Synthesis and characterization of poly(N-vinyl formamide) hydrogels - A potential alternative to polyacrylamide hydrogels

The synthesis and characterization of solution-cast, molded gels of N-vinyl formamide (NVF) has not been previously reported even though NVF is an isomer of acrylamide (AAm) and polyacrylamide (PAAm) hydrogels have many commercial applications. Aqueous NVF solutions were cross-linked into gels using a novel cross-linker, 2-(N-vinylformamido)ethylether, and the thermally-activated initiator VA-044. For a given formulation, PNVF gels swell up to twice that of PAAm gels cross-linked with N,N′-methylenebisacrylamide. From swelling and compression measurements, PNVF gels were found to be more hydrophilic than PAAm gels. Flory-Huggins solubility parameters were χ = 0.38ph₂ + 0.48 for PNVF and χ = 0.31ph₂ + 0.49 for PAAm, where ph ₂ is the polymer volume fraction. The shear moduli for PNVF and PAAm scale with ph 22.0 and ph 22.5 respectively, consistent with good solvent behavior, also suggesting PNVF is more hydrophilic than PAAm. Similarity of mechanical properties for both gels as a function of ph₂ suggests that network structures of PNVF and PAAm gels are similar. Fracture strains of both gels declined with ph₂ by the same linear function while fracture stresses were about 500 kPa regardless of formulation. Since NVF is a liquid monomer, less toxic than AAm and can be hydrolyzed to a cationic form, PNVF gels could become technologically significant.