INTERPOLYMER COMPLEXATION OF POLY(ACRYLIC ACID) AND POLY(ACRYLAMIDE) - STRUCTURAL AND DYNAMIC STUDIES BY SOLUTION- AND SOLID-STATE NMR

Interpolymeric complexes of poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) at 60, 20, 5, and 0% ionization (alpha) were studied by H-1/C-13 solution-state and C-13 solid-state cross-polarization magic angle spinning (CPMAS) NMR experiments. The solid-state NMR results support a model in which ionization (alpha or pD) alteration leads to conformation and segment changes along the PAA-PAAm polymeric backbone. Solid-state relaxation measurements show short T-1 values at high ionization (alpha = 60%) but long T-1 values toward low ionization (alpha less than or equal to 20%). This is consistent with a model in which the PAA and PAAm polymers take on a stretched but mobile conformation at high ionization but become immobile and restricted at low ionization. Dynamic restriction of the polymer is attributed to symbiotic hydrogen bonding of the carboxyl group of PAA and the amide residue of PAAm to form interpolymer complexes. Other relaxation parameters such as H-1-C-13 cross-polarization times T-CH(SL), proton spin-lattice relaxation times in the rotating frame T-1 rho(H), and C-13 dipolar-dephasing results are also consistent with this model.