Bicyclic Structure–Induced Crystallization Suppression in Bio‐Based Long‐Chain Polyamide Toward Simultaneous Toughening and High Optical Transparency

ABSTRACT Polyamide (PA), as an important engineering plastic, exhibits excellent wear resistance and mechanical properties. However, due to its strong hydrogen bonding interactions and amide groups, it possesses poor light transmittance. To address the issues of poor transparency and insufficient toughness of long‐chain nylon PA612 caused by its high crystallinity, 4,4′‐diaminodicyclohexylmethane (PACM) with bicyclic structure featuring significant steric hindrance was employed to copolymerize long‐chain nylon in this study to prepare PA612‐co‐PACM12 copolymers through molecular structure design. The copolymer structure was characterized by FTIR and 1 HNMR, and its thermal, crystallization, mechanical, rheological, dynamic mechanical, and optical properties were systematically evaluated. The results show that the incorporation of PACM disrupted the regularity of PA612 chains, suppressed crystallization, and reduced crystallinity. At 40% PACM content, the copolymer became fully amorphous, exhibiting high transparency (91.2% at 550 nm). The introduction of the copolymer monomer also achieves toughening effects. Therefore, we successfully obtained a transparent nylon with excellent toughness based on bicyclic structure monomer modified long‐chain nylon PA612. This research achievement not only broadens application scope in fields such as optics and packaging materials, but also provides new research approaches for developing transparent and impact‐resistant functionalities in long‐chain nylon materials.