Graft chain propagation rate coefficients of acrylic acid in melt graft copolymerization with linear low density polyethylene

Abstract

Graft chain propagation rate coefficients ( k p,g) for grafting AA onto linear low density polyethylene (LLDPE) in the melt in ESR tubes have been measured via Fourier transform infrared (FTIR) spectroscopy and electron spin resonance (ESR) spectroscopy in the temperature range from 130 to 170 °C. To exclude the effect of homopolymerization on the grafting, the LLDPE was pre-irradiated in the air by electron beam to generate the peroxides and then treated with iodide solution to eliminating one kind of peroxides, hydroperoxide. The monomer conversion is determined by FTIR and the chain propagation free-radical concentration is deduced from the double integration of the well-resolved ESR spectra, consisting nine lines in the melt. The temperature dependence of k p,g is expressed: ln [ k p,g g mol − 1 s − 1 ] = ( 26.2 ± 0.22 ) − ( 3876.9 ± 92.8 ) ( T K ) − 1 . The magnitude of k p,g from FTIR and ESR analysis is in good agreement with the theoretical data deduced from ethylene-AA copolymerization, suggesting this method could reliably and directly provide the propagation rate coefficient. The comparison of k p,g with the data extrapolated from solution polymerization at modest temperature indicates that the extrapolated data might not be entirely fitting to discuss the kinetics behavior in the melt.