Synthesis and characterisation of methoxysilyl terminated polybutadienes

Polybutadienyllithium systems with M¯_n in the range 1.5 × 10³-20 × 10³ are formed in hydrocarbon solvents by using n-butyllithium or 3-dimethylamino-propyllithium as initiator. These 'living' polymers, of low polydispersity and relatively high 1,4-structure, react with 3-chloropropyl(trimethoxy)silane at < -20°C, in the presence of tetrahydrofuran, to give, primarily, polymers terminated by the 3-chloropropyl(dimethoxy)silyl group, Si(OMe)₂{(CH₂)₃Cl}, as characterised by GPC and by ¹H, ¹³C and ²⁹Si NMR studies. Quaternisation by iodomethane of the telechelic polybutadiene with a dimethylamino end-group produces a silylated cationomer containing the terminal functionality, I^-+Me₃N(CH₂)₃. In some silylation reactions of polybutadienyllithium systems, especially at higher temperatures, and in related reactions with Si(OMe)₄, polymers coupled via the silyl groups are also formed. Hydrolysis of the terminal dimethoxysilyl functions occurs under acidic or basic conditions; end-group coupling to silica gel also occurs and other reactions have been investigated.