MECHANISTIC STUDY OF DRYING OF ALKYD RESINS USING ETHYL LINOLEATE AS A MODEL SUBSTANCE

Air drying of alkyd resins under the influence of cobalt driers was st udied using ethyl esters of fatty acids as model compounds. In order t o get insight into the crosslink reactions taking place during initial drying as well as through-hardening of alkyds the reaction was follow ed for a considerable period of time using several analytical techniqu es. Ethyl linoleate appeared to react completely in three days whereas the oleate required more than three months for a similar conversion. Crosslinks were detected using POMMIE C-13 NMR, a technique which yiel ds a carbon NMR spectrum having separate traces for methine, methylene and methyl carbons. Broad methine carbon signals around 73 and 83 ppm indicated the presence of ether and peroxy crosslinks, respectively. Remaining double bonds gave a signal at 120-140 ppm. The relative inte nsity of these signals changed over a period of one year, indicating f urther reaction of double bonds to form ether crosslinks. These reacti ons are therefore likely to occur during through-hardening of alkyds. Crosslinking yielded oligomers up to the pentamer as was demonstrated with size exclusion chromatography (SEC). With secondary ion mass spec troscopy (SIMS) five groups of lines were obtained, the individual lin es within each group being 16 mass units apart. The results point to t he formation of oligomers with various amounts of oxygen, including no n-oxygenated oligomers. Fast atom bombardment MS (FAB-MS) and direct c hemical ionization-MS (DCI-MS) gave a similar distribution for the dim er and the trimer, respectively. Quantitative determination by means o f GC indicated the C-C linked oligomers to be formed in minor amounts.