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α-Methylstyrene(α-MeSt) and 2, 3-dimethylbutadiene (DMB) were copolymerized in THF and in hydrocarbon solvents with n-BuLi. The copolymer produced at 60°C in THF was composed of almost equimolar amounts of α-MeSt and DMB, if α-MeSt was charged in excess. In the copolymer α-MeSt and DMB were considered to be arranged alternately, and DMB was incorporated in the form of 1, 4-structure. In the copolymerization below 60°C the copolymer composition was affected by the ratio of initial monomer concentrations. The content of α-MeSt in the copolymer increased with decreasing polymerization temperature and reached 91% at −78°C. The copolymerization at 30°C gave the copolymer composed of (2:1) α-MeSt and DMB under the existence of large excess of α-MeSt. It was presumed that the major part of the copolymer was composed of repeated sequences of [α-MeSt·α·MeSt·DMB]. In benzene a copolymer rich in DMB (71%) was obtained at 60°C. The addition of THF to the polymerization system in benzene decreased the content of DMB.

2,3-Dimethylbutadiene was polymerized in tetrahydrofuran with n-BuLi. The content of the 1,2-unit in the polymer varied with the polymerization temperature as follows: 86% at −78°C, 69% at −45°C, 54% at −30°C, and 48% at 0°C. The relationship between log (k1,2/k1,4) and 1/T showed a break at −30°C, where k1,2 and k1,4 are the propagation rate constants leading to the denoted structures, respectively, and T is the polymerization temperature (°K). It was postulated that the continuous arrangement of 1,2-units, which is preferential at low temperature, becomes impossible at higher temperatures due to steric hindrance, and the insertion of the 1,4-unit in the sequence of 1,2-units takes place more frequently, resulting in alternating arrangements of the 1,2- and 1,4-unit above −30°C. The NMR spectra of the polymers showed that the chemical shifts of each monomeric unit varied with the difference of the neighboring monomeric units in both sides. The spectrum of the polymer having a 1,2- and 1,4-unit in 1:1 suggested the 1,2-unit being held between the 1,4-units, i.e., both the units being alternate. The polymerization of 2,3-dimethylbutadiene in hydrocarbon solvent gave a polymer rich in the 1,4-unit with n-BuLi at 30°C, but formed a similar polymer with K-dispersion as that obtained with n-BuLi in tetrahydrofuran at 30°C.

o-Methoxy-α-methylstyrene (o-MeO-α-MeSt) was polymerized under various conditions using BF3OEt2, TiCl4, SnCl2, EtAlCl2, n-butyllithium (n-BuLi), or Na-naphthalene as catalysts, and methylene chloride, n-heptane, toluene, or tetrahydrofuran (THF) as solvents. Generally poly(o-MeO-α-MeSt) was formed below −30°C. The cationic polymerizations proceeded more rapidly than the anionic ones, which gave polymer only in a polar solvent such as THF. α-Methylstyrene (α-MeSt) was also polymerized for comparison with the tacticity of poly(o-MeO-α-MeSt). The stereoregularity of the polymer was investigated by NMR spectroscopy. Assignments of the α-methyl resonances of the polymers were made on the basis of the methylene resonances. In the NMR spectrum of poly(o-MeO-α-MeSt), the methyl groups showed three peaks at 4.45, 4.80, and 5.35 ppm on the high-field side from methylene chloride used as an internal standard; the peaks were assigned to isotactic (I), heterotactic (H), and syndiotactic (S) triad sequences with increasing magnetic field. The polymer obtained at −78°C from the anionic or cationic catalyst showed an S content higher than 74%, and the content decreased with an increasing polymerization temperature. The tacticities of the polymers formed in the cationic polymerizations depended only slightly on the catalyst and the solvent. The stereospecificity in the cationic polymerization was very similar to that of α-methylstyrene (α-MeSt) reported by Ohsumi et al.,1 whereas considerably different results were obtained in the anionic polymerization.