Dissolution dynamics of poly(4-hydroxystyrene) partially protected with t-butoxycarbonyl group in alkyltrimethylammonium hydroxide aqueous developers

Novel developers with low biotoxicity have attracted considerable attention with respect to ensuring environmental sustainability. In this study, the dissolution dynamics of poly(4-hydroxylstyrene) (PHS) partially protected with a t-butoxycarbonyl (t-Boc) group in alkyltrimethylammonium hydroxide and tetraethylammonium hydroxide aqueous solutions (0.26 N) were investigated by the quartz crystal microbalance method. One of the methyl groups of tetramethylammonium hydroxide (TMAH) was substituted by ethyl, propyl, and butyl groups. Depending on the developer used, the dissolution dynamics of PHS and t-Boc-protected PHS (t-Boc PHS) films showed different tendencies. The dissolution rate of PHS was higher in the TMAH developer than in the butyltrimethylammonium hydroxide (B-TMAH) developer, whereas that of the t-Boc PHS (30 mol%-protected) film was higher in the B-TMAH developer than in the TMAH developer. The elongation of one of the alkyl chains is beneficial for the penetration of the developer and the separation of nonpolar molecular interactions among t-Boc PHS molecules.