Synthesis of carbon-carbon chain polymer by phase-transfer-catalyzed polycondensation of α,α′-dichloro-p-xylene with t-butyl cyanoacetate

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Synthesis of carbon-carbon chain polymer by phase-transfer-catalyzed polycondensation of α,α′-dichloro-p-xylene with t-butyl cyanoacetate

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  SYNTHESIS OF CARBON-CARBON CHAIN POLYMER BY PHASE-TRANSFER-CATALYZED POLYCONDENSATION OF a,a'-DICHLORO-pXYLENE WITH t-BUTYL CYANOACETATE Recently, phase-transfer catalysis technique using quaternary ammonium salts and crown ethers has been widely used for organic synthesis, particularly for nucleophilic substitution reactions (1,2). Our attention has been focused on the application of this technique to polymer synthesis, and we have suc- cessfully synthesized various types of condensation polymers such as aromatic polysulfonates (3,4), aromatic polyethers 9, liphatic polysulfides (6), and aromatic polyphosphonates 7) by phase-transfer-catalyzed polycondensation. In a continuation of these studies, we have extended phase-transfer-cata- lyzed alkylation to aliphatic nucleophilic substitution polymerization using carbanion of t-butyl cyanoacetate as a nucleophile. We now wish to report a successful synthesis of carbon-carbon chain polymer by phase-transfer-cata- lyzed polycondensation of a,a'-dichloro-p-xylene with t-butyl cyanoacetate in benzene-aqueous alkaline solution system, as shown in eq. (1). 7H3 2-11 F lCH2-@H2Cl + NC-CH C-0- CH3 0 CH3 CN Catalyst CgH6/aq.alkali Few works have been disclosed to date on the preparation of this type of hydrocarbon polymers; the only examples known are the polycondensation of bischloromethyl aromatic compounds with malononitrile using sodium hydride 8) or triethylamine 9) as base in dimethyl sulfoxide. Results and Discussion A typical procedure for the polycondensation is as follows: To a solution of 0.353 g (2.5 mmole) of t-butyl cyanoacetate in 5 ml of 50 wt aqueous sodium hydroxide were added 0.438 g (2.5 mmole) of &,a'-dichloro-p-xylene and 1 ml of benzene. To the mixture was added 0.29 g (1.25 mmole) of benzyltriethylammonium chloride; this was stirred at 50°C for 2 hr. The polymer-benzene layer separated from the aqueous layer as the polymerization proceeded. The aqueous layer was then decanted and the polymer layer was washed repeatedly with water to remove the sodium chloride that formed and the excess sodium hydroxide. It was diluted with N-methyl-2-pyrrolidone (NMP) giving a clear solution, which was subsequently poured into 500 ml of 0.1 M hydrochloric acid. The polymer that precipitated was collected, washed Journal of Polymer Science: Polymer Letters Edition Vol. 19, 205-210 (1981) 1981 John Wiley Sons Inc. CCC 0360-6 3 84/81 040205-06 0 1 OO  206 POLYMER LETTERS EDITION 0.8 - L l- 0.6 5 v I 0 4 [ w z 0.2 0 20 4 60 80 100 TEMPERATURE oc) Fig. 1. Effect of reaction temperature on inherent viscosity of the polymer formed in the polycondensation with BTEAC catalyst (50 mole ) in a ben- zene-50 wt aqueous sodium hydroxide system: (A) the (B) for 6 hr. > 0.8 t v, 0.6 w 0 4 ul > I [ W z 0 2 0 reaction for 2 hr, 20 30 40 50 CONCENTRATION OF AQ. NaOH (wt ) Fig. 2. Effect of concentration of aqueous sodium hydroxide on inherent viscosity of the polymer formed in the polycondensation with BTEAC catalyst 50 mole ) in a benzene-water system: (A) the reaction at 20°C for 6 hr, (B) at 50°C for 2 hr. thoroughly with water, and dried in vacuo at 60°C. It weighed 0.577 g (95 ). Inherent viscosity of the polymer in NMP was 0.52 dl/g, measured at a con- centration of 0.5 g/dl at 30°C. ANAL.Calcd for (Cl5Hl7NO2),,: C 74.05 ; H, 7.04 ; N, 5.76 . Found: C, 74.5 ; H, 6.8 ; N, 5.5 . The structure of the polymer formed was identified as the hydrocarbon  POLYMER LETTERS EDITION 207 0.8 0.6 w + 0 4 W 0.2 01 0 25 50 75 100 125 AMOUNT OF CATALYST (mole ) Fig. 3. Effect of amount of BTEAC catalyst on inherent viscosity of the polymer formed in the polycondensation in benzene-50 wt aqueous sodium hydroxide system at 50°C for 2 hr. TABLE I Synthesis of Polymer in Various Aromatic Solvent-Water Systems with BTEAC Catalysta Polymer Solvent Yield, yinhb Benzene 87 0.73 Toluene 87 0.36 p-Xylene 89 0.32 Anisole 85 1.60 Benzonitrile 85 0.77 aThe polymerization was carried out with 2.5 mmole of the monomers in the presence of 1.25 mmole of BTEAC in 1 ml of benzene and 5 ml of 50 wt aqueous sodium hydroxide at 20°C for 6 hr. bMeasured at a concentration of 0.5 g/dl in NMP at 30°C. polymer proposed in eq. (1) by means of infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy and elemental analyses. The IR spectrum (film) exhibited characteristic absorptions at 2240 (EN), 1730 (C=O), 1 150 (C-0), and 840 cm-' (p-phenylene). The NMR spectrum in DMSO-d6 solu- tion showed three singlets at 6 1.20 (9H, methyl), 3.1 8 4H, ethylene), and 7.13 (4H, phenylene).  208 POLYMER LETTERS EDITION TABLE I1 Synthesis of Polymer with Various Phase-Transfer Catalysts in a Benzene-Water Systema Tinh of polymerb Reaction Alkaline component Catalyst time, hr NaOH KOH TMAC TEAC TBAC BTEAC CTMAC 15-C-5 18-C-6 DB-18-C-6 DC-18-C-6 DB-24-C-8 DC-24-C-8 2 2 2 2 2 4 5 2 3 3 4 0.14 0 68 0.93 0.52 0.47 0.24 0.37 0.20 0.17 0.17 0.19 0.13 0.21 0.22 0.30 0.16 0.21 0.27 0.05 0 06 0.04 0.17 aThe polymerization was carried out with 2.5 mmole of the monomers in the presence of 1.25 mmole of the catalyst in 1 ml of benzene and 5 ml of 50 w 7 aqueous sodium hydroxide at 50°C. bMeasured at a concentration of 0.5 g/dl in NMP at 30°C. In general, phase-transfer-catalyzed alkylation of diethyl malonate or ethyl acetoacetate using aqueous sodium hydroxide has not been successful because of rapid ester hydrolysis (10). To avoid hydrolysis problems, t-butyl ester of cyanoacetic acid was used here as a nucleophilic monomer. The two-phase polycondensation was carried out with various types of phase-transfer catalysts: quaternary ammonium salts such as tetramethylammo- nium chloride (TMAC), tetraethylammonium chloride (TEAC), tetrabutylam- monium chloride (TBAC), benzyltriethylammonium chloride (BTEAC), and cetyltrimethylammonium chloride (CTMAC), and crown ethers such as 15- crown-5 (1 5-C-5), 18-crown-6 1 8-C-6), dibenzo-18-crown-6 (DB-18-C-6), di- cyclohexyl-18-crown-6 (DC-18-C-6), dibenzo-24-crown-8 (DB-24-C-8), and di- cyclohexyl-24-crown-8 (DC-24-C-8). The effect of reaction temperature on inherent viscosity of the resulting polymer was first examined and the results are shown in Figure 1. The reac- tion product prepared at 80°C contained hydrolyzed structure to some extent,  POLYMER LETTERS EDITION 209 1.0 012345 REACTION TIME (hr.) Fig. 4. Time dependence of inherent viscosity of the polymer formed in the polycondensation with various catalysts 50 mole ) in benzene-50 wt aqueous sodium hydroxide system at 50°C: (A) the reaction with BTEAC catalyst, (B) with 1842-6 catalyst. which was evidenced by the decrease in intensity of ester carbonyl absorption in the IR spectrum. The polycondensation at 10°C was too slow to afford a high-molecular-weight polymer. Therefore, the optimum range of reaction temperature was found to be 20 - 50°C. Figure 2 shows the influence of sodium hydroxide concentration in the aqueous solution on the inherent viscosity. High sodium hydroxide concentra- tion of 50 wt , which is conveniently used for general phase-transfer-cata- lyzed alkylation 10,l l), was necessary to prepare the polymer with high mo- lecular weight. n essential feature of this type of polycondensation is that relatively large amounts of the phase-transfer catalyst (at least 50 mole ) based on mono- mers is required to yield a high-molecular-weight polymer, as shown in Figure 3. This presents a striking contrast to the fact that only catalytic amounts of such a compound are necessary in the usual phase-transfer-catalyzed polycon- densation reported previously (3-7). As can be seen in Table I some aromatic solvents such as anisole and ben- zonitrile, as well as benzene, were used effectively for the preparation of the high-inherent-viscosity polymer. The influence of catalysts and alkaline components on the polycondensa- tion are summarized in Table 11, and progress of the polycondensation with different catalysts is given in Figure 4. Among these catalysts, the two-phase polycondensation was strongly catalyzed by some quaternary ammonium salts such as TEAC, TBAC, BTEAC, and CTMAC, leading to the formation of a high-molecular-weight polymer. All of the crown ethers were found to be less effective than the quaternary ammonium salts. In the two-phase system, sodi- um hydroxide as alkaline component in the aqueous phase was generally more
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