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Poly(butylene cyclohexanedicarboxylate/diglycolate) random copolymers (P(BCEmBDGn)) of various compositions were synthesized and characterized from the molecular, thermal, structural, and mechanical point of view. Barrier properties to different gases (oxygen and carbon dioxide) were also evaluated. All the polymers showed good thermal stability and appeared as semicrystalline materials at room temperature. The main effect of copolymerization was a lowering in the crystallinity and a decrease of T m with respect to homopolymers. The dependence of T m on composition for copolymers with high butylene cyclohexanedicarboxylate unit content was well described by Baur’s equation. X-ray diffraction (XRD) measurements indicated that two different crystalline phases are present, depending on composition: copolymers with high BCE unit content were characterized by PBCE crystal phase, whereas those rich in BDG counits crystallized in PBDG lattice. The samples displayed different surface hydrophilicity: the water contact angle regularly decreased with the increasing mol % of BDG. The mechanical properties were found strictly related to crystallinity degree (χc); the copolymers containing 60–75 mol % of BDG showed the lowest elastic modulus and the highest elongation at break. Lastly, the chemical composition of the copolymer strongly influenced permeability to CO2 and O2. Moreover, the selectivity ratios for the examined samples increased with the increasing of BDG mol %, confirming the existence of a correlation between the permeability and the chemical composition. Almost all copolymers showed improved barrier properties with respect to polylactide films tested under the same conditions.

Crystallization kinetics and melting behaviour of poly(propylene terephthalate) (PPT) were investigated by means of differential scanning calorimetry and hot-stage optical microscopy. Isothermal crystallization kinetics was analysed according to the Avrami treatment. The effects of temperature and duration of melting on the overall rate of isothermal crystallization were studied: the rate was found to decrease with increasing melting temperature and melting time. This result was discussed on the basis of the gradual destruction of predetermined athermal nuclei. Values of the Avrami exponent close to 3 were obtained, regardless of the adopted thermal treatment and the crystallization temperature, T c , in agreement with a crystallization process originating from predetermined nuclei and characterized by three-dimensional spherulitic growth. As a matter of fact, spacefilling spherulites were observed by optical microscopy at all T c 's, independent of the applied thermal treatments. For each of them, the rate of crystallization became lower as T c increased, as usual at low undercooling where the crystallization process is controlled by nucleation. The observed multiple endotherms, which are commonly displayed by polyesters, were influenced by T c and ascribed to melting and recrystallization processes. Linear and non-linear treatments were applied in order to estimate the equilibrium melting temperature for PPT, by using the corrected melting temperatures. The non-linear estimation yielded an about 33°C higher value with respect to the one obtained by means of the linear approach. Through the analysis of secondary nucleation theory, the classical II→III transition was found to occur at a temperature of 194°C. The average work of chain folding for nucleation was determined to be c. 5.2 kcal/mol. The heat of fusion was correlated to the specific heat increment for samples with different degree of crystallinity and the results were interpreted on the basis of the existence of an interphase, whose amount was found to depend on the thermal treatment the polymer was subjected to.

Poly(propylene/neopenthyl terephthalate) random copolymers (PPT-PNT) and poly(neopenthyl terephthalate) (PNT) were synthesized and subjected to molecular characterization. Afterwards, the polyesters were examined by TGA, DSC, and X-ray. The copolymers, which displayed a good thermal stability, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PPT. XRD measurements allowed the identification of the PPT crystalline structure in all cases. Amorphous samples were obtained after melt quenching, with the exception of PPT-PNT5, and an increment of T g as the content of NT units is increased was observed due to the effect of the side methylene groups in the polymeric chain. The Wood equation described well T g -composition data. Lastly, the presence of a rigid-amorphous phase was evidenced in the copolymers, whose amount depended on composition and on thermal treatment.