Competitive hydrogen bonding mechanisms underlying phase behavior of triple poly(N-vinyl pyrrolidone)-poly(ethylene glycol)-poly(methacrylic acid-co-ethylacrylate) blends

Differential scanning calorimetry (DSC) of triple blends of high molecular weight poly(N-vinyl pyrrolidone) (PVP) with oligomeric poly(ethylene glycol) (PEG) of molecular weight 400 g/mol and copolymer of methacrylic acid with ethylacrylate (PMAA-co-EA) demonstrates partial miscibility of polymer components, which is due to formation of interpolymer hydrogen bonds (reversible crosslinking). Because both PVP and PMAA-co-EA are amorphous polymers and PEG exhibits crystalline phase, the DSC examination is informative on the phase state of PEG in the triple blends and reveals a strong competition between PEG and PMAA-co-EA for interaction with PVP. The hydrogen bonding in the triple PVP-PEG-PMAA-co-EA blends has been established with FTIR Spectroscopy. To evaluate the relative strengths of hydrogen bonded complexes in PVP-PEG-PMAA-co-EA blends, quantum-chemical calculations were performed. According to this analysis, the energy of H-bonding has been found to diminish in the order: PVP-PMAA-co-EA-PEG(OH) > PVP-(OH)PEG(OH)-PVP > PVP-H2O > PVP-PEG(OH) > PMAA-co-EA-PEG(-O-) > PVP-PMAA-co-EA > PMAA-co-EA-PEG(OH). Thus, most stable complexes are the triple PVP-PMAA-co-EA-PEG(OH) complex and the complex wherein comparatively short PEG chains form simultaneously two hydrogen bonds to PVP carbonyl groups through both terminal OH-groups, acting as H-bonding crosslinks between longer PVP backbones. (C) 2007 Wiley Periodicals, Inc.