Catalytic chain transfer
Catalytic chain transfer (CCT) is a process that can be incorporated into radical polymerization to obtain greater control over the resulting products. Introduction Radical polymerization of vinyl monomers, like methyl (metha)acrylate of vinyl acetate is a common (industrial) method to prepare polymeric materials. One of the problems associated with this method is, however, that the radical polymerisation reaction rate is so high that even at short reaction times the polymeric chains are exceedingly long. This has several practical disadvantages, especially for polymer processing (e.g. melt-processing). A solution to this problem is catalytic chain transfer, which is a way to make shorter polymer chains in radical polymerisation processes. The method involves adding a catalytic chain transfer agent to the reaction mixture of the monomer and the radical initiator. Historical background Boris Smirnov and Alexander Marchenko (USSR) discovered in 1975 that cobalt porphyrins are able to reduce the molecular weight of PMMA formed during radical polymerization of methacrylates. Later investigations showed that the cobalt dimethylglyoxime complexes were as effective as the porphyrin catalysts and also less oxygen sensitive. Due to their lower oxygen sensitivity these catalysts have been investigated much more thoroughly than the porphyrin catalysts and are the catalysts actually used