Interpolymer complexation. I. Preparation and characterization of a polyvinyl acetate phthalate-polyvinylpyrrolidone (PVAP-PVP) complex.

Polyvinyl acetate phthalate (PVAP) and polyvinylpyrrolidone (PVP) readily reacted in ethanol and acidic aqueous solutions to produce an insoluble PVAP-PVP complex. The complex has a pK(a) of 3.8. It is practically insoluble in common organic solvents, but dissolves in dimethylsulfoxide, an alkali or ammonical solution, and a 4:1 (v/v) mixture of methylene chloride and methanol. The powder X-ray diffraction analysis revealed the complex to be an amorphous material. The Fourier-transform infrared spectrum of the complex exhibited characteristics carbonyl stretching vibrations at 1724 and 1657 cm(-1) due to phthalate and acetate moieties in PVAP and cyclic amide groups in PVP, respectively, and at 1632 cm(-1) (appeared as a shoulder) due to cyclic amide groups of PVP bound to PVAP. The proton and carbon-13 (solution and solid-state) nuclear magnetic resonance spectra of the complex showed peak profiles that were linear combinations of those of PVAP and PVP. No new peaks appeared and no change in chemical shifts was observed due to complexation. The spectral data suggest that the interaction between PVAP and PVP probably initially involves the formation of hydrogen bonds between carbonyl groups of PVP and carboxylic groups of PVAP at some point of the polymer chains, causing the hydrophilic parts of the two flexible polymer chains strongly hydrophobic. As a result, the two polymer chains coil up into a compact structure and, consequently, precipitate out from the solution as an insoluble complex.