Polymerization exotherms of 1,6-hexanediol diacrylate (HDDA) were generated by a pulsed laser source and recorded on a modified differential scanning calorimeter. Several aromatic carbonyl-based photoinitiators were compared with respect to maximum rate and extent of polymerization in the absence and presence of oxygen. α-Cleavage photoinitiators were more efficient than the hydrogen-abstracting benzophenone. The addition of an amine to a photocleavable initiator improved the polymerization of HDDA under an inert atmosphere, whereas triarylphosphines under similar conditions were effective in reducing the air inhibition. This synergistic effect depends on the type and structure of the additive and the photoinitiator.