Thermal, physical and chemical stability of porous polystyrene-type beads with different degrees of crosslinking

The thermal properties of porous polystyrene-type beads with different degrees of crosslinking by divinylbenzene were studied by thermogravimetry, differential scanning calorimetry, infrared spectroscopy and Raman spectroscopy. The results showed that thermal decomposition temperature of the beads was raised with increased crosslinking in the porous beads, suggesting that their thermal stability could be greatly improved by crosslinking as expected. DSC analysis revealed that porous beads with crosslinking degrees less than 30% tin weight) had a glass transition and that its temperature (T-g) was gradually changed from about 100 degreesC (T-g of linear polystyrene) to 160 degreesC as the crosslinking was increased. However, T-g disappeared and an exothermic peak around 165 degreesC was found for highly crosslinked beads with more than 30% of crosslinking. The exothermic peak might be attributed to the coupling reaction and/or thermal polymerization of pendant double bonds at high temperature as proved by IR and Raman spectra. When crosslinking was less than 10%, a melting process could be observed as an endotherm at about 270 degreesC. Otherwise, if the crosslinking was above 15%, no melting was displayed and instead of it an exothermic phenomenon took place between 250-350 degreesC. The exotherm might be due to the decomposition of some groups formed in the preparation and storage of the beads. (C) 2001 Elsevier Science Ltd. All rights reserved.