13C NMR Study of the Grafting of Maleic Anhydride onto Polyethene, Polypropene, and Ethene−Propene Copolymers

The reaction products from the radically initiated grafting of specifically 13C-enriched maleic anhydride ([2,3-13C2]MA) onto polyethene, isotactic polypropene and ethene-propene copolymers in the melt and in solution are investigated using noise-decoupled and 1D inadequate 13C NMR spectroscopy. The sites of attachment and the structures of the grafts depend on (co)polymer composition. In random EPM, MA attaches to methylene and methine carbons in the backbone. In alternating EPM, MA attaches solely to polymer methines, indicating that (CH2) m sequences with m > 3 are needed for MA attachment to backbone methylene carbons. In the copolymers and in IPP, grafts are single succinic anhydride rings; in HDPE and LDPE short MA oligomers are also present. In polyolefins containing polypropene sequences, chain scission can yield structures in which the anhydride ring is attached to the chain terminus via a fully substituted double bond.