ABSTRACT
However, a detailed knowledge of the chemical reactions at the surface, the spatial rearrangement of segments or of the whole macromolecule and exact information on changes in molecular weight distribution (MWD) of polymers occurring during plasma exposure is lacking. The oxidation pathways of polymer surfaces in an oxygen plasma were commonly explained by means of photo oxidative-like reactions on the basis of XPS, SIMS or IR-ATR (Attenuated Total Reflection) data8-14. In 1966 the process of Crosslinking by Activated Species of INert Gases (CASING) was introduced by Hansen and Schonhorn15. Hudis found that the gel formation during exposure of polymers to hydrogen plasma was due to the action of intense plasma vacuum UV radiation (VUV)16. Some efforts were made to use the plasma-induced crosslinking as a polymer surface modification technique with applications in adhesion improvement and barrier formation. These investigations brought more insight into degradation reactions of PET8. In a series of papers we have shown by XPS, NEXAFS (Near Edge X-ray Absorption Fine Structure spectroscopy), SEIRA (Surface Enhanced Infrared Absorption spectroscopy) and adhesion tests that optimal surface modification can be obtained with 0.1 to 2 s short plasma pulses17-24. Longer treatment leads to a strong degradation of the polymer structure and orientation and often to a decrease in bondability21,25. It is assumed that at longer exposure times low-molecular weight degradation products cover the surface and form a Weak Boundary Layer (WBL) which is detrimental for good adhesion. Therefore, the
effects of different plasma treatments on the molecular weight of polymers were also examined in this study.
