Neopenthyl glycol containing poly(propylene azelate)s: Synthesis and thermal properties

Poly(neopenthyl azelate) (PNAz) and poly(propylene/neopenthyl azelate) random copolymers (PPAz–PNAz) (NAz unit content from 5 to 20 mol%) were synthesized and characterized in terms of chemical structure and molecular weight. Afterwards, the polyesters were examined by TGA, DSC and X-ray diffractometry. Good thermal stability was found for each sample. The thermal analysis showed that the Tm of the copolymers decreased with the increment in NAz unit content, differently from Tg, which on the contrary increased. X-ray diffraction measurements allowed the identification of the PPAz crystalline structure in all the copolymers. Multiple endotherms were shown in the PPAz–PNAz samples, due to melting and recrystallization processes, similarly to PPAz. The Tm∘ of the copolymers was derived from the application of the Hoffman-Weeks’ method. Baur’s equation described well the Tm-composition data. The isothermal crystallization kinetics were analyzed according to Avrami’s treatment. The introduction of NAz units decreased the crystallization rate compared to pure PPAz. Values of the Avrami’s exponent n close to 3 were obtained in all cases, regardless of Tc, in agreement with a crystallization process originating from predeterminated nuclei and characterized by a three dimensional spherulitic growth.