Type of Document Thesis Author kotha, sushmitha reddy Author's Email Address firstname.lastname@example.org URN etd-11212005-160637 Title Statistical Analysis of the Stereo Defect Sequence Distribution of Ziegler-Natta Isotactic Poly (Propylene) in Light of the Crystallization Behavior of its Citref Fractions Degree Master of Science Department Chemical Engineering, Department of Advisory Committee
Advisor Name Title Rufina G. Alamo Committee Chair John C. Telotte Committee Member Ravidran Chella Committee Member Keywords
Date of Defense 2005-11-18 Availability unrestricted AbstractThe inter and intramolecular distribution of defects of a Ziegler-Natta isotactic poly(propylene) (ZN-ipp) were inferred from the GPC, 13C NMR defect characterization, crystallization and polymorphic behavior of its fractions separated by isotacticiy. The NMR results confirmed this type of fractionation. The defect composition decreased from fraction 1 to fraction 9 indicating a non-uniform intermolecular defect distribution in the ZN-ipp chains. The linear growth rates of these fractions are basically the same, within experimental error, irrespective of their defect composition, which varied from 0.25 mol% to 1.28 mol% among the nine fractions. In addition, even the most defected fractions are observed to have very low contents of gamma phase. All these results indicate that the intra-molecular distribution of defects in the ZN-ipp fractions deviates from the random type of defect distribution. In contrast to the linear growth rates, the observed overall crystallization rates correlate with isotacticity content and with nucleation density.
The observed 13C NMR pentad/heptad stereo sequences for the parent and the ZN-ipp fractions were analyzed with two and three state statistical models. The results were discussed in light of the observed fractionation and crystallization behaviors of the ZN-ipp fractions. Sequence distribution curves and probability parameters predicted by a modified three state model Es/C1/CE1 satisfies, for the parent and all the fractions their observed crystallization behavior. This result indicates that all the ZN-ipp fractions consist of three types of stereo sequences: long highly isotactic stereo sequences produced by the enantiomorphic site control state, isotactic stereo-sequences produced by the chain end site control state, and weakly isotactic, stereoblock sequences produced through the C1 switching state. Blocky defected sequences, including syndiotactic stereodefects, are predicted with the C1 state. Only, the fractional amount of each component varies among all the fractions.
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