Practical Anionic Synthesis of in-Chain Functional Polymers By Homo- and Copolymerization of P- Dimethylsilylstyrene with Styrene

In order to develop a general, practical method for the anionic synthesis of in-chain functionalized homopolymers and block copolymers, the homo- and copolymerization of p-dimethylsilylstyrene (p-DMSS) with styrene have been investigated using n-butyllithium as initiator. When benzene was used as a solvent well-defined homo and copolymers were obtained; however, quite surprisingly when cyclohexane was used as solvent, chain-branching reactions were detected. Chain-branching reactions increased with reaction time, reaction temperature, Lewis base content and p-DMSS level, independently of the deactivating agent used (BHT, methanol, methanol/HCl, methanol/acetic acid, trimethylchlorosilane, methyl iodide).

In order to determine if 1,6 elimination reactions were promoting the undesired chain-branching reactions, m-dimethylsilylstyrene (m-DMSS) was synthesized and tested under same conditions as before.  Surprisingly, chain-branching reactions persisted as indicated by polydispersity index increases with time and by Maldi-TOF mass spectrometry results. It is proposed that for the case of m-DMSS chain-branching reactions occur by a silyl hydride displacement mechanism. Efforts to diminish or to eliminate chain-branching reactions when using p-DMSS have been investigated and will be the subject of future publications.