Photohydrolysis of substituted benzyl esters in multilayered polyelectrolyte films

Poly(acrylic acid) (PAA) is partially esterified with various benzyl (i.e., benzyl, 3-methoxy-benzyl, 3,5-dimethoxybenzyl, and 2-nitrobenzyl) groups, and the resulting benzyl acrylate copolymers are then incorporated into multilayered polyelectrolyte films. Upon exposure to UV light, the benzyl groups are photohydrolyzed. The hydrolysis is monitored by reflectance FTIR spectroscopy, ellipsometry, and advancing water contact angle measurements. The nature of the substituents on the aromatic rings affects the photoreactivity and thermal stability of the films. For example, 3,5-dimethoxybenzyl and 2-nitrobenzyl esters are photohydrolyzed to form primarily acid groups in the film matrix. On the other hand, when benzyl and 3-methoxybenzyl ester films are irradiated, fewer acid groups are formed. Films made with 3,5-dimethoxybenzyl groups appear to be the most thermally stable during the cross-linking of the polymeric film layers.