ON THE SECONDARY RELAXATION OF SUBSTITUTED BIS-A POLYCARBONATES

The relaxation behavior of substituted bisphenol-h polycarbonates is i nvestigated in the glassy state by mechanical spectroscopy. Convention al bisphenol-A polycarbonate (BA-PC) is compared with polycarbonates b ased on 1'-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (TMC-PC) an d 1,1'spiro[bis(3,3-dimethyl-6-hydroxyindane)] (SRI-PC) and random cop olymers of the latter with bisphenol-A. In SBI-PC the phenyl flip is n ot just hindered but completely locked due to the chemical bridge via the spiro linkage. Despite the impossibility of phenyl motion, the gam ma-relaxation is observed for SBI-PC at roughly the same temperature a s for the other two polycarbonates. This is real proof that the phenyl motion is not required for the typical gamma-relaxation of polycarbon ate at low temperature. Consequently, the polymer chain can get its mo bility only from the flexibility of the carbonate linkage. It was also found that the width of the gamma-relaxation peak in the SBI copolyca rbonates decreases systematically with increasing spiro content. This means that in the rather broad peak in BA-PC there is a contribution o f a second damping mechanism at the higher temperature side which is a ffected by the spiro linkage. That damping contribution is therefore a scribed to the phenyl motion. This also explains why the gamma-relaxat ion of polycarbonates with ortho-substituted phenyls occurs at much hi gher temperatures. There the carbonate motion couples to the phenyl mo tion due to sterical hindrance, which is not the case in SRI-PC.