Abstract: In this work, the macromolecular peroxide-induced grafting of MAA onto LLDPE by reactive extrusion was chosen as model system to study the apparent chain propagation rate coefficients for both graft reaction(k_p,g) and homopolymerization of grafting monomers(k_p,h). The time-evolution rates of graft copolymerization and homopolymerization both exhibited two stages, linear and flat stage, which were controlled by monomer solubility and diffusion. By measuring the concentration of free-radicals and initial polymerization rate, which were determined with electron spin resonance spectroscopy(ESR) and Fourier transform infrared spectroscopy(FTIR), k_p,g and k_p,h were obtained. It was found that k_p,g increased with increasing temperature, while k_p,h decreased when the temperature was over 200 ℃, this has been attributed to the effect of ceiling temperature. That the value of k_p,h was always larger than k_p,g was also observed, indicating that graft copolymerization was not dominant reaction in this grafting process. The measured data were in agreement with theoretical calculations, which showed that this technique reliably and directly provides individually apparent chain propagation rate coefficients.

Key words: Reactive extrusion, Linear low density polyethylene, Methyacrylic acid, Apparent graft chain propagation rate contant