CHAIN TRANSFER-REACTION IN THE POLYMERIZATION OF SUBSTITUTED ACETYLENES .2. CHAIN TRANSFER-REACTION TO TRIMETHYLVINYLSILANE IN THE POLYMERIZATION OF DISUBSTITUTED ACETYLENES BY MOCL5-N-BU4SN

The effect of various olefins as chain transfer agents was studied in the polymerization of 1-chloro-1-octyne, 1-chloro-2-phenylacetylene, 2 -octyne, etc., catalyzed by MoCl5-n-Bu4Sn (1:1). Si-containing olefins , especially trimethylvinylsilane, greatly lowered the polymer molecul ar weight in the polymerization of the Cl-containing acetylenes, e.g., the M(n)BAR Of poly(1-chloro-1-octyne) was 4.2 X 10(5) without an ole fin, whereas it decreased to 3.4 X 10(4), i.e., below 1/10 in the pres ence of trimethylvinylsilane (1/2 equiv to monomer). In contrast, the molecular weight of poly(2-octyne) did not decrease that much, even wi th trimethylvinylsilane. The Cl-containing polyacetylenes obtained in the presence of trimethylvinylsilane as chain transfer agent possessed the trimethylsilyl group. Thus, the present study enables control of the molecular weight of substituted polyacetylenes by chain transfer, and further verifies the metal carbene mechanism for the polymerizatio n of substituted acetylenes.