Percolation of glassy regions during photopolymerization of epoxy acrylate in DMF

The gelation of epoxy acrylate (EA) 80% and tripropyleneglycol diacrylate (TPGDA) 20% was studied through the use of photo-differential scanning calorimetric (photo-DSC) technique in the presence of a thioxanthone based initiator. Photo-induced polymerization reactions were performed under identical conditions of temperature, initiator concentration and UV light intensity in various N,N-dimethylformamide (DMF) contents. Photo-DSC technique allowed us to monitor the gelation without disturbing the system mechanically, and to test the universality of the gelation as a function of DMF content. During gelation, it was observed that all conversion curves presented useful sigmoidal behavior which was predicted by employing a percolation model. Observations around the glass transition point, t(g), revealed that gel fraction exponent beta obeyed the percolation picture. A significant solvent effect on the photopolymerization kinetics of EA/TPGDA was observed with changes in DMF content. DMF is used as solvent, which acts as a diluent and proton donor during photogelation. (C) 2014 Elsevier B.V. All rights reserved.