Hybrid polyurethane acrylate films via thiol–ene click and sol–gel reactions: Monomer-dependent structure–property relationships

This study introduces a novel strategy for enhancing UV-curable polyurethane acrylate (PUA) coatings by integrating thiol–ene click chemistry with sol–gel processing. Hybrid polyurethane acrylate (HPUA) films were synthesized using biuret-type hexamethylene diisocyanate (HDI) and a pentaerythritol (PENTA) core, followed by end-capping with three structurally distinct acrylate monomers: 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate (HEA), and 2-hydroxypropyl methacrylate (HPMA). Subsequently, (3-mercaptopropyl)trimethoxysilane (MPTMS) was grafted onto the acrylate-terminated polymers via a thiol–ene click reaction under UV irradiation to introduce alkoxysilane groups for sol–gel hybridization. The objective was to investigate how monomer architecture influences the development of organic–inorganic networks and the resulting thermal, mechanical, and surface properties. FTIR spectral deconvolution confirmed enhanced hydrogen bonding and crosslinking, especially in HPMA-based systems. DSC and TGA results showed that HPMA–HPUA exhibited the highest glass transition temperature (T_g from −13.52 °C to 90.0 °C) and thermal stability (T₅₀ from 380 °C to 457 °C), attributed to improved interfacial compatibility with the silica network. Surface analyses revealed increased hardness and hydrophobicity after sol–gel modification, with contact angles rising up to 130°. This study establishes a clear structure–property relationship framework for monomer-dependent hybridization and presents a scalable approach for designing high-performance, UV-curable coatings with customizable thermal and mechanical properties.