Poly(propylene terephthalate) modified with 2,2-Bis[4-(ethylenoxy)-1,4-phenylene]propane terephthalate units: Thermal behavior, crystallization kinetics and morphology.

The thermal behavior of poly(propylene terephthalate) modified with 2,2-bis[4-(ethylenoxy)-1,4-phenylene]propane terephthalate units (PPT/BHEEBT copolymers) was investigated by thermogravimetric anal. (TGA), DSC and hot-stage optical microscopy (MO). Good thermal stability was found for each sample. The thermal anal. carried out using the DSC technique showed that the Tm of the copolymers decreased with the increment in BHEEBT unit content. This was different from the Tg which, on the contrary, increased. Wide-angle X-ray diffraction measurements allowed the identification of the PPT cryst. structure in each semicryst. sample. Multiple endotherms were shown in the PPT/BHEEBT samples, due to melting and recrystn. processes, similarly to PPT. The T°m of the copolymers was derived from the application of the Hoffman-Weeks' method. The isothermal crystn. kinetics were analyzed according to Avrami's treatment. The introduction of BHEEBT units was found to decrease the crystn. rate compared to pure PPT. Values of the Avrami's exponent n close to 3 were obtained for PPT/BHEEBT6 and PPT/BHEEBT12, regardless of Tc, in agreement with a crystn. process originating from pre-detd. nuclei and characterized by three-dimensional spherulitic growth. For these two copolymers, space-filling spherulites were obsd. through optical microscopy at all Tcs. The heat of fusion (_Hm) was correlated to the sp. heat increment (_cp) for samples with different degrees of crystallinity, and the results were interpreted on the basis of the existence of an interphase, whose amt. was found to depend mainly on compn., despite the thermal treatment applied to the polymer also playing an important role.