Cross-Linking of Polypropylene via the Diels–Alder Reaction

Abstract

In this work, the possibility of preparing cross-linked polypropylene (PP) via Diels–Alder (DA) chemistry is explored. The overall strategy involves reaction of maleated polypropylene (the starting material), furfuryl amine (FFA), and bismaleimide (BM) as the cross-linking agent. The occurrence of reversible cross-linking was studied by checking the presence of relevant peaks in FTIR spectra, i.e., CH out-of-plane bending vibrations of the furan ring’s peak (γCH) at an absorption band of 730–734 cm−1, CH=CH of the BM aromatic ring’s stretching vibrations (υCH=CH) at an absorption band of 1510 cm−1, and the DA adduct (C-O-C, δDAring) at an absorption band of 1186 cm−1 . In agreement with the spectroscopic characterization, the presence of a cross-linked network is also confirmed by rheology, namely the higher storage modulus (G′ ) compared with loss modulus (G′ ′ ) value (G′ >> G′ ′ ), as obtained via temperature sweep. Both the maleic anhydride (MA) content as well as the annealing temperature (50◦ C and 120◦ C) favor the DA reaction, while only partial de-cross-linking (retro DA) is observed at the higher temperature range of 150–200◦ C. In addition, the products show higher mechanical robustness and thermal stability compared to the starting material.