The heat ageing interaction of silicone rubber with three of fumed silica having different surface property was studied. The rubber compounds and vulcanizates were swelled in toluene and in toluene over ammonia; bound rubber as well as swelling degree of the vulcanizate were determined. It was found that a significant amount of chemical crosslink is formed between filler and rubber chain upon heat treatment

meanwhile the interfacial hydrogen bond is transformed to chemical linkage. The formation of chemical linkage as well as hydrogen bondis greatly reduced by surface modification of the filler before or during compounding.