Composites prepared by penetrating poly(ethylene oxide) chains into mesoporous silica

Mesoporous silica was synthesized by hydrolysis of tetraethylorthosilicate (TEOS, formula Si(OCH₂CH₃)₄) at ambient temperature in a basic ethanol-water solution, with cetyltrimethyl ammonium bromide as a template. It had a surface area of approximately 1,400 m²/g, and an average pore diameter of approximately 40 Å. Portions were blended into three samples of poly(ethylene oxide) (PEO) of varying molecular weights, in the hope of making novel composites by penetrating some of the PEO chains into the silica channels. Differential Scanning Calorimetry (DSC) and X-ray diffraction (XRD) were used to characterize the structures of the PEO/mesoporous silica composites after they were held at 100 °C for up to 30 min. In both experiments, the melting temperature of the PEO decreased and ultimately disappeared. These results suggest that the PEO chains did penetrate into the silica pores, and since they were constrained in the pores, their crystallization was suppressed. This provides an interesting parallel to the disappearance of the glass transition temperatures of polymers constrained in the cavities of zeolites or in the galleries of intercalated clays.