First solvent-free synthesis of poly(N-methylolacrylamide) via frontal free-radical polymerization

We report the first synthesis of poly (N-methylolacrylamide) (PNMA) via free-radical frontal polymerization (FP) with solid monomers at ambient pressure. The appropriate amounts of reactants (N-methylolacrylamide) (NMA) and initiator (ammonium persulfate) were mixed together at ambient temperature without solvent. FP 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. We also produced PNMA with dimethyl sulfoxide (DMSO) or N-methyl-2-pyrrolidone, as solvent by FP, to study the macrokinetics in FP of PNMA without fillers. The front velocity and front temperature dependence on the ammonium persulfate and N-methyl-2-pyrrolidone concentration were investigated. The polymer was analyzed by thermogravimetric analysis. Results show that without postpolymerization solvent removal, waste production can be reduced. Solvent-free FP could be exploited as a means for preparation of PNMA with the potential advantage of higher throughput than solventbased methods.