Synthesis and Characterization of Narrow Molecular Weight Distribution AB and ABA Poly(vinylpyridine)−Poly(dimethylsiloxane) Block Copolymers via Anionic Polymerization

Abstract

The synthesis is described of AB and ABA narrow molecular weight distribution poly(2-vinylpyridine)−poly(dimethylsiloxane) (P2VP−PDMS) and poly(4-vinylpyridine)−poly(dimethylsiloxane) block copolymers. Three synthesis methods were explored. The first and most general procedure (method 1) involves the anionic polymerization of 2VP or 4VP initiated by an acetal-functionalized alkyllithium. Acid hydrolysis of the acetal and titration of the resulting hydroxyl group with triphenyllithium gave a lithium alkoxide end group. This functionality was used to initiate hexamethylcyclotrisiloxane (D3), giving the living P2(4)VP-b-PDMSLi block copolymers that were terminated or coupled with trimethylchlorosilane and dimethyldichlorosilane, respectively, to give the AB and ABA block copolymers. An alternative synthesis (method 2) applicable only to the synthesis of P2VP-b-PDMS or P2VP-b-PDMS-b-P2VP involved alkylation of the lithium P2VP anion with a bromo-functionalized acetal. Acetal hydrolysis and titration with triphenylmethyllithium gave the lithium alkoxide end-functionalized P2VP that was used to initiate D3 followed by termination or coupling with trimethylchlorosilane and dimethyldichlorosilane, respectively. P2VP−PDMS block copolymers could also be synthesized (method 3) by end-capping of living P2VPLi with 2-isopropenylpyridine followed by addition of 1 equiv of ethylene oxide. Addition of D3 to the resulting lithium alkoxide and coupling with trimethylchlorosilane or dimethyldichlorosilane gave the desired AB and ABA block copolymers.