A quantitative investigation of crystalline and amorphous components of trans-polybutadiene.
Item
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Title
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A quantitative investigation of crystalline and amorphous components of trans-polybutadiene.
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Identifier
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AAI8820909
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identifier
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8820909
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Creator
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Wang, Peiguo.
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Contributor
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Adviser: Arthur E. Woodword
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Date
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1988
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Polymer
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Abstract
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Polybutadiene lamellas containing 89% and 99% trans units were grown from solution and were investigated by the technique of surface epoxidation coupled with by C-13 NMR analysis. It was found that under proper suspension conditions all of and only monomer units in the surface (amorphous) part can be epoxidized. Since the resonances of the junction carbons between epoxidized and unepoxidized sequences can be separated from other resonances in the C-13 NMR spectrum, both the average crystalline stem length (A) and the average fold length (B) could be evaluated.;For the lamellas prepared from 99%-trans-polybutadiene, both A (17-24 monomer units) and B(5-9 monomer units) values increase with crystallization temperature, but they are not affected by the solution concentration. It was found that cis units and chain ends are rejected from the crystalline core, leading to some larger folds with additional trans units. Correcting for this rejection effect yields a minimum fold length of three to four monomer units.;A general statistical treatment has been established for the calculation of the crystallinity and a characteristic tetrad ratio as functions of the crystalline stem length (A), the minimum fold length (B{dollar}\sp\prime{dollar}), equivalent cis-units ({dollar}q\sb1{dollar}) and the degree of polymerization ({dollar}X\sb{lcub}n{rcub}{dollar}). Both calculated crystallinity and tetrad ratio fit the experimental data with a minimum fold length of three or four monomer units.;For lamellas prepared from 89%-trans-polybutadiene A-values do not change with crystallization temperature, solvent and solution concentration. The experimental piont (A of 11 and crystallinity of 0.41) falls on a theoretical curve with a minimum fold length of three. Since three monomer units is the minimum length for folding in trans-polybutadiene lamellas, the results obtained from both 89% and 99% trans-polybutadiene samples strongly favor tight adjacent reentry.;In amyl acetate a critical at 10{dollar}\sp\circ{dollar}C gelation concentration for 89%-trans-polybutadiene is found to be 0.7% (w/v). A fold entanglement mechanism for gelation was proposed.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
