Model experiments have been used to study the cross-linking reactions that are operative in a new negative-tone resist system based on photoacid-catalyzed electrophilic aromatic substitution of copolymers containing benzyl acetate pendant groups. NMR monitoring of the formation of diphenylmethane units in the acid-catalyzed reaction of various benzyl acetates with themselves and with activated aromatic compounds such as 4-isopropylphenol gave insight into the cross-linking reaction. The influence of the leaving group, stabilizing substituents, and nucleophile on the overall process and the possible formation of O-alkylated products or intermediates were studied. © 1991, American Chemical Society. All rights reserved.