In situ atom transfer radical polymerization of styrene in the presence of nanoporous silica aerogel: Kinetic study and investigation of thermal properties

摘要

Atom transfer radical polymerization (ATRP) of styrene was performed at 110 C in the presence of organically modified silica aerogel. A hydrophobic silica aerogel was prepared by a two-step, acid-base catalyzed sol-gel polymerization of tetraethoxysilane (TEOS) and surface modification by hexamethyldisilazane (HMDS) at the ambient pressure drying (APD) condition. Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption/desorption, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the silica aerogel. Kinetics of styrene ATRP was evaluated in the presence of silica aerogel. Molecular weight and molecular weight distribution were determined by gel permeation chromatography (GPC). There is a critical silica aerogel content that polymerization rate reaches to its lowest level. Thus, the sample with 1 wt% of silica aerogel shows minimum k_(app) with respect to the neat polystyrene. Differential scanning calorimetry (DSC) results reveals that competition between chains mobility and increase of molecular weight by addition of silica aerogel content results in an inconsiderable variation of the T_g value. The nanocomposite with 1 wt% of silica aerogel shows minimum T_g value (81.4 C) respect to near polystyrene (94 C). Transmission electron microscopy (TEM) was used to exhibit the pore size distribution of silica aerogel and either the disappearing of pores by a layer of polystyrene after polymerization.