Aspects of amino functionalization of polypropylene surfaces for adhesion promotion of thermally-evaporated copper films

摘要

The relevance of amino gioups for adhesion is discussed in the framework of copper metallization of amino-functionalized polypropylene (PP) surfaces Results from radio-frequency plasma polymerization processes in pulsed and continuous wave modes are presented for 1,2-di-aminocyclohexane (DACH) and allylamine homo-polymerization, and allylamine-butadiene co-polymerization. The latter allowed precise control of the nitrogen and amino groups concentrations in the resulting plasma co-polymers, which was shown to affect the surface free energy. Surface densities of more than 30 nitrogen groups and up to 9 primary amino groups per 100 carbon atoms were found. Primary amino groups were quantified by XPS analysis after gas phase derivatization with pentafluorobenzaldehyde. The stability of the plasma polymers was studied for storage in air. During storage, a significant oxygen uptake by the films and a decay of primary amino groups were observed The peel strength of copper on allylamine plasma polymers showed a positive correlation to the amino group density, the locus of failure being in the weak boundary layer (WBL) of PP. For DACH plasma polymers, a cohesive failure occurred within the DACH polymer As a general feature of amino functionalization by plasmas, a significant rise in oxygen content during contact with air does not allow to distinguish adhesion-promoting contribution of copper-amino group interaction independently from that of copper-oxygen group interaction.