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 T_m of the copolymers decreased with the increment in NAz unit content, differently from T_g, 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 of the copolymers was derived from the application of the Hoffman-Weeks’ method. Baur’s equation described well the T_m-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 T_c, in agreement with a crystallization process originating from predeterminated nuclei and characterized by a three dimensional spherulitic growth.