Polymer extended-chain crystals: Preparation, formation mechanisms and performances

Abstract

Polymer extended-chain crystals (ECCs) have garnered significant attention due to their exceptional thermodynamic stability, high melting temperatures, and superior mechanical and functional properties compared to folded-chain crystals (FCCs). This review systematically examines the preparation strategies, formation mechanisms, and performance characteristics of ECCs across various polymer systems. Key methodologies for ECC fabrication include crystallization during polymerization, high-pressure and high-temperature crystallization, shear-assisted crystallization, crystallization in Langmuir-Blodgett film. These approaches address critical challenges such as chain entanglement and entropy penalties, enabling the alignment of polymer chains into extended conformations. Notably, ECCs exhibit enhanced mechanical strength (e.g., ultrahigh-modulus polyethylene fibers), solvent resistance (e.g., poly(butylene succinate) ECC films), and electronic functionalities (e.g., piezoelectricity in poly(vinylidene fluoride) ECC specimens). However, achieving pure ECC structures under atmospheric pressure remains challenging due to kinetic limitations of ECCs and thermodynamic advantages of FCCs. Emerging strategies, such as inclusion complex templating crystallization, demonstrate potential for reducing processing constraints. The review also highlights specialized ECCs in conjugated polymers, cyclic polymers, and oligomers, emphasizing structure-property relationships. Despite advancements, scalability and energy-efficient production require further optimization. Future efforts should focus on elucidating nucleation kinetics, integrating multifunctional properties, and expanding applications in high-performance and versatile functional materials.