2‐Methylbutene‐1, 2‐methylpentene‐1, and 2,3‐dimethylbutene‐1 were polymerized by AlCl3 or AlBr3 catalyst in ethyl chloride or ethyl chloride—vinyl chloride mixtures at temperatures down to —175°C. The glass transition temperatures of the amorphous polymers are −5, 27, and 37°C., respectively. The highest molecular weights—weight averages about 200,000 to 350,000—were found at the lowest polymerization temperature and with monomer—catalyst molar ratios of about 1000 and over. The influence of the addition of the corresponding 2‐methylalkene‐2 was investigated for the polymerization of 2‐methylbutene‐1 and 2‐methylpentene‐1. The other alkenes investigated, viz., 2,3,3‐trimethylbutene‐1, 2,4,4‐trimethylpentene‐1, and 2‐ethylbutene‐1, yielded only small amounts of liquid oligomers. In the polymerization of 2,3‐dimethylbutene‐1 an extensive intramolecular 3–2 hydride shift occurred, varying in amount from 80% at −125°C. to 100% at −175°C., to judge from NMR and infrared spectra. Of the methylenecycloalkanes investigated, only methylene—cyclohexane yielded a high molecular weight polymer—weight average molecular weight about 100,000—although in a yield of only a few per cent, under optimal conditions at −180°C. Methylenecyclobutane gave a semisolid polymer of low molecular weight, methylenecyclopentane a small amount of liquid oligomers, and 2‐, 3‐, and 4‐methyl(methylenecyclohexane) solid polymers of low molecular weight. Poly(methylenecyclohexane) and the polymer from 4‐methyl(methylenecyclohexane) crystallized from solution or upon thermal treatment; the crystalline melting points were about 210 and 195°C., respectively. The relation between structure and ease of polymerization of this type of unsaturated aliphatic hydrocarbon is briefly discussed.
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