ILLUSTRATION OF SURFACE CROSS-LINKING OF DIFFERENT POLYMERS TREATED IN ARGON PLASMA

The influence of argon plasma on polycarbonate (PC) and poly(propylene ) (PP) has been studied in terms of structural changes and reaction me chanisms. In situ UV-visible ellipsometry reveals formation of a surfa ce layer with a higher refractive index than the untreated polymer. Th e increase in the refractive index is attributed to polymer densificat ion, which is assigned to crosslinking. However, a decrease in the ave rage molecular weight of the PC is also observed and two populations o f macromolecules of different size are detected by light scattering me asurements, revealing a competition between crosslinking and degradati on. The reaction mechanisms were investigated using Nuclear Magnetic R esonance (H-1 NMR) and in situ IR ellipsometry. Degradation is caused by carbonate bond breaking, while crosslinking seems to be related to a decrease in methyl groups. The ellipsometry results are correlated w ith amorphous phase extraction and H-1 NMR analysis of modified PP. Th e crosslinking mechanism involves the elimination of methyl groups, an d also the formation of exomethylenic bonds. Spectroscopic ellipsometr y appears to be a valuable tool to study the interaction between a pla sma and a polymer, as UV-visible ellipsometry is sensitive to structur al changes in the polymer, while IR ellipsometry detects the appearanc e and disappearance of chemical groups in a surface layer.