Effect of Lithium Perchlorate on the Spontaneous Copolymerization of 4-Vinylpyrdine with Various Electron-Rich Vinyl Monomers

摘要

The spontaneous copolymerization of 4-vinylpyridine(4-VP) activated with lithium perchlorate (LiClO_4) with various electron rich monomers (p-methoxustyrene, MeOSt; p-methylstyrene, MeSt; styrene, St) was investigated in variou solvent systems at 75degC. Increasing the LiClO_4 concentration and the nucleophilicity of the electron rich monomer increased the copolymer yields. Both ~1H-NMR and elemental analysis confirmed the almost 1:1 copolymer structure for VP/MeOSt system which possessed high molecular weigh and narrow polydispersity (PDI). Compared to 4-VP activated with zinc chloride, LiClO_4 systems showed slightly lower yields and much narrowed PDI. We also investigated the spontaneous copolymerization of 4-VP activated with various protic acids in the reaction with various electron rich comonomers. However, generally protic salt forms showed less solubility in organic solvents and showed low molecular weight polymer products with low yields. The proposed initiation mechanism exhibits the formation of a #sigma#-bond between the #beta#-carbons of the two donor-acceptor monomers, creating the 1,4-tetramethylene biradical intermediate initiating the copolymerization.