Self Accelerating Decomposition Temperature - Application To Polymerizable Mixtures

Application To Polymerizable Mixtures

Some mixtures containing peroxides and polymerizable monomers may also exhibit SADTs. For example, mixtures of vinyltrimethoxysilane, peroxides and stabilizers are used commercially for cross-linking polyethylene to make PEX pipe. These mixtures are typically liquid solutions that are shipped to where they are used to graft alkoxysilane groups to polyethylene. In such mixtures decomposition of the peroxide can initiate exothermic radical polymerization of the vinyltrimethoxysilane. At low temperature the decomposition rate is slow enough that the stabilizers quench the polymerization before much heat is generated and the container dissipates what heat is produced. At higher temperatures peroxide decomposition is faster, more polymerization occurs to heat the mixture, which in turn increases peroxide decomposition and polymerizes the monomer even faster. The container dissipates heat more slowly in a higher-temperature envirnment, so at some critical temperature heat is generated by polymerization faster than the container can dissipate it and the reaction self-accelerates. Thus such a mixture has a SADT that depends on container size exactly as in the case of a pure organic peroxide.