Activators Regenerated by Electron Transfer for Atom Transfer Radical Polymerization of Styrene in the Presence of Hydrophobically Modified Silica Aerogel Nanoparticles

Abstract

Abstract Pristine hydrophilic silica aerogel nanoparticles surface was functionalized with hexamethyldisilazane (HMDS). Then, the resultant modified nanoparticles were used for in situ polymerization of styrene by activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) to synthesize well-defined polystyrene nanocomposites. Success surface modification of hydrophilic silica aerogel nanoparticles with HMDS is demonstrated by FTIR spectroscopy and TGA. 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. Adding of hydrophobic silica aerogel nanoparticles by 3 wt % results in a decrease of conversion from 89 to 64%. Molecular weight polystyrene chains decreases from 53991 to 42701 g · mol –1 by addition of 3 wt % hydrophobic silica aerogel nanoparticles; however, polydispersity index values increases from 1.22 to 1.6. A peak around 4.15 ppm which originates from hydrogen atom of terminal units of polystyrene chains in proton nuclear magnetic resonance spectra can appropriately demonstrate the living nature of the polymerization. Increasing thermal stability of the nanocomposites is demonstrated by TGA. Differential scanning calorimetry shows a decrease in glass transition temperature from 80.3 to 68.9 ℃ by addition of 3 wt % hydrophobic silica aerogel nanoparticles.