Determination of the sequence distribution and ionization constant of poly(acrylic acid-co-vinylamine) by C-13 NMR

Three copolymers of poly(acrylic acid-co-vinylamine) containing 12% (SP12). 30% (SP30), and 52% (SP52) amino groups were synthesized from poly(acrylic acid) by means of the Schmidt reaction. These copolymers were analyzed by C-13 NMR and the results compared wiih the previously analyzed homopolymers. The various comonomer sequence distributions were identified by means of peak areas. It was determined thai (1) the reactivity was not significantly influenced by the triad taciicity of the parent poly(acrylic acid), (2) the final copolymer is characterized by an essentially alternating sequence, and (3) there is extensive lactam formation between neighboring carboxyl and amino groups. In terms of nearest neighbor effects, the relative rales of amine formation are k₁/k₀ ≈ 0.3 and k₂/k₀ ≈ 0. A C-13 NMR pH titration of SPI2 showed that the carboxyl group with a neighboring amino group is more acidic man a carboxyl group flanked by two carboxyl groups.