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Published on March 8, 2019

Improving low temperature properties in a silicone elastomer

This article describes the investigation and commercialization of a specific compound intended for a cryogenic seal application. A hypothesis to account for the improvement in low-temperature performance is discussed and extended to other potential chemistries and applications.
It is well known in the elastomers industry that dimethyl silicone elastomers exhibit a dramatic increase in their modulus at temperatures at about -40°C. Historically, phenyl substituted dimethyl siloxane polymers (PVMQ) have been used to achieve consistent mechanical properties in silicone elastomers at these low temperatures.
We have found that improved low temperature properties can be achieved through incorporation of a medium viscosity, vinyl terminated diphenyl dimethyl copolymer into a conventional vinyl dimethyl gum (VMQ). This modified VMQ gum was combined with filler and processed into a low temperature base.
The low temperature base was combined with additional VMQ high consistency rubber base and catalyst for molding into test articles and finished seals.
The effect on the mechanical properties were assessed for a range of viscosities of the vinyl diphenyl dimethyl copolymer, for the degree of phenyl substitution on the copolymer, for the base processing and catalyst choices for the compound.

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