Polystyrene-silica aerogel nanocomposites by in situ simultaneous reverse and normal initiation technique for ATRP

Abstract

Hexamethyldisilazane (HMDS) was employed to surface modification of hydrophilic silica aerogel nanoparticles. Then, the resultant modified nanoparticles were used for in situ polymerization of styrene by simultaneous reverse and normal initiation technique for atom transfer radical polymerization (SR&NI ATRP) to synthesize tailor-made polystyrene nanocomposites. Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) were employed for demonstrating success surface modification of hydrophilic silica aerogel nanoparticles with HMDS. Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the synthesized hydrophobic silica aerogel nanoparticles. Evaluation of size distribution and morphological studies were also performed by SEM and TEM. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography respectively. Addition of 3 wt% hydrophobic silica aerogel nanoparticles results in a decrease of conversion from 97 to 77%. Molecular weight of polystyrene chains decreases from 11095 to 8755 g.mol-1 by addition of 3 wt% hydrophobic silica aerogel nanoparticles; however, polydispersity index (PDI) values increases from 1.15 to 1.46. Appropriate agreement between theoretical and experimental molecular weight in combination with low PDI values demonstrate the living nature of the polymerization. Thermal stability of the neat polystyrene and its different nanocomposites are studied by TGA. Differential scanning calorimetry shows a decrease in glass transition temperature from 94.8 to 83.5 °C by adding 3 wt% of hydrophobic silica aerogel nanoparticles.