Synthesis, structure, and physical properties of poly(trimethylene terephthalate)‐block‐poly(caprolactone) copolymers

Abstract

ABSTRACTThe series of poly(trimethylene terephthalate)‐block‐PCLT (PTT‐block‐PCLT) copolymers with different contents of PTT as rigid, and poly(caprolactone) (PCL) as flexible segments have been synthesized from dimethyl terephthalate (DMT), 1,3‐bio‐propanediol, and PCL diol) in a two‐step process involving transesterification and polycondensation in the melt. The weight amount of flexible PCLT segments varied from 0 (homopolymer PTT), 25, 35 to 45%. The molecular structure of the synthesized copolymers was confirmed by nuclear magnetic resonance and Fourier transform infrared spectroscopy analyses. According to Hoy's method, one confirmed that PTT and PCL are likely miscible, as the difference of the solubility parameters of PTT and PCL block pairs, equals to 3.15 MPa1/2. Moreover, the phase structure and mutual miscibility for the series of PTT‐block‐PCLT copolymers was characterized by differential scanning calorimetry, dynamic mechanical thermal analysis, and wide‐angle X‐ray scattering measurements. In copolymers with 35 and 45 wt % of flexible segments, the crystalline phase is formed during annealing above glass‐transition temperature of copolymer. These copolymers during cooling at the standard rate do not crystallize. It was also found that incorporation of PCLT flexible segments, due to the macrophase separated structure, cause the decrease of the melting point and glass‐transition temperature, along with the tensile modulus and tensile strength of PTT‐block‐PCLT copolymers, and at the same time cause an increase in the value of the elongation at break. As a result of copolymerization of PTT with PCLT, one obtained multiblock copolymers with a heterophase structure. By changing the PTT/PCLT ratio, one obtained copolymers that differ in hardness and tensile strength. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47341.