Physical properties of addition silicones as a function of composition.

The effects of molecular weight of the base silicone, filler and copolymer concentrations on compression set, strain, creep and dynamic elastic modulus were determined. The molecular weight of the base silicone had the least effect on these properties although low molecular weights showed better properties. Chain extenders were detrimental to physical properties of creep, compression set and dynamic elastic modulus. Increased copolymer concentrations decreased compression set, strain and creep and increased the dynamic elastic modulus. The useful copolymer/base functional group ratio was from 1:1 to 3:1. Filler affected properties to a lesser extent than copolymer ratio. Compression set, strain, and creep decreased and the dynamic elastic modulus increased with increasing filler with the properties being directly proportional to the weight fraction. All properties were interrelated with ln strain linearly related to ln compression set, creep proportional to set, and the dynamic elastic modulus was inversely correlated with strain and creep.