Free-radical crosslinking copolymerization of styrene/unsaturated polyester resins: 1. Phase separation and microgel formation

An important feature of free-radical crosslinking copolymerization of styrene (ST)/unsaturated polyester (UPE) resins is the formation of a heterogeneous structure through strong intramolecular reactions and phase separation. Such structure formation affects not only the cure behaviour and rheological changes of the resin but also the physical properties of final products. In this study, the phase separation process was investigated by optical microscopy and time-resolved light scattering goniometry. Partially reacted samples of ST/UPE resin before macrogelation were also prepared by stopping the polymerization at preset times. The size and composition of primary polymers were determined using dynamic light scattering goniometry and Fourier transform infra-red spectroscopy.