Epoxy/polyhedral oligomeric silsesquioxane (POSS) hybrid networks cured with an anhydride: Cure kinetics and thermal properties

A new class of organic-inorganic hybrid networks was prepared via copolymerization of octakis(dimethylsiloxybutyl epoxide)octasilsesquioxane (OB), N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) and hexahydrophthalic anhydride (HHPA). Kinetic studies show that even with 1H-imidazole as the catalyst, the rate for the curing of OB/HHPA is still significantly higher than that for TGDDM/HHPA in the temperature range studied. Two-stage reactions were thus carried out to allow OB to react with HHPA first (Stage I). The glass transition temperature (T_g) of the networks was found to be strongly dependent on Stage I reaction since too short a reaction time caused poor bonding of OB to the networks while too long a reaction time led to the formation of OB oligomers that de-homogenized the networks. With 5 mol.% OB, the hybrid prepared via the optimized two-stage reaction displayed a large jump of ∼20 °C in T_g, which was accompanied by slight improvements in thermal degradation temperature and storage modulus, as compared to TGDDM/HHPA.