UV-Curable High-Refractive-Index Resin Based on Polysulfide With Pendant Methacrylate Formed by Selective Cationic Ring-Opening Polymerization of Thiirane

In this paper, we aimed to synthesize polysulfide with pendant methacryloyl groups in the side chain. They are expected to have great potential for various applications as UV-curable higher-refractive-index resins. Thiiran-2-ylmethyl methacrylate (TMA) could be synthesized by the reaction of glycidyl methacrylate with thiourea using conc. H₂SO₄ as a catalyst. Selective ring-opening polymerization of TMA could be achieved using CuCl₂ as an initiator in CHCl₃ at 25°C, yielding the corresponding polysulfide polyTMA_(MA) with pendant methacryloyl groups in the side chain in high yield. The copolymerization of TMA and phenoxypropylene sulfide (PPS) was also performed to give poly(TMA_(MA)m-co-PPS_n) with M _n = 1330–1940 (M _w/M _n = 1.03–2.02) in high yields. The UV-curing reaction of thin films of polyTMA_(MA) and poly(TMA_(MA)m-co-PPS_n) containing a photo-radical initiator proceeded smoothly under UV light, quantitatively affording the corresponding cured thin films. The refractive indices of the thin films before and after UV irradiation were determined by ellipsometry. Among them, poly(TMA_(MA)22-co-PPS₇₈) showed the highest refractive index value (n = 1.763) after the UV-curing reaction.