Visualization of Polymer Chain Alignment in Fiber Spinning and Hot Stretching by Noncovalent Polymer Mechanochemistry

Polymer chain orientation and microstructures are crucial to achieving high performance in fibers. However, in situ detection and further control of these polymer-condensed matter structures during fibrous processing are challenging due to the high velocity of spinning and the small size of fibers. Here, we report a visual approach for monitoring polymer microstructures and chain alignment in fibers by the mechanically induced fluorescent color change of perylene diimide (PDI) mechanophores. PDI derivatives with different solubilities were synthesized and used to prepare solutions with distinct fluorescence colors, arising from varying degrees and packing of aggregation. The mechanism of distinct fluorescence further guided the synthesis of mechanoresponsive polyurethanes by embedding various contents of PDI along the polyurethane backbone. The resulting polyurethanes exhibited obvious fluorescence color change during deformation owing to the dissociation of PDI stacking, enabling real-time monitoring of microstructures in fiber processing. A fluorescent color change from red to green was observed during hot stretching, indicating the associated orientation of the polymer chains and crystalline formation. These microstructural changes, analyzed by WAXD, are quantitatively reflected in the reinforcement of fiber mechanical properties. Accordingly, the relationship between fluorescent color and fiber strength or modulus was established to enable the in situ visual detection of fiber mechanical properties during spinning. The unique mechanoresponsive mechanism of PDI mechanophores points to a novel application of noncovalent polymer mechanochemistry in the field of fiber technology.