Synthesis and self-seeding behavior of oligo(p-phenylene vinylene)-b-poly(N-(2-hydroxypropyl)methacrylamide)
Self-seeding of living crystallization-driven self-assembly (CDSA) has been considered to be one of the most attractive strategies to fabricate well-defined fiber-like nanostructures with excellent control over their length and composition. To extend the scope of self-seeding of oligo(p-phenylene vinylene) (OPV)-based copolymers, the poly(N-(2-hydroxypropyl) methacrylamide) (PHPMA) segment with proven biocompatibility, synthetic flexibility and well-developed conjugation chemistry, which was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization using an azide-containing chain transfer agent, was coupled with the alkyne-terminated OPV block by a copper-catalyzed alkyne–azide cycloaddition reaction. All OPV5-b-PHPMA (OPV5-b-PHPMA36, OPV5-b-PHPMA71 and OPV5-b-PHPMA100, the subscripts represent the number of repeat units of each block) with the same crystallizable core-forming OPV segment but different corona-forming PHPMA blocks of various chain lengths can self-assemble in ethanol to form fiber-like micelles with a length of several micrometers by a direct heating and cooling process. Uniform fiber-like micelles with a length up to ∼1 μm can be easily prepared by temperature-induced self-seeding of OPV5-b-PHPMA71. However, for self-seeding of OPV5-b-PHPMA36, ribbon-like nanostructures with a uniform and controllable length were formed, whereas relatively short fiber-like micelles with broad length distributions were formed under similar conditions for OPV5-b-PHPMA100. These results indicated that the length of the PHPMA segment played an important role in determining the self-seeding behavior of OPV5-b-PHPMA.