Thermal degradation of poly(methyl methacrylate) on SiO 2 nanoparticles as a function of SiO 2 size and silanol density

Abstract

The degradation behavior of amorphous polymethyl methacrylate (PMMA) on silica (SiO 2) nanoparticles (PMMA–SiO 2) as a function of silanol density and nanoparticle size was investigated by derivative thermogravimetric analysis (dTGA). The thermal degradation temperature, T d, was measured for PMMA adsorption amounts below plateau adsorption, which enhanced the contribution of chains in direct contact with the silica. T d increased as the number of hydrogen bonds between the silanol (SiOH) groups of the SiO 2 and the carbonyl (C O) of the PMMA increased, either from varying the heat treatment of the SiO 2, which changed the silanol density, or increasing the nanoparticle size, thus increasing the number of sites where the PMMA chain contacted the nanoparticles. The increases in T d correlated with increases in T g for the PMMA–SiO 2, suggesting that the enhanced thermal stability was attributable to decreased segmental mobility of PMMA chain segments, which in turn decreased thermally induced degradation. T d and T g did not change for polar PMMA on hydrophobically modified SiO 2, (CH 3)–SiO 2, as expected based on this mechanism, since there were no specific hydrogen-bond interactions between the C O of PMMA and the Si–O–(CH 3) 3 of SiO 2.