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In several recent reports, the efficient photoinitiated polymerization by excitedstate maleimides have been shown in numerous acceptor / donor pair combinations 1-10] The strong hydrogen abstractability of the excited triplet state Ml has also been evaluated in initiation of acrylate polymerization and the importance of available abstractable hydrogens has been verified 11]. The unique feature of maleimides in general is its dual effect of simultaneously acting as a photoinitiator and as a polymenzable monomer. Once the initiation by photolysis of Ml / H-donors has generated a sufficient number of radicals, the ground state Ml will copolymerize with the selected monomers chosen.
Although the influence of structural variations of the maleimide N-substituent , average functionality, temperature, light intensity, donor structure and Ml / donor ratio have been carefully investigated, very little information regarding the initiating mechanism has been reported. Laser flash photolysis has been used in order to clarify and experimentally provide evidence for the mechanism of initiation 12]. The maleimide transient intermediate generated by flash photolysis is readily quenched by typical triplet quenchers such as cyclohexadiene. Furthermore, selfquenching and reduction of Ml 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 Ml is more efficient in direct Habstraction than the corresponding triplet state of BP. Finally, much higher values of the
quenching rate constants for the MI / tert. amine pair versus the MI / alcohol pair were calculated, suggesting an electron transfer process.
