Influence of surface modified TiO _2 nanoparticles by gallates on the properties of PMMA/TiO _2 nanocomposites

摘要

Nanocomposites based on poly(methyl methacrylate) (PMMA) and TiO _2 nanoparticles were synthesized by in situ radical polymerization of MMA in solution. The surface of TiO _2 nanoparticles was modified with four gallic acid esters (octyl, decyl, lauryl and cetyl gallate). The content of gallates present on the surface of TiO _2 was calculated from the TGA results. The influence of length of hydrophobic tail of amphiphilic alkyl gallates on dispersability of surface modified TiO _2 nanoparticles in PMMA matrix, the molecular weight and glass transition temperature of PMMA, as well as the thermal stability of the prepared PMMA/TiO _2 nanocomposites in nitrogen and air was investigated. The influence of content of TiO _2 nanoparticles on the properties of these nanocomposites was also examined. The formation of a charge transfer complex between the surface Ti atoms and the gallates was confirmed by FTIR and UV spectroscopy. TEM micrographs of the PMMA/TiO _2 nanocomposites revealed that degree of TiO _2 aggregation can be significantly lowered by increasing the length of aliphatic part of the used gallates. The molecular weight of PMMA slightly decreases with the increase of TiO _2 content, indicating that used TiO _2 nanoparticles act as radical scavengers during the polymerization of MMA. The presence of surface modified TiO _2 nanoparticles do not have an influence on the mobility of PMMA chain segments leading to the same values of glass transition temperature for all investigated samples. Thermal and thermo-oxidative stability of the PMMA matrix are improved by introducing TiO _2 nanoparticles modified with gallates.