Poly(propylene terephthalate) containing 4,4-sulfonylbisphenol units:effect of chemical composition on the physical-chemical properties

Copolyesters containing rigid aromatic units based on 4,4'-sulfonylbisphenol (bisphenol S) have been prepared by melt mixing poly(propylene terephthalate) (PPT) with an ethoxylated bisphenol S (sulfonyldiphenol). The insertion of the bisphenol units inside the polymer chain occurred quantitatively and no side reaction has been observed. The copolymers displayed good thermal stability. The main effect of copolymerization was a lowering in the degree of crystallinity and a decrease of the melting temperature with respect to PPT. On the contrary, an increment of T-g as the content of bisphenol S units increased due to the stiffening effect of the moieties deriving from bisphenol S. The Wood equation described well the correlation between T-g and composition.