Cross-Linking of Polypropylene via the Diels-Alder Reaction

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 (gamma CH) at an absorption band of 730-734 cm(-1), CH=CH of the BM aromatic ring's stretching vibrations (upsilon CH=CH) at an absorption band of 1510 cm(-1), and the DA adduct (C-O-C, delta DAring) 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 degrees C and 120 degrees C) favor the DA reaction, while only partial de-cross-linking (retro DA) is observed at the higher temperature range of 150-200 degrees C. In addition, the products show higher mechanical robustness and thermal stability compared to the starting material.

Automated summary

This work investigates the preparation of cross-linked polypropylene (PP) through Diels-Alder (DA) chemistry. The study confirms the occurrence of reversible cross-linking and the formation of a cross-linked network using spectroscopic characterization and rheology. Additionally, the cross-linked PP exhibits higher mechanical strength and thermal stability.