Durable silane-based hybrid coating with covalently bonded UV absorber for outdoor optical protection

Abstract

Transparent polymers face a fundamental challenge in outdoor applications: achieving simultaneous optical clarity and UV protection without compromising long-term durability. Conventional UV absorbers suffer from migration, volatilization, and photodegradation, leading to progressive loss of protective functionality. This study presents a novel approach using covalently-integrated UV absorbers in silane-based sol-gel hybrid coatings for transparent polycarbonate protection. A reactive triethoxysilyl-terminated benzophenone UV absorber (TES-BP) was synthesized via platinum-catalyzed hydrosilylation and chemically integrated into silane-based hard coating (HC) formulations. The molecular design ensures covalent anchoring within the siloxane network to effectively maintain the UV-absorbing functionality. Comprehensive characterization under accelerated weathering conditions (1100 h xenon arc exposure) revealed remarkable protective performance. While uncoated polycarbonate exhibited severe yellowing (yellowness index of 5.2) and the base HC failed due to delamination, silane-based covalent hybrid coating (SC-HC) demonstrated significantly enhanced durability and photoprotection ability with concentration-dependency. Optimal performance was achieved at 16 wt. % loading, providing over 90% reduction in yellowing, maintained optical transmittance (90%), preserved surface hydrophobicity (contact angle ~ 90°), and excellent abrasion resistance throughout aging. UV–visible spectroscopy confirmed stable UV screening without spectral degradation, validating the chemical stability of the covalently-bound system. The identification of a performance plateau at 12 ~ 16 wt. % loading provides clear guidelines for cost-effective formulation optimization. This reactive UV absorber strategy successfully addresses the long-standing migration problem while achieving simultaneous optical clarity and photostability, offering significant potential for demanding applications in photovoltaics, automotive, and architectural industries.