Effect of stereo-defects distribution on rheological behavior of isotactic polypropylene
writer：Tong Wu, Feng Yang, Jian Kang, Ya Cao, Ming Xiang.
keywords：rheological behavior
source：期刊
specific source：Journal of Macromolecular Science Part B: Physics. 51(9):1838-1850, 2012.
Issue time：2012年
A series of five isotactic polypropylenes (iPP) used commercially for producing biaxial oriented polypropylene film (BOPP), which had similar average degrees of isotacticity but different stereodefects distribution, was studied. Xylene solubles (XS) at different temperatures and high temperature solution 13C NMR were used to characterize the stereodefects distribution of the five samples. These samples gradually became more random following the order of sample A to E. The plateau modulus (G0N ≈ 0.2 MPa at 190?C) of these samples was lower than those of metallocene-catalyzed polypropylenes with very narrow molecular weight distributions (MWD) (G0N ≈ 0.4 MPa at 190?C), indicating that the influence of MWD on G0N cannot be neglected. The storage mod- ulus and complex viscosity of the five samples decreased gradually with the widened stereodefects distribution, due to the formation of a less constrained network that fi- nally caused the reduction of G0N and the increase of the flow activation energy. The rheological behavior of the BOPP resin samples could be well related to the results of XS and 13C NMR, implying that the rheological measurement can be adopted as a simple and efficient method to characterize the stereodefects distribution of isotactic polypropylene.