EFFECT OF ETHYLENE CONTENT ON MALEIC ANHYDRIDE-GRAFTED POLYPROPYLENE BASED BLOCK COPOLYMERS

This paper reports an alternative approach by incorporating ethylene segments into polypropylene backbone, that is, ethylene propylene (EP)/isotactic polypropylene (iPP) block copolymers, to mitigate the chain scission issue during the free radical initiated maleic anhydride (MAH)-grafting reactive extrusion of polypropylene. C-labeled MAH was used to study chemoselectivity by C Nuclear Magnetic Resonance (NMR) spectroscopy. Results showed that MAH was selectively grafted onto ethylene sites of copolymers. The MAH-grafting reactive extrusion conducted on a 25-mm twin-screw extruder indicated that increasing ethylene contents in EP/iPP block copolymers from 15 wt% to 46 wt% not only significantly improved MAH-grafting efficiency but also dramatically reduced the molecular weight degradation and low molecular weight fraction in the resultant functionalized polymers. This method can be also leveraged to other free radical-based functional polypropylenes.