A new class of photopolymers with pendent dimethylmaleimide groups. II. Photocrosslinking of homo- and copolymers of N-(5-methyl-3-oxa-4-oxohexen-5-yl)-dimethylmaleimide

The polymerization of N-(5-methyl-3-oxa-4-oxo-hexen-5-yl)-dimethylmaleimide (DMI-MA) yields poly(methacrylates) with pendent light sensitive dimethylmaleimide (DMI) groups. A series of DMI-MA homopolymers with different molecular weights (60.000–520.000) and a series of copolymers of DMI-MA with methylmethacrylate (MMA) with varying DMI content (6–78 mol-%) were prepared. DMI-containing polymers show high photosensitivity (6 mJ cm^?2 at 365 nm). Exposure energies to insolubilize thin solid photopolymer coatings sensitized with thioxanthone were determined with monochromatic radiation at 365 nm by two different methods: by the photographic step tablet method for coatings on copper substrates and by establishing the gel point exposure for coatings on transparent quartz supports. Minimum exposure energies are linear functions of the molecular weight and of the DMI molar fraction of the polymers. Sensitivity as a function of the sensitizer concentration shows a maximum. The results agree well with theories of photocrosslinking.