the relationship among changes in microstructure, active sites behavior and properties in the propylene polymerization with a 4th generation ziegler-natta catalyst

Three polypropylene samples (1-3) were synthesized with a 4th generation ziegler-natta catalyst in the presence of cyclohexyldimethoxymethylsilane (donor c), dicyclopenthyldimethoxysilane (donor d) and diisopropyldimethoxysilane (donor p), respectively, as external electron donors. the physical properties of the synthesized polypropylenes were determined. for samples 1 to 3, successive self-nucleation and annealing (ssa) and fourier transform infrared spectroscopy (ft-ir) analyses indicated that the relative content of the fraction with high isotacticity and regularity in conformational structure decreased in contrast with the fraction of low isotacticity and low uniformity in stereo-defect distribution from sample 1 to 3. the results demonstrated that the longer the isotactic sequence length and the less uniform the stereo-defect distribution, the greater the conformational order. deconvolution of the molecular weight distribution curves indicated that the stability of the active centers increased from samples 1 through 3, but the participation of stereospecific active centers in the polymerization decreased. dma tests showed that samples 3 and 1 had the highest damping ability and storage modulus, respectively.