Design of new styrene enriched polyethylenes via coordination copolymerization of ethylene with mono- or alpha,omega-difunctional polystyrene macromonomers
Résumé
omega-Allyl, omega-undecenyl and alpha,omega-undecenyl polystyrene macromonomers, well defined in molar mass and functionality, were synthesized via anionic polymerization. Their coordination copolymerization with ethylene with a cationic alpha-diiimine palladium catalyst [(ArN=C(Me)-C(Me)=NAr)Pd(CH2)(3)(COOMe)]+BAr4/-,-, (Ar=2,6-Pr-i(2)-C6H3 and Ar-i=3,5-(CF3)(2)-C6H3) affords access to a new type of graft copolymers constituted of a polyethylene backbone and polystyrene grafts. It was shown that the environment of the terminal double bond of the PS macromonomers has a huge influence on the polymerization behavior. Indeed, an undecenyl end-group is more reactive than an all I end-group. The copolymerization of ethylene with a,W-Undecenyl polystyrene macrornonomers lead to cross-linking for long polymerization time (18 h at 25 degrees C). The influence of several parameters (polymerization temperature. ethylene pressure, concentration) on molar masses and macromonomer incorporation yield was also investigated. Macromonomers having the lowest molar masses were the most reactive. The molar mass of the copolymer increased with ethylene pressure. As expected with Such a chain walking catalyst, the copolymers presented moderately branched to highly branched structures depending on the ethylene pressure. like for the homopolymerization of ethylene. Finally, rheological investigations of the copolymers showed that a few percentage of polystyrene incorporation can change drastically the mechanical properties of the materials