Modified polydimethylsiloxane rubbers

Recent work has focused on a variety of thermoplastic elastomers and modified thermoplastic polyimides based on the aminopropyl end functionality present in suitably equilibrated polydimethylsiloxanes. Characteristic of these are the urea linked materials described in references 22-25. The chemistry is summarized in Scheme 7. A characteristic stress-strain curve and dynamic mechanical behavior for the urea linked systems in provided in Figures 3 and 4. It was of interest to note that the ultimate properties of the soluble, processible, urea linked copolymers were equivalent to some of the best silica reinforced, chemically crosslinked, silicone rubber... 

Epoxies modified with butadiene acrylonitrile copolymers with (32) amine or carboxy end groups have disadvantages. They are susceptible to thermal and oxidative degradation and also have poor hot/wet properties, i.e., they soften when exposed to heat and moisture for long periods. Polysiloxane rubbers such as polydimethylsiloxane have been considered as a possible alternative. 

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