Photochemistry of N-Substituted Maleimides

摘要

Photoinitiated free radical polymerization of donor / acceptor type monomers have gained considerable interest due to the possibility of formulating UV curable non-acrylate systems. Recently, we described a photoinitiator free system based on donor / acceptor combinations. Photoinitiator free nonacrylate based compositions will of course attain an enhanced interest and importance because of a broader selection of raw materials and combinations thereof, potential outdoor use, lower costs of formulations, improved odour, no formation of benzaldehyde, less extractables and so on. Recent developments of the direct photolysis of these acceptors and complexes, and their potential use in practical "UV curing" will be outlined. by a selective combination of A and D type monomers, a direct photolysis of the ground state complex (CTC) or the excitation of the acceptor, followed by the formation of an exciplex, will initiate a free radical copolymerization. A second route of direct initiation is based on inter or intra molecular H-abstraction from an excited state acceptor or exciplex. This paper will emphasize on the photochemistry of maleimides as it relates to initiation of polymerization depending on acceptor and donor strength of the monomer system. Inherently different reactivities between vinyl ethers and p-alkoxystyrenes as donors and N-alkylmaleimides as acceptors are compared to photoinitiator containing acrylates. Furthermore, the ratio of homo and alternating copolymerization as well as the 2+2 cycloaddition will be discussed.