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Technological advances have made photopolymers increasingly important for applications in fields as different as a printing, coating, microlithography, and electronic device manufacturing. Compared with other photosensitive materials such as silver halides and electrophotography, the of photopolymers is not high and requires ultraviolet light with energy densities of 10-100 mJ/cm for exposure. If the sensitivity can be enhanced, photopolymers will have potential for applications in terms of direct laser imaging such as "computer-to-plate" system and holographic recording. Of the various mechanisms in photopolymer systems, photopolymerization has the highest potential for high sensitivity since it contains chain reactions of monomeric compounds. In the photopolymerization mechanism, photosensitive layer consists of three essential components, photoinitiator, monomer, and matrix polymer. While all the three components influence the sensitivity, the spectral sensitivity of photosensitive layer is governed only by that of photoinitiator. In addition to the photoinitiator, matrix polymers also play a significant role in sensitivity enhancement. For example, a poly(N-vinyl-2-pyrrolidone) (PVP) matrix remarkably enhances the sensitivity of the photopolymer layers due to the acceleration of the polymerization rate of the monomers. The sensitivity of a thin photopolymerizing layer increases from 10 2 to 0.3 2 when the matrix polymer is changed from poly(acrylate-co-acrylic acid) to PVP. However, the strong hydrophilicity of PVP limits the practical application of this photosensitive layer except for holographic recording. Recently several reports have been published on photopolymers using microgels. Kanda reported that ultraviolet sensitive polymers consisting of microgels provided an improved coating and adhesion 1] Michael and co-workers studied the characteristics of an ultraviolet light sensitive coating consisting of a monomer, photoinitiator, and microgels as a heterogeneous matrix 2] To clarify the effect of microgels as matrix polymer they prepared another material with an almost identical composition except for the matrix polymer, in which polyacrylate was used as a homogeneous matrix. Comparison of the two photopolymers showed that the former exhibited the higher photosensitivity. However, it was also noted that the film-forming property of those microgels was not sufficient by themselves, and that the addition of some homogeneous polymeric compounds was required to form appropriate photosensitive coating layer. Funke et aL, prepared microgels by polymerizing bifunctional acrylate monomers such as divinylbenzene and ethylene glycol dimethacrylate using an 3] These microgels were inadequate in dispersion and required considerable amount of emulsifier to remain stable in dispersion. Fukuchi recently reported preparation of a photopolymer using microgels containing vinyl groups, stating that it was water-developable and facilitated a physically good film layer, but the author did not discuss the details of 4] Recently a new concept for sensitivity enhancement has been developed which involves the use of surface activated microgels as a heterogeneous polymer matrix. This paper describes the preparation of the surface modified microregels, and effects of those microgels on photopolymerization rate and the sesitivity enhancement.
