Photoexcited state acceptor monomers as initiators for free radical induced polymerization

Photoinduced alternating copolymerization can be accomplished without the presence of a conventional free radical generating photo-initiator. The structural influences in the direct photolysis of N-Alkyl and N-Arylmaleimides as well as their corresponding ground state charge transfer complexes (CTC) with suitable donors have carefully been investigated. In this paper, laser flash photolysis has been used in order to clarify and experimentally provide evidence for the mechanism of initiation. The maleimide transient intermediate generated by flash photolysis is readily quenched by typical triplet quenchers such as cyclohexadiene. Furthermore, self quenching and reduction of MI transient lifetimes as a function of increasing concentrations of typical hydrogen donors have been determined. Stern-Volmer quenching rate constants for direct versus electron transfer hydrogen abstractions are calculated and compared to benzophenone (BP). From these comparisons it is clear that the triplet state MI is more efficient in direct H-abstraction than the corresponding triplet state of BP. Finally, much higher values of the quenching rate constant for the MI/tert. amine pair versus the MI/ alcohol pair were calculated, suggesting an electron transfer process