Anionic polymerization of 2-vinylpyridine by using 2,3-diphenyl-1,3-butadiene-magnesium complex as initiator

By using a divalent anionic initiator like a Grignard reagent, 2,3-diphenyl -1,3-butaditadiene-magnesium complex (DPB-Mg), living polymerization of 2-v inylpyridine (2-VP) was investigated. The polymerization of 2-VP with DPB-M g proceeded smoothly both at 0 degrees C in tetrahydrofuran (THF) and at 5 degrees C in benzene, but not in a living manner. Addition of hexamethylpho sphoramide (HMPA) led to acceleration of the polymerization rate and a smal l M-w/M-n (less than or equal to 1.4) value of the resulting polymer. As [H MPA]/[DPB-Mg] ratio was increased, the initiator efficiency (f) was remarka bly improved up to 1.0 in benzene and 0.88 in THF. However, the f value bec ame constant in a range of [HMPA]/[DPB-Mg] > 1, suggesting that the real ac tive species maybe an equimolar complex of DPB-Mg and HMPA. The living natu re of growing polymer was also confirmed by the quantitative termination wi th trimethylchlorosilane and the successive increment of the monomer. The l iving polymerization with this initiator could be achieved at a limited tem perature. The polymer obtained at -10 degrees C in THF or at room temperatu re in benzene exhibited two separate peaks in GPC or a very broad peak, res pectively.