Living Crystallization-Driven Self-Assembly of Linear and V-Shaped Oligo(p-phenylene ethynylene)-Containing Block Copolymers: Architecture Effect of p-Conjugated Crystalline Segment

Diblock copolymers (BCPs) with a pi-conjugated block and an appropriate block ratio can undergo crystallization driven self-assembly (CDSA) to form fiber-like micelles of uniform width and length. Almost all examples in the literature involve BCPs with a linear pi-conjugated block. We are interested in exploring the influence of the architecture of the pi-conjugated block on (living) CDSA of oligo(p-phenylene ethynylene) (OPE) BCPs with a common block length and the same corona-forming block. Herein, we designed and synthesized three OPE7-b-PNIPAM(22) BCPs with seven repeats in the OPE block, PNIPAM = poly(Nisopropylacrylamide), with a mean degree of polymerization of 22 which differed only in the architecture of the OPE block. One sample, the reference, had a linear OPE7 block. A second sample had a V-shaped OPE(7 )with PNIPAM(22) attached in the middle (mVOPE(7)), and the third sample was V-shaped with PNIPAM(22) attached at one end (tV-OPE7). Self-assembly experiments in ethanol/ water mixtures led to micelle-like aggregates. The variation of architecture of OPE7 backbone of OPE7-b-PNIPAM(22) led into distinct packing modes and different morphologies of the resulting aggregates. Self-seeding experiments with L-OPE7-b-PNIPAM(22 )gave monodisperse fiber-like micelles of uniform width and tunable length, whereas irregular aggregates or polydisperse ribbon-like micelles were formed by tV-OPE7-b-PNIPAM(22) and mV-OPE7-b-PNIPAM(22). Important differences were also found in seeded growth experiments designed to form block comicelles with a heterogeneous core junction. L-OPE7-b-PNIPAM(22) could efficiently deposit onto the L-OPE9 core of L-OPE9-b-P2VP(56) seed micelles (P2VP = poly(2-vinylpyridine) to form triblock comicelles. In contrast, neither mV-OPE7-b-PNIPAM(22 )nor tV-OPE7-b-PNIPAM(22) was able to grow micelles from the ends of the L-OPE9-b-P2VP(56) seed micelles. Instead, they formed polydisperse micelles by a self-nucleation and growth process. This work provides instructive information about how the architecture of pi-conjugated blocks affects the CDSA of BCPs with a pi-conjugated-polymer block, especially under especially self-seeding and heterogeneous seeded growth protocols.

Automated summary

This study investigates the influence of different architectures of pi-conjugated blocks on the crystallization-driven self-assembly (CDSA) of BCPs. The results show that different block architectures can lead to different aggregate morphologies. Furthermore, experiments on heterogeneous seeded growth reveal differences in the behavior of BCPs with different architectures.