STRUCTURAL STUDY OF A VARNISH BY ELECTRON-SPIN-RESONANCE

Related to the study of interactions between food and aluminum cans, s tructural features of a vinylic organosol coating were studied by elec tron spin resonance (ESR). Paramagnetic probes were incorporated separ ately in the normal formulation of a widely used varnish, which was th en cured at high temperature for different times. The behavior of amin oxyl probes, differing by their volatility and their functional groups , was studied. When 4-amino-2,2,6,6-tetramethylpiperidinoxy (3) was us ed as probe, it grafted onto the polymeric chains during curing. Two t ransitions could then be observed, corresponding to NO. in two environ ments, which were assigned to the PVC (T-fs, 132-142 degrees C) and to the epoxyphenolic (EP) (T-50G, 142-152 degrees C) phases of the varni sh. This was confirmed by a separate study of the PVC and EP constitue nts. Both transition temperatures depended on the extent of curing, su ggesting that the PVC phase was plasticized by reactive constituents o f the coating. The transition temperatures were also influenced by the extent of penetration of the PVC in the EP phase. Probes which could not graft on the polymer were lost by volatilization during curing. (C ) 1996 John Wiley & Sons, Inc.