Three-Dimensional Polymer Micelles Formed by Crystallization-Driven Self-Assembly

Abstract

Polymer self-assembly plays a crucial role across various fields, such as biomedicine, catalysis, and optoelectronics. Over the years, self-assembly in solution has attracted significant interest. In 2007, our group, in collaboration with Prof. Ian Manners, published a groundbreaking article in Science on living crystallization-driven self-assembly (CDSA) of amphiphilic block copolymers featuring a crystalline core-forming block. This study focused on polyferrocenylsilane block copolymers (PFS BCPs). Living CDSA operates similarly to living polymerization, enabling the precise fabrication of micelles with predictable shapes and dimensions. The crystalline nature of the core-forming block promotes the formation of structures with low interfacial curvature, such as cylinders and platelets, which are rarely formed in traditional self-assembly techniques based on microphase separation.

Over the past two decades, we have pioneered a range of strategies to create one-dimensional (1D), 2D, 3D, and hierarchical uniform PFS BCP structures via CDSA. This method has also been extended to other semicrystalline polymer systems to produce regular and uniform assemblies. While 1D and 2D micelles have been extensively studied, the fabrication of 3D structures remains relatively rare. Nature, however, possesses exquisite 3D structures. Although CDSA has generated some 3D structures, it has not yet achieved the complexity found in nature. Researchers continue to push boundaries toward creating more intricate 3D structures.

In this Account, we summarize our research advancements on 3D structure fabrication via CDSA. The free energy of the system, influenced by various factors, ultimately determines micellar morphology and growth behavior. Our work has led to the formation of branched structures through multistep seeded growth processes, incorporating PFS homopolymers (HP) with PFS BCP, manipulating the cooling rate, adjusting the corona block composition, controlling polymer dispersity, and varying solvents. Further innovations involved the use of organic sacrificial templates to produce hollow fiber-basket polymersomes and the application of inorganic substrates for surface micelle growth, yielding organic–inorganic hybrid materials with tailored functionalities. A significant breakthrough was the development of protocols for generating uniform polymeric spherulites and their precursors in solution. Although spherulites are common in bulk polymer materials and materials found in fields such as geology and biology, they have not been observed from block polymers in solution. We uncovered a novel CDSA mechanism in which defects in lamellar precursors act as a critical driver for constructing 3D architectures. To achieve intricate, bioinspired, and uniform 3D structures, further efforts will focus on enhancing structural control and integrating multifunctional properties.