High Optical Transparency in the Alicyclic Poly(Ether‐b‐amide) Copolymer Induced by Multiscale Structure via Weak Microphase Separation

Developing transparent materials combining superior optical and mechanical properties with robust service stability remains a significant challenge. Herein, an amorphous alicyclic poly(ether-b-amide) (PEBA) copolymer is synthesized by incorporating bis(4-aminocyclohexyl) methane (PACM) into the hard segment (HS) to suppress crystallization, combined with low-molecular-weight poly(tetramethylene ether glycol) (PTMEG) as the soft segment (SS) to enhance segmental compatibility. Such molecular design results in a weakly microphase-separated structure with diffused boundaries between the nanometer microdomains. This "interface-erasing" strategy yields a hot-pressed film with a miscible-dominated morphology with phase regions ranging from 50 to 100 nm, significantly smaller than visible-light wavelengths. Finite element analysis (FEA) simulations further demonstrate that these small phase regions, together with the miscible phase acting as a refractive index (RI) buffer, collectively reduce off-axis scattering, achieving excellent optical clarity (91.1% transmittance, 5.80% haze). The material also shows robust mechanical properties (>30 MPa, >1000% elongation), low-temperature impact resistance, service reliability, solvent resistance, and damping performance. By integrating multiscale characterization and theoretical modeling, this work provides a simple yet effective molecular design strategy and a multiscale mechanistic insight for transparent high performance elastomers, promising for applications as transparent protective layers.