Quantitative Defect Engineering Governs Crystallization Pathways in Polymer Crystals

초록

Defect engineering is an emerging strategy for tailoring the structures and functionalities of inorganic crystalline materials. However, in polymer crystals, intrinsic structural complexities, such as chain folding and molecular weight distribution, often lead to less defined crystal structures, making both the quantitative introduction of defects and the systematic analysis of their effects highly challenging. Herein, we present a systematic strategy for defect control in crystalline polymers using rigid conjugated poly(cyclopentenylene vinylene) (PCPV) homopolymers containing fluorene units with either two (Di, D) or one (Mono, M) neo-hexyl side chain. This model system eliminates the common chain folding inherent to polymer crystallization, enabling direct investigation of defect-mediated crystallization behavior. Five series of random pDM copolymers were prepared with a fixed total degree of polymerization (DP) of 20 and varied D/M ratios. Increasing the M content effectively introduced defects relative to the fully substituted Di system. Despite these defects, all pDMs consistently crystallized into two-dimensional nanosheets. Notably, the higher defect fractions governed the crystallization pathway, selectively promoting crystal growth along the (100) direction and reducing the corresponding lattice d-spacing (d 200) from 16.1 to 15.6 & Aring;. Density functional theory (DFT) calculations further revealed that defect incorporation modulated the electrostatic potential (ESP) of the polymers, thereby altering the intermolecular interactions and crystalline packing order. These experimental and theoretical results establish a quantitative framework for understanding defect-mediated crystallization in polymer systems, enabling the predictive synthesis of highly ordered polymers through precise defect engineering.

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