RADIATION-CHEMISTRY ASPECTS OF POLYMERIZATION AND CROSS-LINKING - A REVIEW AND FUTURE ENVIRONMENTAL TRENDS IN NONACRYLATE CHEMISTRY

Radiation induced polymerization of acrylate based materials has been in industrial use for almost twenty years. This field is still growing rapidly and the advantages of the technology, e.g. being solvent free and rapid 'cure', are very attractive properties from an industrial a nd environmental point of view. Mixtures of mono- and multifunctional acrylates are today the 'heart' of radiation curable systems. However, serious concerns about the health hazards connected with the handling of the liquid coating is an important issue. Different approaches to overcome this problem have been addressed and the obvious thing to sta rt with was the investigation of a great number of acrylates regarding their potential health effects. Acrylates do exhibit some specific un attractive properties, regarding their toxicology profile. Sensitizati on and skin irritation are considered to be limiting factors for a con tinuing rapid expansion of this successful technology. A further devel opment and improvement of the photoinitiator chemistry together with a more efficient use of high powered irradiators with a narrow bandwidt h distribution, will improve still the acrylate technology. The import ance of degree of conversion of carbon-carbon double bonds as a functi on of dose rates, i.e. residual unpolymerized acrylic monomers, will b e discussed. An additional approach, since the acrylate technology is well established, is to further optimize the 'reactivity' and conversi on on 'new' acrylates in order to obtain maximum conversion, thus mini mizing the residual amount of monomers that can migrate out of the coa ting. The increasing functionality of the acrylate/oligomer will of co urse result in an increasing probability of monomer/oligomer being att ached to the crosslinked network. Furthermore, this paper emphasizes p otential acrylate replacements, and 'new' or alternative chemistry for acrylates will be introduced. The state of the art and the associated problems for cationically induced polymerization, free radical altern ating copolymerization, hybrid systems and direct photolysis of donor/ acceptor pairs are discussed.