A high performance size exclusion chromatographic study on the depth-dependent gradient in the molecular weight of aged triterpenoid varnish films

The depth-profiles of aged triterpenoid resin films, dammar and mastic, were uncovered by optimized krypton fluoride excimer laser ablation (248 nm, 25 ns) and the etched varnishes were examined by high performance size exclusion chromatography (HP-SEC). The use of two detectors monitored the molecular weight distribution across depth as a function of absorbance at ultraviolet (240 nm) and visible (400 nm) light. The absorption of the films at both wavelengths is separated in a small fraction of sesquiterpenoids (200 Da), triterpenoid molecules (400/500 Da), dimerized and oxidized triterpenoid molecules (900-1000 Da) and condensed entities (10-80 kDa) that are formed upon the radical polymerization of polycadinene and cis-1,4-poly-beta-myrcene, which are the polymers of dammar and mastic, respectively. The results establish the generation of depth-dependent gradients in radical polymerization, condensation and cross-linking across the depth-profiles of the triterpenoid films as a consequence of aging.