OXIDATIVE CROSS-LINKING OF ALKYD RESINS STUDIED WITH MASS-SPECTROMETRY AND NMR USING MODEL COMPOUNDS

The crosslinking of alkyd resins has been studied using ethyl linoleat e and methyl ricinoate as model compounds. With quantitative C-13 NMR is was established that ether- and peroxy-crosslinks were formed in ro ughly equal amounts. Double bonds reacted to give epoxides, endoperoxi des, and beta-scission into aldehydes. Using SIMS it was established t hat dimers through pentamers were formed having included several oxyge n atoms. After reduction of peroxide (crosslinks) with stannous chlori de, the higher oxygen homologues decreased. In the NMR spectrum of the reduced material, peroxide and epoxide signals completely disappeared . High resolution electrospray ionization mass spectra (ESI-MS) yielde d evidence regarding the crosslink mechanism. The non-conjugated linol eic acid was found to crosslink by combination of radicals: dimers wer e having masses 2(M-1). The conjugated linoleic acid crosslinked by ad dition of radicals to the double bond and disproportionation, yielding masses 2M as well. (M = mass of ethyl linoleate or methyl ricinoate, respectively, including several oxygen atoms.) EIS-MS of oligomers aft er isotopic exchange enable estimation of OH and OOH groups.