Hydrogen-bond interaction of PMAA/PVAc blends:: A natural abundant two-dimensional exchange 13C NMR investigation

The natural abundant two-dimensional exchange (CNMR)-C-13 revealed the very close proximity between the carboxyl carbon of PMAA and carbonyl carbon of PVAc in the miscible PMAA/PVAc = 3/1 blend. The estimated distance between the CO carbons is approximately 0.37 nm. This close distance is induced by a strong hydrogen bond between the hydrogen of carboxyl group for PMAA and the oxygen of carbonyl group for PVAc. The molecular mechanics (MM) calculation reveals that the distance of the hydrogen bond between the hydrogen of the carboxyl group and the oxygen of the carbonyl group is approximately 0.2 nm by fixing the intermolecular (inter-polymer) C-C distance between the CO carbons to be 0.37 nm. This value is reasonable for the very strong hydrogen bonding interaction. This interaction makes the C-13 chemical shift value of PVAc carbonyl carbon peak toward lower field by 4 ppm and that of PMAA carboxyl carbon peak to change toward upper field by 4 ppm. The MM calculation also showed that the distance between the backbone carbons of PMAA and PVAc is less than I nm. This very cross proximity for the interacted region is important to create the homogenous PMAA/PVAc blends on a scale of 2-5 nm.