Cationic Photocuring of Vinyl Ether Polyurethanes toward Resilient and Transparent Optical Adhesives

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Conventional radical-based UV-curable acrylic pressure-sensitive adhesives (PSAs) are severely limited by oxygen inhibition, leading to incomplete surface curing and polymerization shrinkage. To address these issues, we report a cationic photopolymerization strategy based on vinyl ether-functionalized polyurethanes for fabricating high-performance optically clear PSAs. A vinyl ether-terminated prepolymer (PUE-BDO) was synthesized by the chain extension of an isocyanate-terminated polyurethane with 1,4-butanediol, followed by end-capping with 4-hydroxybutyl vinyl ether (HBVE). A difunctional vinyl ether monomer (IP-VE) was prepared from HBVE and isophorone diisocyanate. By systematically adjusting the ratios of PUE-BDO, IP-VE, and triethylene glycol divinyl ether (DVE-3), we achieved precise control over the cross-linking network and viscoelastic properties of the materials. The resulting PSAs exhibited exceptional optical clarity, with 99% transmittance and <0.3% haze, alongside rapid strain recovery (<1 s) and a high creep-recovery ratio (∼90%) after 100 loading–unloading cycles at 20% strain. At an optimal composition (50 wt % prepolymer), the PSA demonstrated a 180° peel strength of 18.2 N/25 mm and a loop tack of 17.3 N/25 mm. This study presents a robust and tunable cationic photocuring platform for next-generation flexible display encapsulation that is free from oxygen inhibition and capable of meeting demanding optical and mechanical requirements.