High pressure copolymerization of styrene onto polyethylene

MARTINI, RAQUEL EVANGELINA; BRIGNOLE, ESTEBAN ALBERTO; BARBOSA, SILVIA ELENA

Cancún. México

Congreso; XVI International Materials Research Congress; 2007

NACE - Academia Mexicana de Ciencia de los Materiales

The use of near and supercritical fluids, as solvent aid in polymer processing and polymer chemistry, has been incremented from the last decade. They can have gas-like diffusivities, which have important implications for reaction kinetics, as well as liquid-like densities, allowing solvation of many compounds [1]. On the other hand, macromonomer cationic copolymerization is a growing field of synthetic polymer chemistry [2]. Friedel-Crafts alkylation involves the alkylation of an aromatic ring and an alkyl halide using a strong Lewis acid catalyst. It can be applied to obtain a copolymer from an aromatic monomer and polyethylene (PE) chains as a macromonomer. In the present work a novel method of copolymerization is proposed. Near critical n-heptane is used as reaction medium and swelling agent for the copolymerization of PE with styrene monomer using AlCl3 as catalyst. The reaction was performed in a stirred batch reactor at 140 oC and 150 bar. It was determined that PE is completely solubilized in the n-heptane at high pressure-high temperature conditions [3]. In this way, it is expected that using near critical n-heptane as reaction medium, PE chains and the catalyst will be more available to react each other. The copolymerization reaction was corroborated analyzing the reaction products after a careful pure polystyrene separation by selective soxhlet extraction using tetrahydrofuran. The copolymer obtained was characterized and polystyrene grafted quantified by a combination of techniques like nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The final reaction product morphology was analyzed by scanning electron microscopy (SEM). The effect of the amount of catalyst added was studied varying the content from 1 to 5-wt% of AlCl3 on the same PE/styrene relation. It was found that the highest the catalyst content, the highest the polystyrene grafted. [1] KENDALL, J.L.; CANELAS, J.L; YOUNG, J.L.; DeSIMONE, J.M. Chem. Rev., 99, 543, 1999. [2] KENNEDY J.P.; MARECHAL E. Carbocationic Polymerization, John Wiley Sons, New York, 1999. [3] BARBOSA, S., DÍAZ, M., MABE, G., BRIGNOLE, E., CAPIATI, N., J Polym. Sci. Polym. Phys, 43, 2361, 2005.