Bubble‐Free Frontal Polymerization of Acrylates Using 1,1,2,2‐Tetraphenyl‐1,2‐Ethanediol as a Free‐Radical Initiator

ABSTRACT We demonstrated that using 1,1,2,2‐tetraphenylethanediol (TPED) as the free‐radical initiator in the thermal frontal polymerization of acrylates produced samples without voids, as occurs with peroxide initiators, but with velocities ten times slower than most peroxides. Unlike persulfate initiators, which also produce void‐free materials, TPED is commercially available and allows very long shelf lives. TPED has been used for the radical‐induced cationic frontal polymerization of epoxies but has not been studied with acrylates alone. We investigated the frontal polymerization of various acrylate monomers with TPED at room temperature, including trimethylolpropane triacrylate (TMPTA), a 1:1 mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (PETIA), pentaerythritol triacrylate (PETA), 1,6‐hexanediol diacrylate (HDDA), 1,4‐butanediol diacrylate (BDDA), and diethylene glycol diacrylate (DEGDA). The results were compared to the same monomer systems with the conventional peroxide initiator, Luperox 231, assessing differences in front behavior, shelf‐life, and bubble formation. We also studied the front velocity dependence on TPED concentration and the concentration of the inhibitor 4‐methoxyphenol (MeHQ). The front velocity did not exceed 2 cm/min up to the solubility limit of TPED. The front velocity was significantly reduced by concentrations greater than 1 part per hundred resin (1 PHR).