A thin-film calorimeter (TFC) was used to provide quantitative characterization of photopolymerizable systems. Photopolymerization exotherms measured using the TFC are compared with real-time infrared (RTIR) spectroscopic results. The TFC successfully monitored the in-situ polymerization kinetics of thin/thick films because of its increased sensitivity/resolution over traditional calorimetric instrumentation. Reproducible polymerization exotherms of trimethylolpropane triacrylate were measured on films as thin as 163 nm. Flexibility in the sample cell construction enables the characterization of both volatile reactants (closed cell) and the effect of oxygen inhibition (open cell). Several molecular systems were evaluated. First, exotherms for the reaction of a series of volatile hexene monomers with monofunctional thiol illustrate the effect of ene location on alkene reactivity. Second, vinyl acrylate, a volatile difunctional monomer with a unique polymerization mechanism, was shown to homopolymerize significantly faster than either of its monofunctional analogues. Additionally, the rapid instrument response time of the TFC allowed qualitative analysis of non-steady-state polymerization kinetics of vinyl acrylate.