Synthesis, curing, and degradation kinetics of polyurethanes based on poly(ethylene glycol), isosorbide, and pentamethylene diisocyanate

Abstract

Polyurethane (PU) synthesis based on poly(ethylene glycol) (PEG) with isosorbide (ISO) and pentamethylene diisocyanate (PDI), named (ISOPUs) was carried out targeting PUs from renewable sources. The cross-linked ISOPUs were produced and the details of the curing kinetics were determined via Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). DSC scans displayed exotherms between 100 and 200°C, related to cross-linking. ISO addition accelerated the curing and the maximum curing rate (Cmax), with 91°C and 0.2964 min−1 for the compound with 70% ISO. FTIR spectra confirmed the interaction between OH (ISO/PEG) and NCO (PDI) groups, with total NCO consumption (band at 2267 cm−1). Through the thermogravimetric analyses (TGA), the PU/70% ISO presented weight loss at 146°C due to the degradation of ISO. ISOPUs displayed a decreased activation energy (Ea) during curing over a range of 100 to 42 kJ/mol for 0 < α < 5%, as demonstrated using the Friedman model, and higher thermal stability as evidenced through TG analyses. Curing and degradation kinetics were modeled using Friedman (FR), Kissinger-Akahira-Sunose (KAS), and Ozawa-Flynn-Wall (OFW). Overall, ISO accelerated the curing rate and increased the degradation Ea, suggesting high thermal stability for PUs with intermediate ISO contents, that is, 30%–50%.