Syntheses of High Sensitive Photocrosslinking Reagents and Their Application to Visible Light (Laser) Sensitive Polymer Systems.

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We have found that benzoquinones are very effective photocrosslinking reagents for polymers and that some of them are very sensitive to visible light. In this study we have investigated the photocrosslinking mechanism of polymers with benzoquinones and, at the same time, on the basis of the mechanism we have investigated preparation methods of visible light (especially, laser) sensitive polymers by the use of benzoquinones. The photocrosslinking of poly(methyl methacrylate) (PMMA) by p-benzoquinone proceeded via a free radical mechanism and the introduction of alkyl groups as substituents to p-benzoquinone depressed the activity in the photocrosslinking. On the other hand, in the photocrosslinking of polymers which have pendent epoxy or epithio groups, alkyl(e.g., ethyl or t-butyl) group subsitituted benzoquinones were more effective than p-benzoquinone. This photocrosslinking was explained by ring opening polymerization of pendent groups. Moreover, alkylthiobenzoquinones have an absorption maximum between 400 and 500nm,and were very effective in the visible light ( <lambda> >370nm) induced crosslinking of the polymers which had episulfide groups. Quinonoid units bound to polymer chains were found to play an important role in the photocrosslinking of PMMA by p-benzoquinone. On the basis of this finding, preparations of the polymers bearing pendent quinonoid groups were examined. The copolymer of methyl methacrylate bearing benzoquinonylthioacetoxy groups were prepared and found to be very sensitive to visible light in spite of its low content. Polyurethanes bearing quinonylthio groups were also prepared. Although the content of functional groups could be increased, the rates of their photocrosslinking were pretty low. The addition of another alkanediol to the polyurethanes and the use of aliphatic diisocyanate instead of aromatic one improved their photocrosslinking rates.