Structural characterization of modified rosins by matrix-assisted laser desorption/ionization mass spectrometry

Abstract

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was applied to the structural characterization of rosin-glycerin ester and rosin-resol resin reactant as the model compounds of rosin-modified phenol resin. As for the rosin-glycerin ester sample, sodium cationized di- and triglycerides of the rosin acids were mainly observed as major products, whereas those of monoglycerides were scarcely observed on the MALDI mass spectrum. Considering the isotope distribution, the composition of the rosin acid in the glyceride was estimated as abietic acid/dehydroabietic acid = ca. 70/30, whereas that in the original rosin acid was ca. 95/5. This fact demonstrated that a considerable amount of abietic acid was transformed to the dehydroabietic acid structure. On the other hand, as for the rosin-phenol resin reactant sample, resol resin oligomers having rosin acids at both terminals were observed as the main components in the range of the degree of polymelyzation n = 1 to 8, while those having a rosin acid at one terminal side were also observed as minor components mainly at a lower mass range under m/z 1000. Moreover, the detailed distribution among the observed ions suggested that the dehydration in the abietic acid also fairly took place during the reaction between the rosin acids and the resin.