CHAIN TRANSFER-REACTION TO TERMINAL OLEFINS IN THE POLYMERIZATION OF 1-PHENYL-1-PROPYNE WITH NB AND TA CATALYSTS

Effects of various olefins as chain transfer agents were studied in th e polymerization of 1-phenyl-1-propyne catalyzed by NbCl5-Bu4Sn (1:2) (Bu:butyl) and TaCl5-Bu4Sn (1:2). In the Nb-catalyzed polymerization, Si-containing terminal olefins, especially butyldimethylvinylsilane an d dimethylphenylvinylsilane, proved to greatly lower the polymer molec ular weight; e. g., the number-average molecular weight (M(n)BAR) of t he polymer formed without an olefin was 2,0 . 10(5), whereas it decrea sed to 7 . 10(3) . 1 . 10(4), i. e., below 1/20 in the presence of the Si-containing olefins (1/5 equivalent to the monomer). In the Ta-cata lyzed polymerization, in contrast, hydrocarbon terminal olefins like 1 -octene were effective; e. g., while the M(n)BAR of the polymer reache d 4,0 - 10(5) without an olefin, the M(n)BAR was no more than 9 - 10(3 ) - 2 . 10(4), i. e., smaller than 1/25 in the presence of olefins. Po ly(1-phenyl-1-propyne) obtained using the Nb catalyst in the presence of butyldimethylvinylsilane possesses the terminal butyldimethylsilyl group derived from the added olefin. Thus, suitable olefins are useful to control the molecular weight of poly(1-phenyl-1-propyne) by chain transfer, which verifies the metal-carbene mechanism for the polymeriz ation of 1-phenyl-1-propyne by group 5 transition metal catalysts.