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 ¹H‐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/cm²), and a 50‐μm resolution could be achieved compared to a linear photoresist. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42838.