UV Aging of Isotactic Polypropylene Functionalized with Carbazole Groups

Carbazole group functionalized isotactic polypropylene (P-C) samples were prepared via direct copolymerization of propylene and alpha-olefin bearing terminal carbazole group. The carbazole group could absorb ultraviolet light and exibibit blue-purple luminescence under 365 nm ultraviolet light, which may endows the material with anti-photooxygen aging property. C-13-NMR data showed that the propylene/11-carbazole-1-undecene copolymer(P-Cs) have high tacticity. In order to maintain the excellent mechanical properties of isotactic polypropylene, the incorporation of comonomer was controlled at 0.45 mol%-1.67 mol%. The P-C samples with different carbazole group contents were studied via UV aging and the UV-oxidative stability tests. After the same aging time, when large and deep cracks were observed on the surface of the iPP sample, only the P-C1 sample with the lowest carbazole group content showed small cracks on the surface, while the P-C2 and P-C3 samples with higher content of carbazole groups had no cracks. Tensile tests revealed that losses in tensile properties of the P-C samples were far less compared to that of the pure iPP sample. At 120 h, the mechanical properties of the iPP samples were completely lost. Under the same conditions, the tensile strength of the P-C1 samples remained above 98%, and the tensile strengths of the P-C2 and P-C3 samples were significantly improved. The DSC data showed that the melting temperature (T-m) of the iPP samples decreased by 7 degrees C after UV irradiation, while the T-m of the samples in the P-C group decreased by at most 2 degrees C. which indicated that the introduction of carbazole groups could stabilize the thermal properties of the samples under UV irradiation. GPC test results showed that the thermal properties and molecular weghts of polypropylenes with carbazole group were well maintained after the UV aging process, and that the degradation reaction has been significantly inhibited. In conclusion, the introduction of carbazole groups could effectively enhance the UV-oxidative stability of polypropylene. [GRAPHICS] .