Molecularly Designed PFAS-Free Flexible Transparent Films with High UV Stability and 1,000,000-Cycle Folding Reliability

The growing transition toward PFAS-free materials has increased the demand for non-fluorinated optical polymers that can simultaneously provide high transparency, mechanical robustness, and long-term flexibility for next-generation displays and electronic devices. This is particularly important because fluorinated polyimides are currently regarded as the leading class of flexible optical film materials from both academic and commercial perspectives. However, achieving this combination in PFAS-free films remains challenging because replacing fluorinated molecular design motifs requires simultaneous control over charge-transfer complex formation, interchain interactions, and polymer-chain packing. In this study, we developed PFAS-free flexible transparent films through a molecular design strategy based on non-fluorinated functional monomer selection, controlled charge-transfer complex formation, and regulated packing of rigid, non-linear polymer chains. This molecular architecture was designed to minimize optical coloration and light scattering while maintaining cohesive interchain interactions required for mechanically reliable flexible films. The resulting film exhibited a total transmittance above 88%, haze below 0.3%, and a yellowness index below 1.3, demonstrating high optical clarity with minimal coloration. It also showed negligible yellowing after 72 h of UV-B irradiation, indicating high resistance to photo-induced optical degradation. Moreover, it withstood over 1,000,000 folding/unfolding cycles at a bending radius of 1.5 mm without cracking or crease formation, confirming long-term folding reliability under repeated deformation. These results demonstrate that simultaneous control of charge-transfer interactions, backbone rigidity, interchain cohesion, and chain packing provides an effective molecular design strategy for realizing high-performance PFAS-free films for flexible displays and electronics.