Thermal decomposition kinetics and dielectric properties of polyurethane grafted onto PEMA-co-PHEMA

Abstract

Segmented polyurethane (PU) was synthesized via grafting from PEMA-co-PHEMA. This polyurethane was characterized by experimental measurements such as FTIR, 1H NMR, thermogravimetric analysis (TGA) and DSC techniques. The degradation process reaction mechanism and the kinetic parameters about the polyurethane grafted onto PEMA-co-PHEMA in nitrogen environment were examined by TGA at varied heating rates. The activation energies of thermal degradation for polyurethane by the Kissinger, Flynn–Wall–Ozawa and Tang methods, without knowing the reaction mechanism (RM), were found to be 173.65, 173.85 and 163.38 kJ/mol, respectively. According to dynamic measurements, the analysis of every process mechanism of Coats–Redfern and Van Krevelen methods demonstrated that the most likely model for the decomposition process of polyurethane complies with the three-dimensional diffusion, D3 mechanism. Analysis of the experimental results proposed that the reaction mechanism in the conversion range (2–50%) was a D3 [three-dimensional diffusion (Jander equation)] deceleration type. The dielectric properties of polyurethane were measured at varied frequencies at room temperature. The capacitance measurements were carried out at room temperature over the frequency range 1–10,000 kHz. Conductivity σ* and the real and imaginary parts of the dielectric permittivity e* were obtained for PEMA-co-PHEMA-g-PCL with soft segment of PU, and PEMA-co-PHEMA-g-PU. The dielectric constant of all samples decreased as the frequency increased.