Rheological and thermal degradation properties of hyperbranched polyisoprene prepared by anionic polymerisation

Rheological and thermal degradation properties of hyperbranched polyisoprene prepared by anionic polymerisation

Habibu, Shehu 1 ; Muhamad Sarih, Norazilawati1 ; Sairi, Nor Asrina1 ; Zulkifli, Muzafar 2

Published Nov 11, 2019 on Dryad. https://doi.org/10.5061/dryad.0cfxpnvx2

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Abstract

Hyperbranched polyisoprene was prepared by anionic copolymerisation under high vacuum condition. Size exclusion chromatography (SEC) was used to characterise the molecular weight and branching nature of these polymers. The characterisation by differential scanning calorimetry (DSC) and melt rheology indicated lower T_g and complex viscosity in the branched polymers as compared to the linear polymer. Degradation kinetics of these polymers was explored using thermogravimetric analysis (TGA) via non-isothermal techniques. The polymers were heated under nitrogen from ambient temperature to 600 °C using heating rates from 2, to 15 °C min^-1. Three kinetics methods namely Friedman, Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) were used to evaluate the dependence of activation energy (E_a) on conversion (α). The hyperbranched polyisoprene decomposed via multistep mechanism as manifested by the nonlinear relationship between α and E_a while the linear polymer exhibited a decline in E_a at higher conversions. The average E_a values range from 258 to 330 kJmol^-1 for the linear, and 260 to 320 kJmol^-1 for the branched polymers. The thermal degradation of the polymers studied involved one-dimensional diffusion mechanism as determined by Coats–Redfern method. This study may help in understanding the effect of branching on the rheological and decomposition kinetics of polyisoprene.