) having the acetylenic side chain with thiols gave the corresponding polymers having b-alkylmercaptoenoate moieties in high yields. As the polymers (2) having acetylene moieties activated by an electron-withdrawing group are a novel reactive polymer, studies on other polymer reactions and applications of 2 are in progress. References [1] W.T. Ford (Eds.), Polymeric Reagents and Catalysts, (ACS Symp. Ser., 308), Am. Chem. Soc., 1986; [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] D.C. Sherrington, P. Hodge (Eds.), Syntheses and Separations Using Functional Polymers, Wiley, 1988; J.L. Benham, J.F. Kinstle (Eds.), Chemical Reactions on Polymers, (ACS Symp. Ser., 364), Am. Chem. Soc., 1988; M. Lazar, T. Belha, J. Rychly, Chemical Reactions of Natural and Synthetic Polymer, Ellis Horwood, 1989; A. Akelah, A. Moet, Functionalized Polymers and Their Applications, Chapman & Hall, 1990. D. Barton, W.D. Ollis (Eds.), Comprehensive Organic Chemistry, vol. 1, Pergamon, 1979, p. 197. R. Scheffold (Ed.), Modern Synthetic Method, VCH, 1992, p. 103; P. Perlmutter, Conjugate Addition Reactions in Organic Synthesis, Pergamon Press, 1992, p. 339. (a) H. Kuroda, I. Tomita, T. Endo, Macromolecules 28 (1995) 433; (b) H. Kuroda, I. Tomita, T. Endo, Macromolecules 28 (1995) 6020; (c) H. Kuroda, I. Tomita, T. Endo, J. Polym. Sci.: Part A: Polym. Chem. 34 (1996) 1597; (d) H. Kuroda, I. Tomita, T. Endo, Polymer 38 (1997) 3655; (e) H. Kuroda, I. Tomita, T. Endo, Polymer 38 (1997) 6049. (a) H.G. Viehe, Chemistry of Acetylenes, Marcel Dekker, 1969, 335; (b) Z. Machacek, Chem. Prum 16 (1966) 604; (c) K.W. Doak, J. Am. Chem. Soc. 72 (1950) 4681; (d) M. Gazith, M. Szwarc, J. Am. Chem. Soc. 78 (1957) 3339; (e) M.S. Kharasch, J.J. Jerome, W.H. Urry, J. Org. Chem. 15 (1950) 966. L. Brandsma, Preparative Acetylenic Chemistry, second ed., Elsevier, 1998, p. 101. L. Brandsma, Preparative Acetylenic Chemistry, second ed., Elsevier, 1998, p. 100. R.C. Parish, L.M. Stock, J. Org. Chem. 30 (1965) 927. The absorptions attributed to acetylene moiety in the IR spectra of insoluble 1 obtained at high concentrations were clearly observed in a similar way to the IR spectra of the soluble 1. The intensities of the absorptions were almost the same as with 2a obtained in the case of Run 3. From the results and the reaction properties of alkynes, the degree of gelation may be low. Although the consumption of methyl propiolate was confirmed from the 1H NMR spectrum, vinyl proton generation by the addition of radical species to the terminal CC triple bond was hardly observed. J. Inanaga, Y. Baba, T. Hanamoto, Chem. Lett. (1993) 241. An acetylenic skeleton is linear and rigid. From which, the apparent size of polymers containing acetylene moieties may be bigger compared with the size of common polymers such as polystyrene, assuming the molecular weight of both is the same. GPC is a way to determine the molecular weight from the difference in the apparent size for standard polymers. We think that the apparent size of polymers obtained by the polymer reaction may become compact by transforming the acetylenic skeleton to olefinic skeleton. A detailed investigation into the variation of molecular weight by the polymer reaction is in progress with applications of 2.