Observations of gelation and vitrification of a thermosetting resin during the evolution of polymerization shrinkage

We report a new methodology to determine the gelation and vitrification of a thermosetting material during the polymerization process by detecting the evolution of cure shrinkage through a thermomechanical analyzer (TMA) and a differential scanning calorimeter (DSC). The gelation and vitrification determined by the evolution of cure shrinkage correspond favorably with that measured by conventional rheological techniques. The isoconversional phenomenon at gelation point was further confirmed by monitoring cure shrinkage at temperatures ranging from 90 to 110°C. Where-as, vitrification was observed to occur at higher degrees of cure with increasing cure temperatures. Inhibited cure shrinkage was also observed in the vitrification region where the reaction transitioned from chemical to diffusion controlled.