A Realizable Green Strategy to Negative Polyurethane Photoresists through the Application of a Silicone Resin Photoinitiator

In order to realize the recycling of negative photoresist materials, four thioxanthone silicone resin photoinitiators (TXSRs) were prepared and used in the preparation of a polyurethane acrylate (PUA) negative photoresist. Their structures were confirmed by 1H NMR, 13C NMR, 29Si NMR, FTIR, and GPC. The photopolymerization kinetics of acrylate monomers initiated by the TXSRs demonstrated their comparative initiating activities to the commercial CQ (camphorquinone)/MDEA (N-methyldiethanolamine) composite. TXSRs are also revealed as a polymer modifier by evidence of the improved properties for the cured films such as better thermal stability, lower surface tension, and enhanced resistance against solvent. Due to their high initiating efficiency and better ethanol resistance of the cured PUA films, a trial pattern experiment of PUA with TXSR-2 as a photoinitiator developed in ethanol was successfully carried out. More importantly, the PUA negative photoresist without light exposure could be recovered and used next time.