Influence of flexible segment length on the phase structure and properties of poly(hexamethylene 2,5‐furandicarboxylate)‐block‐biopolytetrahydrofuran copolymers

Abstract

Two series of biobased poly(ether‐ester)s comprised of poly(hexamethylene 2,5‐furandicarboxylate) (PHF) as the rigid segments and biopolytetrahydrofuran (pTHF) with different molecular masses (1000 and 2000 g/mol) as the flexible segments were synthesized employing polycondensation in the molten state. The study mainly focuses on comparing these two series in terms of the length of the flexible segment. The content of pTHF segments in the copolymer chains varied from 25 to 75 wt.%. The molecular structure and composition, phase structure, and thermal and mechanical properties were characterized by nuclear magnetic resonance (1H NMR) and Fourier‐transformed infrared (FTIR) spectroscopies, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and positron annihilation lifetime spectroscopy (PALS). In addition, mechanical performance and thermo‐oxidative and thermal stability have been investigated. Moreover, cyclic tensile properties were studied to evaluate the elastic properties. 1H NMR and FTIR spectroscopies demonstrate that the syntheses were correctly carried out, which made it possible to obtain the desired compositions of the block copolymers with high molecular masses. The decrease in Tm1, Tc1, and XcPHF values was visible, along with the increase in the flexible segment content. Moreover, the characteristic properties measured by PALS and the values of temperatures designated from TGA (inert and oxidizing atmosphere) did not vary between copolymer series PHF‐b‐F‐pTHF1000 and PHF‐b‐F‐pTHF2000. In turn, along with an increase in flexible segment content and the length of the pTHF, the values of tensile modulus, stress at break, and hardness decrease, while the value of elongation at break increases.