Frontal free-radical copolymerization of urethane-acrylates

We report the first synthesis of urethane-acrylate copolymers via free-radical frontal polymerization. In a typical run, the appropriate amounts of the reactants (urethane-acrylate macromonomer and 2-hydroxyethyl acrylate) and initiator (ammonium persulfate) were dissolved in dimethyl sulfoxide. Frontal polymerization was initiated by the heating of the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self-propagate throughout the reaction vessel. Once it was initiated, no further energy was required for the polymerization to occur. The dependence of the front velocity and front temperature on the initiator concentration was investigated. The front temperatures were between 55 and 65°C, depending on the persulfate concentration. Thermogravimetric analysis indicated that the urethane-acrylate copolymers had higher thermal stability than pure frontally prepared polyuretnane.