Thermal decomposition kinetics of liquid crystalline p-oxybenzoate/ethylene terephthalate/third monomer terpolymers

Abstract

The thermal stability and decomposition kinetics of two series of thermotropic liquid crystalline terpolymers consisting of p-oxybenzoate, ethylene terephthalate and third monomer unit including vanillate or phenylene terephthalate with several monomer ratios have been studied using dynamic thermogravimetry (TG) based on three single heating rate methods of kinetic analysis. The results indicate that the thermal stability and degradation kinetics of the terpolymers are dependent of monomer ratio, third monomer content, heating rate, test atmosphere, measuring method, and calculating method. The rigidity of p-oxybenzoate appears to be responsible for the improved the rmostability and resistance of main-chain scission in the terpolymers. Less p-oxybenzoate- or third monomer-containing terpolymers seem to exhibit larger activation energy, frequency factor, maximum decomposition rate and lifetime, but smaller decomposition order of thermal decomposition. The maximum degradation rate of the terpolymers increases linearly with increasing heating rate. The activation energy, preexponential factor, and decomposition order for the first stage thermal decomposition of the p-oxybenzoatelethylene terephthalate/vanillate terpolymers under nitrogen range between 217 and 260 kJ/mol, 35 and 43 min −1, and 3.1 and 4.7, respectively, which are larger than the three kinetic parameters of the thermal degradation for the p-oxybenzoate/ethylene terephthalate/phenylene terephthalate terpolymers under air. The longest estimated lifetimes of the terpolymers are 59.1 min at 350°C and 1.1 min at 410°C.