Synthesis, Characterization and Thermal Degradation Kinetics of a New Pyrazole Derived Methacrylate Polymer, Poly(1,3-Diphenyl-1H-Pyrazol-5-Yl Methacrylate)

Abstract

Since the behavior and properties of macromolecular pyrazole derived polymers differ from their small molecules, such polymers are in the class of well-defined functional polymers due to the fact that the pyrazole ring contains two π-bonds as well as two hetero atoms in its structure, and this feature makes them important in the fields of scientific and technological applications. In present study, therefore, we synthesized a new pyrazole derived methacrylate monomer, 1,3-diphenyl-1H-pyrazol-5-yl methacrylate, from the reaction of 1,3-diphenyl-5-pyrazolone with methacryloyl chloride in the presence of triethylamine. After that, its homopolymerization was carried out by free radical polymerization method at 60 °C initiated with benzoyl peroxide. Spectral characterizations were achieved by 1H-NMR and FTIR spectroscopies. The kinetics of thermal degradation of the new polymer, poly(1,3-diphenyl-1H-pyrazol-5-yl methacrylate), poly(DPPMA), were investigated by thermogravimetric analysis (TGA) at different heating rates. The initial decomposition temperature of the polymer changed from 216.3 °C to 243.5 °C depending on the increasing heating rate. The thermal decomposition activation energies in a conversion range of 7–19% were 79.45 kJ/mol and 81.56 kJ/mol by the Flynn– Wall–Ozawa and Kissinger methods, respectively. Thermodegradation mechanism of the poly(DPPMA) were investigated in detail by using different kinetic methods available in the literature such as Coats-Redfern, Tang, Madhusudanan and Van Krevelen. Among all these methods, the best result was obtained for Coats-Redfern method (E = 90.93 kJ/mol) at the optimum heating rate of 15 °C/min for D1 mechanism that is a one-dimensional diffusion type deceleration mechanism.