Abstract:

Cross-linking is a commonly used method for polyolefin modification to improve the material's mechanical properties, thermo- and chemical resistance. High molecular mass(M_w) iPPs containing reactive anthracene groups were synthesized by coordination copolymerization. Crosslinked iPP films could be prepared by adding bi-functional N,N'-1,4-phenylene bismaleimide as a crosslinker to react with the pendent anthracene groups during the solvent casting process of the film. The cross-linking degree of the films could be easily tuned by the addition of the crosslinker. Characteristic absorption bands in Fourier transform infrared(FT-IR) spectra of the crosslinked films and gravimetric analysis of the insoluble portion could be used to determine the crosslinking degree. Differential scanning calorimetry(DSC) and wide-angle X-ray diffraction(WAXD) analysis revealed that the crystallinity and crystallization capability of the films decreased followed with the increase of cross-linking degree, which were mainly caused by the restricted chain movement. On the other hand, according to DMA analysis, the loss modulus dropped gradually with the increase of cross-linking degree, indicating the loss of toughness brought by cross-linking. The increased T_g detected from loss angle curves indicated the enhancement of thermoresistance. The tensile stress of the crosslinked iPP films were improved by forming polymer network containing more force bearing point, while the elongation at break dropped drastically because of the chains' poor movability.

Key words: polypropylene, Diels-Alder reaction, crosslinking