SOME ASPECTS OF THE ROLE OF AMINES IN THE PHOTOINITIATED POLYMERIZATION OF ACRYLATES IN THE PRESENCE AND ABSENCE OF OXYGEN

Triethanolamine (1), N-methyldiethanolamine (2) and N,N-dimethylethano lamine (3) have been used in conjunction with the 2-(2-chlorophenyl)-4 ,5-diphenylimidazolyl radical and triplet benzophenone to initiate the polymerisation of lauryl acrylate. The radical abstracts a hydrogen a tom from the amine to generate an alpha-aminoalkyl radical. From the o rder of reactivity of the amines towards the lophyl (triarylimidazolyl ) radical i.p. 2 >> 1 > 3 it is concluded that hydrogen-atom abstracti on occurs rather than electron followed by proton transfer. The imidaz olyl radicals abstract hydrogen from thiols in a similar fashion more effectively to give thiyl radicals which initiate polymerisation of th e acrylate. By following the progress of the polymerisation reactions by RTIR spectroscopy, it was concluded that the effectiveness of the a mines to reduce oxygen inhibition is 1 < 3 < 2. The ability of the ami nes to act as synergists in the polymerisation of thin films of lauryl acrylate initiated by lophyl radicals and tripler benzophenone was as sessed. The efficiency of the amines was found to be 2 similar to 1 > 3 for reaction with lophyl radicals whereas with triplet benzophenone the three amines gave similar amounts of polymer. For amines 2 and 3. two types of amino alkyl radical can be generated. It is concluded tha t radicals of type > NCHCH2OH are more effective initiators than CH2N <.