Tensile properties and adhesion of water-absorbing hydrogels based on ternary poly(N-vinyl pyrrolidone)/poly(ethylene glycol)/poly(methacrylic acid-co-ethylacrylate) blends

Rubber-like elasticity and pressure-sensitive adhesion of ternary blends of high-molecular-weight poly(N-vinyl pyrrolidone) (PVP) with oligomeric poly(ethylene glycol) (PEG) of molecular weight 400 g/mol and a co-polymer of methacrylic acid with ethylacrylate (PMAA-co-EA) is due to formation of a interpolymer hydrogen bonded complex. In the ternary blend, PVP is present in a greater amount and acts as a film-forming polymer (FFP). As each short chain of PEG bears two terminal hydroxyl groups, which are capable of forming hydrogen bonds with the carbonyl groups in PVP repeat units, PEG behaves as a reversible carcass-like cross-linker (CLC) between long PVP macromolecules. In addition, the PMAA-co-EA forms a ladder-like interpolymer complex with PVP via hydrogen bonding of carboxyl groups and serves as a ladder-like cross-linker (LLC) of PVP. Adhesion behavior, mechanical properties and water-absorbing capacity of PVP/PEG/PMAA-co-EA blends are functions of blend composition. The CLC (PEG) endows pressure-sensitive adhesion to PVP blends, acting simultaneously as PVP plasticizer, as well as enhancer of cohesive strength. While the PVP/PEG inter-polymer complex is soluble in water, the LLC (PMAA-co-EA) provides insolubility and swellability, increasing further the cohesive strength of the blend composition. At high LLC concentrations, the blends lose their initial tack but become tacky upon water uptake. In this way, ternary PVP/PEG/PMAA-co-EA blends combine tack, typical of conventional hydrophobic pressure-sensitive adhesives, with the capability to adhere to highly hydrated substrates, typical of bioadhesives.