[Show abstract][Hide abstract] ABSTRACT: Polymerizations of various methacrylates and α-(p-substituted phenyl)acrylates were studied in toluene and tetrahydrofuran by several anionic initiators. The polymerization with octylpotassium in tetrahydrofuran was found to be the most suitable for the formation of the heterotactic polymer, defined as the polymer containing more than 50% heterotactic triads. Methacrylic acid esters of the primary alcohol gave the heterotactic polymers, whose heterotactic contents increased with an increase in the bulkiness of the ester group. Methacrylic esters of secondary alcohol generally gave heterotactic polymers with octylpotassium in tetrahydrofuran. In the polymerizations of methacrylic acid esters of tertiary alcohol, the heterotactic contents decreased with an increase in the bulkiness of the ester group. A perfectly atactic polymer was obtained in the polymerization of methyl α-phenylacrylate with butyllithium in tetrahydrofuran, but it gave the heterotactic polymer when initiated with octylpotassium in tetrahydrofuran. Methyl α-p-chlorophenylacrylate produced the heterotactic polymer in tetrahydrofuran with butyllithium as well as with octylpotassium. In the case of methyl α-p-bromophenylacrylate, the heterotactic polymer was obtained even in the polymerization in toluene with butyllithium. These results indicate that the acrylic acid ester having the bulkier substituent tends to give the heterotactic polymer more easily by anionic initiator.
[Show abstract][Hide abstract] ABSTRACT: The polymerization of ethyl methacrylate (EMA) with t-C4H9MgBr in toluene at low temperature gave a highly isotactic polymer as in the case of living and highly isotactic polymerization of methyl methacrylate (MMA) with t-C4H9MgBr. Although the molecular weight distribution (MWD) of the poly(EMA) was bimodal, both species giving higher and lower molecular weight fractions contributed to the formation of highly isotactic block copolymers with bimodal MWD, indicating the living nature of both species. The polymerization of EMA with the living anion of isotactic PMMA formed with t-C4H9MgBr gave a highly isotactic block copolymer with unimodal MWD. This suggests that the multiplicity of active species observed in the polymerization of EMA with t-C4H9MgBr was caused by the initiation of EMA with t-C4H9MgBr. Conventional copolymerization of EMA and MMA afforded a highly isotactic copolymer with bimodal MWD, confirming the above consideration. 13C NMR spectrum of the copolymer indicated the comonomer sequence to be random. Glass transition temperatures of the isotactic and syndiotactic copolymers of EMA and MMA could be changed from 8 to 120°C by changing composition and tacticity.
[Show abstract][Hide abstract] ABSTRACT: Polymerizations of ethyl methacrylate were carried out in toluene with butyllithium at various temperatures. The polymer obtained at −78°C could be fractionated into methanol-insoluble and methanol-soluble fractions. The former was rather syndiotactic. The latter was found by gel-permeation chromatography and 1H NMR spectroscopy to be composed of highly isotactic polymer and isotactic oligomer. These three fractions were formed simultaneously at the beginning of the polymerization and the amounts and molecular weights of the isotactic and syndiotactic fractions increased during the polymerization, while the amount of oligomeric fraction remained almost constant after the initial rapid increase. These results indicate the coexistence of three different active species for isotactic and syndiotactic polymers and isotactic oligomer, respectively, at the initial stage of the polymerization and two propagating species during the polymerization. The amounts of syndiotactic fraction and oligomeric fraction decreased with an increase in the polymerization temperature and only the isotactic polymer was obtained above −20°C. When the polymerization was initiated with 1,1-diphenylhexyllithium, only an isotactic polymer was produced. In the polymerization initiated with butyllithium, an appreciable amount of lithium ethoxide formed at the initial stage of the reaction, but no formation of the ethoxide was observed in the case of 1,1-diphenylhexyllithium. This indicates that the multiplicity of the active species in the polymerization with butyllithium is strongly related to the lithium ethoxide formed.
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