Synthesis of poly(alkylene succinate) biodegradable polyesters, Part II: Mathematical modelling of the polycondensation reaction

In this investigation, synthesis of three biodegradable aliphatic polyesters, namely poly(ethylene succinate) (PESu), poly(propylene succinate) (PPSu) and poly(butylene succinate) (PBSu), is presented using the appropriate diols and succinic acid in the presence of tetrabutoxytitanium as catalyst. A theoretical mathematical model for the polycondensation reaction is developed and applied successfully in the simulation of all experimental data. From measurements of intrinsic viscosity (IV) at four polycondensation temperatures (210, 220, 230 and 245 °C) and different times from 15 min to 3 h, it was concluded that PESu exhibits higher values followed by PBSu and finally PPSu. Using additional measurements on the carboxyl content and the simulation model results, it was found that when ethylene glycol is used as reactant, both esterification and transesterification reaction rates are promoted resulting thus in lower carboxyl concentrations and higher IV values. However, the transesterification reaction rate constant of PPSu is much lower compared to PBSu leading to higher carboxyl and hydroxyl end groups and therefore finally lower IV values. Moreover, the esterification rate constant was estimated always to be much larger compared to the rate constant of the transesterification reaction, meaning that the former reaction proceeds much faster compared to the later, resulting thus in very low values of the carboxyl end groups compared to corresponding hydroxyl end groups. Finally, from measurements of the mechanical properties of the polyesters produced it was found that concerning the tensile strength and the elongation at break, PBSu exhibits the larger values followed by PESu in the order: PBSu > PESu > PPSu, whereas PESu exhibits higher Young's Modulus in the order: PESu > PBSu > PPSu.