Functionalized multi-walled carbon nanotubes with stereospecific Ziegler-Natta catalyst species: Towards facile in situ preparation of polypropylene nanocomposites

Abstract

Multi-walled carbon nanotubes (MWCNTs) were functionalized with a stereospecific Ziegler-Natta catalyst species for in situ preparation of polypropylene (PP)/MWCNT nanocomposites. The functionalization process involved initially treating MWCNTs containing a few (∼3.0% w/w) surface hydroxyl groups (MWCNT-OH) with an excess amount of Grignard reagent followed by further reaction with TiCl4. Triethylaluminum (TEA) and dimethoxydiphenylsilane (DDS) were used as co-catalyst and external electron donor, respectively. The resulting MWCNTs (MWCNT/Mg/Ti) only behaved as a fair isospecific Ziegler-Natta catalyst, promoting propylene polymerization at a moderate rate and resulting in PP with moderate isotacticity indices (76.4–91.0%). To improve the catalytic performance, the electron-donating reagent 9,9-bis(methoxymethyl)fluorine (BMMF) was added into the MWCNT functionalization process, incorporating BMMF into the catalytic material and simultaneously reducing the quantity of TiCl4 immobilization. The BMMF-incorporated functionalized MWCNTs (MWCNT/Mg/BMMF/Ti) produced PP with a high isotacticity index (92.0%) without the use of an external electron donor. PP with an isotacticity index greater than 98% was achieved when DDS was used as external electron donor during the polymerization process.