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

A typical room-temperature vulcanised, foamed, silica-filled siloxane rubbe r has been characterised using FTIR(ATR), SEM, density measurements and mea surements of swelling in toluene vapour. The results show that the foamed P DMS rubber is an open-cell structure with a void fraction of 50% of the tot al volume. Long term stability was assessed by degrading the material at hi gh temperatures (180-200 degreesC) in air. Changes in FTIR (ATR) were not n oticeable, except rapid loss of peaks due to the catalyst and its solvent. The material showed a small, but statistically significant, increase in den sity and decrease in equilibrium swelling. The most sensitive method to mea sure degradation was chemiluminescence (CL), which confirms that the PDMS i s extremely stable because the CL intensity is weak as compared to carbon c hain polymers. Removal of oligomers and catalyst residues by toluene extrac tion results in the disappearance of initial decay and removal of peroxide residues by treatment with nitric oxide also confers greater oxidative stab ility. Ramped chemiluminescence in air shows that the PDMS residue after to luene extraction is more stable than the virgin material, indicating that d egradation is due to small fragments and catalyst solvents rather than the main siloxane network. (C) 2001 Elsevier Science Ltd. All rights reserved.