Co-operative degradation in thin films of poly(methyl methacrylate) and poly(ethylene terephthalate)
The interaction between thin films of polymethyi methacrylate and polyethylene terephthalate is reported. Studies of bulk PET/PMMA blends reveal that a direct ester exchange reaction occurs between the two polymers, and this information is used in the investigation of thin film interfaces between PET and PMMA. Discrete wavelength ellipsometry has been used to study the thermal decomposition of thin films of PMMA , and the crystallisation of thin films of PET. It is found that, below ~ 74.5 nm (6 x R(_g), the rate of degradation of PMMA (M(_N) ~ 44,000), increases with decreasing film thickness. For films < 100 nm , the rate of crystallisation of PET (M(_N) ~ 23,000), is found to decrease with decreasing film thickness. Using data obtained from neutron reflectometry, the equilibrium interfacial width between PET and dPMMA is measured. At an annealing temperature of 493K, the interface is broadened by crystalline roughness in the PET phase, and the maximum interfacial width is found to be ~7.7tmi. At 573K, despite extensive degradation of dPMMA, an equilibrium interfacial width of ~5nm is achieved. Capillary wave broadening and the effects of asymmetry are considered. A detailed analysis of Interfacial Marker Movements, reveals that there is an asymmetric broadening of the gold markers towards the PMMA side of the interface, indicative of a grafting reaction between PET and PMMA or a crosslinking reaction within the residual PMMA layer. The degradation of PET films, treated with acrylic based coating formulations has been studied by GPC, UV-vis spectrophotometry, and weight loss techniques. The rate of chain scission at 563K is seen to be dependant on the the concentration of tri methoxy methyl melamine (TMMM), the coating crosslinking agent.