Polymerisationen und polymerisationsinitiatoren, 16. Einfluß von Thioxo-Gruppen in barbitursäurederivaten auf die polymerisationsauslösung von methacrylsäure-methylester

In the presence of Cu²⁺ and Cl^? ions as well as atmospheric oxygen 5-alkyl-1,3-dimethylbarbituric acids initiate the radical polymerisation of methyl methacrylate. If a thioxo group is introduced in position 2 of the barbituric acid, initiating capability is slightly increased; thioxo functions in position 4 or 4,6, on the other hand, suppress initiation almost completely. In this case, the radicals formed at C-5 are stabilized by the neighbouring thioxo groups and dimerize at the sulfur atoms, yielding disulfides. Thus, these thiobarbituric acids may act as inhibitors. In the case of Cu(II)-catalyzed initiation, this inhibiting effect is enhanced by formation of almost insoluble Cu(I) thioxobarbiturates.