Acrylic monomers, photoinduced

As reported in Table 15, the kinetic data clearly indicate that the photoinitiation activity of poly(BMOA-co-MtA) is not substantially affected by the content of BMOA co-units along the polymer chain and is of the same order of magnitude as that found for the model compound BMOAc. The absence of a polymer effect in the above photoinitiators has been interpreted [84] in terms of a photodegradation mechanism of the macromolecules involving the ftee radical species anchored to the main chain, even in the presence of acrylic monomers, analogous to what is reported in Scheme 18. Moreover, the induction period of the HDDA/BA photoinduced polymerization increases, on decreasing the content of... 

There has been much interest in the role and efficiency of amine co-synergists in photoinduced addition polymerisation of acrylic monomers. Several approaches have been undertaken in this regard one of which involves the use of amine synergists... 

Mixtures of photoinitiators have been actively studied. Michler s Ketone and benzoyl peroxide have been shown to effectively induce the photopolymerisation of methyl methacrylate through the formation of an initial complex shown in scheme 3 7, Although the exact initiating radical does not appear to be ascertained it is almost certainly the arylalkylamino radical from the Michler s Ketone. In the interaction of benzil and thioxanthone with triethylamine in the photoinduced polymerisation of acrylic monomers their is a competition between reverse electron transfer and ketyl radical formation . As the carbonyl concentration increases the bimolecular termination rates due to radical recombination increases. The same workers also studied the same system but replaced the ketone initiators with pyrene . Their inability to identify pyrene end groups indicated that the active initiating species arise from a complex between the pyrene and the triethylamine. 

The results in Table III show the effect of various amines of different ionisation potential on the photopolymerisation of 2-hydroxyethylmethacrylate in nitrogen saturated water initiated by the benzophenone with the structure 2. As found earlier for the water soluble thioxanthones ( ), the percentage photoconversion decreases with increasing ionisation potential of the amine. In all of these experiments, oxygen had a strong quenching effect on the photopolymerisation. It would appear, therefore, that in aqueous media the photoinduced polymerisation of the acrylate monomer occurs solely via the lowest excited triplet state of the benzophenone molecule to form an exciplex with the amine co-synergist (Schemel ). 

Several examples of the structures of typical multifunctional acrylic monomers (35-40) used in photoinduced radical cross-linking polymerizations are depicted below ... 

CuAAC provides a facile entry to a wide variety of triazole-based polymers with very high synthetic efficiencies as compared to other cross-linking methods such as photoinduced cross-linking of acrylate-functionalized monomers, photoinduced thiol-ene conjugation, or Michael addition type conjugation between thiol and acrylate or vinyl sulfone precursors. Due to the presence of the acidic triazole C-H and lone pair electrons on the nitrogen atoms, such triazole-based polymer... 

The cationic photoinduce process present some advantages compared to the radical one [10] in particular lack of inhibition by oxygen, low shrinkage and good adhesion and mechanical properties of the UV-cured materials. Moreover, the monomers employed are generally characterized by being less toxic and irritant with respect to acrylates and methacrylates, largely employed in radical photopolymerization. 

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