Type of Document Thesis Author Chiari, Ysela L Author's Email Address email@example.com URN etd-06142007-160620 Title NMR Characterization and Isothermal Crystallization of Random Iso-Propylene Copolymers with Ethylene and 1-Octene Co-Units Degree Master of Science Department Chemical Engineering, Department of Advisory Committee
Advisor Name Title Rufina G. Alamo Committee Chair Ravindran Chella Committee Member Sachin Shanbhag Committee Member Keywords
- Propylene Copolymers
- Isothermal Crystallization
- 13C NMR
Date of Defense 2007-06-05 Availability unrestricted AbstractPropylene ethylene and 1-octene copolymers synthesized with the same type of metallocene catalyst were analyzed using 13C solution NMR to determine the microstructure (tacticity, regio-regularity, and concentration of comonomer) and the comonomer sequence distribution. The peak assignments followed published literature.
Propylene ethylene copolymers (PE) show a comonomer content ranging from 7.5 up to 20.8 mol %, and constant stereo and regio defects of 1.3 0.40 mol % and 1.0 0.1 mol % respectively. The propylene 1-octene copolymers (PO) have a comonomer content ranging from 5.9 to 14.9 mol % while the stereo and regio defects, also constant in this series, are 2.4 0.3 mol % and 0.4 0.1 mol % respectively.
A triad distribution analysis of the NMR resonances of sequences pertaining to the comonomer followed the predictions from Bernoullian and first order Markovian distributions for all copolymers. The product of the reactivity ratio was consistent with a random distribution for all copolymers of the series.
A very strong effect of molecular weight on the crystallization kinetics of two PE copolymers with similar ethylene content (~20 mol %) and different molar mass is associated with slow segmental dynamics in a crystallization temperature range near Tg.
Isothermally crystallized copolymers display two melting peaks. The intensity of the low melting or aging peak increases with increasing aging time and crystallization temperature. Aging at temperatures above and below the maximum of the crystallization rates yielded a changeover in the contribution to the total heat of fusion of the low melting peak from 4.3% (smallest contribution) to 93% (largest contribution). The two melting peaks are attributed to two populations of crystals formed by a mechanism of sequence selection during isothermal crystallization.
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