Morphological Transitions in the Crystallization-Driven Self-Assembly of Narrowly Distributed π-Conjugated Triblock Copolymer

Abstract

Crystallization-driven self-assembly (CDSA) of π-conjugated block copolymers enables precise control over micellar morphology. However, generalizable strategies for preparing π-conjugated polymers with narrow dispersity (Đ < 1.3) to ensure reproducible self-assembly remain scarce. Herein, we report ABA triblock copolymers consisting of a crystalline poly(p-phenylene) core flanked by two pH responsive poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) coronae, synthesized via controlled step-growth polymerization and atom-transfer radical polymerization. In tetrahydrofuran-water mixtures, these copolymers undergo CDSA to form micelles exhibiting a progressive morphological evolution, from ribbons to fibers and ultimately to spherical aggregates, as the corona length increases, in accordance with a monotonic rise in interfacial curvature. Notably, the PDMAEMA coronae confer pronounced pH responsiveness. Under acidic conditions, CDSA is suppressed and curvature enhanced transitions toward spherical geometries are driven by electrostatic repulsion among protonated coronal segments. In contrast, alkaline media promote hydrophobic clustering of deprotonated chains, inducing ribbon stacking and longitudinal elongation of the fibrous assemblies.