Solvent-free free-radical frontal polymerization: A new approach to quickly synthesize poly(N-vinylpyrrolidone)

The first synthesis of poly(N-vinylpyrrolidone) without solvent by free-radical frontal polymerization at ambient pressure is reported. The appropriate amounts of two reactants N-vinyl-2-pyrrolidone (NVP) and initiator 2,2′-azobis-isobutyronitrile (AIBN) without solvent were mixed together at ambient temperature. Frontal polymerization was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self-propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. To suppress the fingers of molten monomer, a small amount of nanosilica was added. The dependence of the front velocity and front temperature on the AIBN concentration was thoroughly investigated. The as-prepared polymers were characterized by gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). Results show that without postpolymerization solvent removal, waste production can be reduced. Solvent-free FP could be exploited as a means for preparation of PVP with the potential advantage of higher throughput than solvent-based methods.