Amphiphilic Rod-Rod Block Copolymers Based On Phenylacetylene And 3,5-Disubstituted Phenylacetylene: Synthesis, Helical Conformation, And Self-Assembly

A novel series of amphiphilic rod-rod block copolymers (PPA(m)-b-PrmEO(n)) based on achiral phenylacetylene (PA) and chiral I 3,5-disubstituted phenylacetylene (rmEO) were synthesized through sequential living polyrnerizaitons using the catalyst Rh[C(C6H5)=C(C6H5)(2)](nbd)(4-FC6H4)(3)P (nbd = norbornadiene) (Rh-cat). The living nature of the polymerization of rmEO using Rh-cat was proved. These block copolymers consist of a hydrophobic achiral stretched cis-transoid helical PPA block and a hydrophilic one-handed contracted cis-cisoid helical PrmEO block. The amphiphilic block copolymers could self assemble into well-defined aggregates in THE/H2O. The effects of the composition of block copolymers, water contents, and initial copolymer concentration on the formation of aggregates were investigated. The block copolymers with short corona-forming blocks formed vesicles, while those with long corona-forming blocks formed novel multiarm worm-like micelles. As the water content increased, the aggregates transformed from the spherical micelles to worm-like micelles, and then the end-caps of the worm-like micelles fused together to form the multiarm worm-like micelles. The formation mechanism of the multiarm worm-like micelles was proposed by considering the large end-capping energy originating from the rigid conformation of the copolymers. Besides, the copolymers tend to form vesicles at high initial copolymer concentration.