Effect of tetrahydrofuran on poly(methyl methacrylate) and silica in the interfacial regions of polymer nanocomposites

Abstract

The effects of tetrahydrofuran (THF) on the physical properties of poly(methyl methacrylate) at (PMMA)/silica nanoparticle interfaces in polymer nanocomposites were investigated via differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analysis. Amorphous structures containing PMMA chains with large numbers of trans-gauche conformers were observed in the annealed samples. The amorphous structures in the samples cast from THF suspensions contained PMMA chains rich in trans–trans conformers. These amorphous structures differed from those of neat PMMA prepared without silica. Although the polymer chain mobility was reduced due to interactions between PMMA and the silica nanoparticles, trans–trans-enriched PMMA chains within the amorphous structures were less affected by these interactions. When the amorphous structures were heated above the glass transition temperature of PMMA, the proportion of trans–gauche conformers increased. When the neat PMMA samples were dried at room temperature, the glass transition temperature (Tg) increases linearly with the decrease in the amount of residual solvent. However, even if the residual solvent is extrapolated to 0 wt%, the Tg is significantly lower than the bulk Tg despite no residual solvent. The Tg of heat-dried samples heat treated at 120 °C also increases linearly with decreasing residual solvent content. However, Tg was significantly different depending on the drying temperature even with the same residual solvent amount. These results indicated that the PMMA samples dried at room temperature have a distinctly different molecular mobility from the heated sample.