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

Abstract

Diblock copolymers (BCPs) with a π-conjugated block and an appropriate block ratio can undergo crystallizationdriven self-assembly (CDSA) to form fiber-like micelles of uniform width and length. Almost all examples in the literature involve BCPs with a linear π-conjugated block. We are interested in exploring the influence of the architecture of the π-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 OPE 7 -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 OPE 7 block. A second sample had a V-shaped OPE 7 with PNIPAM 22 attached in the middle (mV-OPE 7 ), and the third sample was V-shaped with PNIPAM 22 attached at one end (tV-OPE 7 ). Self-assembly experiments in ethanol/ water mixtures led to micelle-like aggregates. The variation of architecture of OPE 7 backbone of OPE 7 -b-PNIPAM 22 led into distinct packing modes and different morphologies of the resulting aggregates. Self-seeding experiments with L-OPE 7 -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-OPE 7 -b-PNIPAM 22 and mV-OPE 7 -b-PNIPAM 22 . Important differences were also found in seeded growth experiments designed to form block comicelles with a heterogeneous core junction. L-OPE 7 -b-PNIPAM 22 could efficiently deposit onto the L-OPE 9 core of L-OPE 9 -b-P2VP 56 seed micelles (P2VP = poly(2-vinylpyridine) to form triblock comicelles. In contrast, neither mV-OPE 7 -b-PNIPAM 22 nor tV-OPE 7 -b-PNIPAM 22 was able to grow micelles from the ends of the L-OPE 9 -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 π-conjugated blocks affects the CDSA of BCPs with a π-conjugated-polymer block, especially under especially self-seeding and heterogeneous seeded growth protocols.

Synthesis and living crystallization-driven self-assembly of backbone asymmetric and symmetric π-conjugated oligo(p-phenylene ethynylene)-based block copolymers

“…The length of the resulting comicelles appeared to increase linearly with n unimer / n seed , which was shown in our previous report. 58 The seeded growth protocol used for S-OPE 7 - b -PNIPAM 22 was utilized for D-OPE 7 - b -PNIPAM 22 , given the structural similarity between S-OPE 7 and D-OPE 7 . The appearance of the wider and darker central block flanked by one or two gray ends indicated that segmented diblock and triblock comicelles were formed from the seeds of S-OPE 9 - b -P2VP 56 with a width of 23 nm as indicated by purple arrows in Fig.…”

Modulating living crystallization-driven self-assembly behaviors of oligo(p-phenylene ethynylene)-containing block copolymers and micellar stability by solvent and corona-forming chain length

“…π-Conjugated core-forming OPE 7 with an alkyne chain end with a molecular weight of 2187 g mol −1 was first prepared by the iterative Sonogashira coupling reaction, followed by chain end modification according to our previous reports. 46,47 Corona-forming PNIPAM chains of different lengths were prepared by atom transfer radical polymerization (ATRP) from azide-containing initiators. 47 Subsequently, OPE 7 - b -PNIPAM n ( n = 8, 22 and 47) BCPs with low polydispersities ( M w / M n ≤ 1.18) were obtained by Cu-catalyzed alkyne/azide cycloaddition reactions (Scheme 1, Fig.…”

Crystallization-Driven Solution-State Assembly of Conjugated Block Copolymers in Materials Science

“…Given the propensity for most conjugated polymer building blocks to exhibit strong π–π interactions and crystallize easily, living CDSA presents a promising avenue for the diverse conjugated BCPs. Specifically, various conjugated core-forming blocks have been reported, including P3HT, − , poly­(di- n -hexylfluorene) (PDHF), , poly­(3-decylselenophene) (P3DSe), oligo­( p -phenylene­ethynylene) (OPE), , and oligo­( p -phenylene­vinylene) (OPV), ,, which have been the focus of numerous studies aimed at controlling the nanostructures using living CDSA techniques.…”