Effect of Molecular Weight on the Cross-linking of Siloxanes by High-energy Radiation

Abstract

RECENT work has shown that many long-chain polymers^1,2 can be cross-linked by high-energy radiation; although polymers containing only carbon atoms in the main chain have been studied in great detail, the same effect has been observed in polymers in which the main chain comprises alternating carbon and oxygen atoms (‘Carbowax’) or silicon and oxygen (silicones). There is a considerable amount of evidence to show that for a given polymer the density of cross-linking (that is, the proportion of monomer units which are linked) is directly proportional to the radiation dose over a wide range. This renders it possible to prepare a series of samples of known (relative) densities of cross-linking. Absolute values of the density of cross-linking may be evaluated in a number of ways, including swelling measurements and determination of the minimum radiation needed to form an insoluble network or gel in a polymer of known average molecular weight.