Castor Oil and HER Based Polyurethanes: Synthesis, Characterization and Structure-Thermal Stability Relation

Polyurethanes (PUs) were prepared from solvent and catalyst free reaction mixture containing polyethylene glycol (PEG), 4,4’-methylene diphenyl diisocyanate (MDI) and 1,3-bis(2-hydroxyethoxy) benzene (HER) and/or castor oil (CAO). PUs were characterized using the Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopic methods. Thermal studies on PUs using differential scanning calorimetric (DSC) and thermogravimetric analysis coupled with FTIR (TG/FTIR) proved that CAO-extended PUs were thermally more stable than HER extended PUs. The partial and complete replacement of HER content in PUs using CAO enhanced the thermal stability by shifting degradation temperature to higher temperature (5-15 ℃) and enhancing the char residue. The parameters derived from DSC traces, thermogram and differential thermogram confirmed that PUs synthesized using PEG 1500 are thermally more stable than the PUs prepared using PEG 4000. The probable degradation mechanism to study the role of β-hydrogen on the thermal stability was proposed and discussed based on the results of TG/FTIR.