Living Crystallization-Driven Self-Assembly of Oligo(p-phenylene vinylene)-Containing Block Copolymers: Impact of Branched Structure of Alkyl Side Chain of π-Conjugated Segment

The structure of side chains of pi-conjugated segments is a critical factor determining living crystallization-driven self-assembly (CDSA), a versatile platform to generate fiber-like nanostructures with precise length and composition. Herein, we design and synthesize three block copolymers (BCPs) containing same corona-forming poly(N-isopropyl acrylamide) (PNIPAM) segment, but different core-forming pi-conjugated oligo(p-phenylene vinylene) (OPV) with linear pentyl (l-OPV), racemic 2-methyl butyl (r-OPV) and stereo-regular chiral (S)-2-methyl butyl (c-OPV) side chains, respectively. By using these BCPs of l-OPV-b-PNIPAM47, r-OPV-b-PNIPAM47 and c-OPV-b-PNIPAM47 as model, we aim to get a deep insight into how steric and stereo-regular effect induced by branched alkyl side chains of OPV segment affects the living CDSA. The results showed that l-OPV-b-PNIPAM47 exhibits typical characteristics of self-seeding and seeded growth of living CDSA to give uniform fiber-like micelles of controlled length. On the contrary, r-OPV-b-PNIPAM47 and c-OPV-b-PNIPAM47 with branched racemic and stereo-regular chiral alkyl side chains are more prone to self-nucleation during the micellar elongation to give short and polydisperse fiber-like micelles. The obvious self-nucleation during the micellar elongation of r-OPV-b-PNIPAM47 and c-OPV-b-PNIPAM47 is due to the increase of steric repulsion with OPV units induced by branched alkyl side chains, not the stereo-irregular effect of racemic alkyl side chains.