A comprehensive study of the bicontinuous epoxy-silica hybrid polymers: I. Synthesis, characterization and glass transition

This paper presents a novel two-stage chronological procedure developed for the synthesis of bicontinuous epoxy-silica hybrid polymers. The epoxy-silica polymers are produced by solvent-free hydrolysis of tetraethylorthosilicate into the liquid epoxy resin, followed by the crosslinking of epoxide groups with a diamine curing agent. The two types of bicontinuous epoxy-silica hybrid polymers prepared in this way contain 0-30 wt.% silica and differ only in the absence or presence of (3-glycidoxypropyl)trimethoxysilane (GLYMO); minimal amount of which is used for the in situ functionalization of silica. GCMS and DSC analyses provide an insight into the reaction mechanism, and reveal that total conversion of silanes as well as epoxy groups is feasible in this way. The free-standing epoxy-silica polymer films are subsequently characterized by the attenuated total reflectance FTIR spectroscopy and AFM. The AFM micrographs exhibit a very fine dispersion of nanoscale silica into the organic matrix that is further enhanced on addition of GLYMO. The presence of GLYMO substantially affects the particle size and distribution, augments the adhesion of the two phases, and inhibits the macroscopic phase separation. The glass transition temperatures of epoxy-silica polymers are also improved by 20.4%; which is attributed to the formation of entangled epoxy-silica networks.