Crosslink mechanisms of high-solids alkyd resins in the presence of reactive diluents

The drying of alkyds was studied using NMR and mass spectrometry employing model compounds. Crosslinking occurs via oxidation of unsaturated fatty (li noleic) acids in the resin. Hydroperoxides formed as intermediates are degr aded to alkoxy and peroxy radicals by cobalt catalyst. These radicals then recombine to form mainly ether and peroxy crosslinks. However, with conjuga ted fatty acids another mechanism prevails in which addition of radicals to the double bonds occurs. Despite the differences in mechanism the rates of both reactions were found to be similar. High-solids alkyd coatings may em ploy reactive diluents replacing traditional solvents (white spirit). The r ate of incorporation of these reactive diluents into the actual paint film during drying can be followed with NMR. Allyl ether groups appear to react fastest whereas allyl esters show generally Little reactivity, Using mass s pectrometry it was found that incorporation involves recombination of radic als as well. However, reactive diluents with conjugated double bonds will b e incorporated by radical addition. (C) 2000 Elsevier Science S.A. All righ ts reserved.