Copolymers from tert‐Butyl Methacrylate with Trimethylsilyl Methacrylate or Methacrylic Acid: Models for Resist Polymers

Abstract Free radical copolymerisation of tert ‐butyl methacrylate ( 1 ) with trimethylsilyl methacrylate ( 2 ) and methacrylic acid ( 3 ) has been investigated. Reactivity ratios for methacrylic acid and tert ‐butyl methacrylate indicate an azeotropic copolymerisation (r 1 = 0.476 ± 0.103; r 3 = 0.300 ± 0.032), whereas the two esters show preferential incorporation of 2 (r 1 = 0.170 ± 0.050; r 2 = 1.170 ± 0.124). Thermal cis ‐elimination of isobutylene from the tert ‐butyl ester and subsequent formation of six‐membered cyclic anhydride moieties has been studied. For poly(methacrylic acid‐ co ‐ tert‐ butyl methacrylate) thermogravimetry could be used to determine copolymer composition. Solvolytic desilylation of the trimethylsilyl ester groups has been investigated as an alternative route to poly(methacrylic acid‐ co ‐ tert ‐butyl methacrylate). The tert ‐butyl ester is not affected under the conditions of desilylation. Sequence distribution of both copolymers has been calculated using the method introduced by Bruns and Motoc. Copolymer composition diagram for tert ‐butyl methacrylate/methacrylic acid. image Copolymer composition diagram for tert ‐butyl methacrylate/methacrylic acid.