Synthesis of a branched photosensitive copolymer and its application for negative-type photoresists

Novel branched copolymers, poly(styrene- alt -maleic anhydride) (BPSMA), were synthesized through mercapto chain-transfer polymerization with styrene, maleic anhydride (MA), and 4-vinyl benzyl thiol (VBT). Then, the hydroxyl of hydroxyethyl methacrylate was reacted with MA to synthesize branched photosensitive copolymers, p -BPSMAs. Fourier transform IR spectroscopy and 1 H-NMR indicated that the synthesis was successful. Gel permeation chromatography indicated that the molecular weight decreased with increasing content of VBT. The thermal properties were characterized by thermogravimetric analysis; the results show that the thermal decomposition temperature of the BPSMAs was greatly enhanced. Real-time IR was used to evaluate the UV-curable kinetics of the p -BPSMAs; the results show that the p -BPSMAs could rapidly photopolymerize under UV irradiation in the presence of photoinitiators. Moreover, the photoresist based on the p -BPSMAs exhibited improved photosensitivity when the VBT content increased, and the photoresist with 12 mol % VBT content had a low value of the dose that retained 50% of the original film thickness (10 mJ/cm 2 ), and a 50-μm resolution could be achieved compared to a linear photoresist. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 42838.