Characterisation and oxidative degradation of a room-temperature vulcanised poly(dimethylsiloxane) rubber

A typical room-temperature vulcanised, foamed, silica-filled siloxane rubber has been characterised using FTIR(ATR), SEM, density measurements and measurements of swelling in toluene vapour. The results show that the foamed PDMS rubber is an open-cell structure with a void fraction of 50% of the total volume. Long term stability was assessed by degrading the material at high temperatures (180–200 °C) in air. Changes in FTIR (ATR) were not noticeable, except rapid loss of peaks due to the catalyst and its solvent. The material showed a small, but statistically significant, increase in density and decrease in equilibrium swelling. The most sensitive method to measure degradation was chemiluminescence (CL), which confirms that the PDMS is extremely stable because the CL intensity is weak as compared to carbon chain polymers. Removal of oligomers and catalyst residues by toluene extraction results in the disappearance of initial decay and removal of peroxide residues by treatment with nitric oxide also confers greater oxidative stability. Ramped chemiluminescence in air shows that the PDMS residue after toluene extraction is more stable than the virgin material, indicating that degradation is due to small fragments and catalyst solvents rather than the main siloxane network.