Alkaline hydrolysis of homopolymers and copolymers of 2-hydroxypropyl methacrylate

Homopolymers of 2-hydroxypropyl methacrylate (HPMA) and copolymers with acrylic acid (AA) were prepared in 1,4-dioxane. The reactivity ratios were determined to be r_AA = 0.27 ± 0.04 and r_HPMA = 2.2 ± 0.2. The alkaline hydrolysis by sodium hydroxide of the HPMA monomer and polymers showed that while the HPMA monomer hydrolyzed readily as expected for a low-molecular-weight carboxylic ester the HPMA homopolymer and water-soluble sodium acrylate (NaA) copolymers were extremely resistant to alkaline hydrolysis. The saponification reaction followed a second-order rate equation, being first order with respect to both HPMA and hydroxide ion concentration. The Arrhenius parameters, activation energy E and frequency factor A, for the alkaline hydrolysis of HPMA monomer in water were found to be E = 10.3 Kcal/mol and A = 1.5 × 10⁸ L/mol min, and those for the NaA–HPMA copolymers in water were found to be E = 24 kcal/mol and A = 4 × 10¹² L/mol min. The NaA–HPMA copolymers had a limiting extent of hydrolysis, ranging from 9–90% ester conversion. A sharp rate decrease at low conversion was noted during the HPMA homopolymer hydrolysis in 58/42 dimethyl sulfoxide/water, allowing the calculation of two distinct reaction rates. © 1992 John Wiley & Sons, Inc.