Synthesis and properties of isocyanate-functionalized isosorbide high heat-resistant copolyesters

Abstract

In this work, conventional poly(ethylene glycol-1,4-cyclohexanedimethanol terephthalate) (PCTG) was modified by functionalizing isosorbide (ISB) with isophorone diisocyanate (IPDI). The structural, crystallographic, thermal and mechanical properties of PCTG copolyesters modified with IPDI-functionalized ISB were comprehensively characterized using Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (¹H NMR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), heat deflection temperature (HDT), and mechanical testing. By comparing with PCTG copolyesters modified by directly incorporating ISB or 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO), the advantages of PCTG copolyesters modified with functionalized ISB were highlighted. Thermal analysis revealed that the PCTG copolyester modified with functionalized ISB exhibited good thermal stability with an initial decomposition temperature of 404.4 °C, along with a glass transition temperature (T_g) of 110.6 °C and a heat deflection temperature of 89.8 °C. These values are significantly higher than those of the copolyester modified by directly incorporating ISB, demonstrating its superior heat resistance. Furthermore, the PCTG copolyester modified with functionalized ISB exhibited a tensile strength of 27.4 MPa, an impact strength of 16.9 MPa, and the highest bending strength of 52.5 MPa. These results demonstrate that the high heat-resistant copolyester synthesized using IPDI-functionalized ISB possesses excellent overall properties, comparable to those of the CBDO-modified PCTG copolyester. These findings also provide valuable guidance for the synthesis of isocyanate-functionalized isosorbide-based copolyesters with exceptional thermal properties and tunable mechanical and crystalline characteristics.