Hybrid dual-cure polymer networks via sequential thiol-ene photopolymerization and thermal ring-opening polymerization of benzoxazines

Dual-cure hybrid polymer networks were prepared by sequential thiol-ene photopolymerization followed by thermal ring-opening polymerization of benzoxazines with the aim of increasing the glass transition temperature range of thiol-ene based materials and improving the processibility of polybenzoxazines. The hybrid networks are derived from a multifunctional, dually-polymerizable monomer possessing both bis-“ene” and bis-benzoxazine moieties enabling the formation of two networks through a common constituent monomer when combined with a multifunctional thiol. The photopolymerization kinetics of the thiol-ene reaction were investigated by real-time infrared spectroscopy. Sequential thermal ring-opening polymerization of the benzoxazine moieties incorporated into the thiol-ene network was characterized by FTIR and differential scanning calorimetry. The glass transition of the hybrid material was observed at 150 °C; however, competing thiol-ene (radical-mediated) and thiol-benzoxazine (nucleophilic ring-opening) reactions during the UV cure yield a heterogeneous network structure.