Ft-Ir Study of the Dynamics of Entangled Polymer Melts
Lee, Andre Yan-Jyh
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https://hdl.handle.net/2142/71842
Description
Title
Ft-Ir Study of the Dynamics of Entangled Polymer Melts
Author(s)
Lee, Andre Yan-Jyh
Issue Date
1987
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Abstract
The dynamics of entangled polymer melts have been examined using polarized Fourier-Transform infrared (FT-IR) spectroscopy. Based on the reptation model, the motion of a chain in the presence of topological entanglements is that of a one dimensional random walk along the chain contour. This motion allows the end portions of the chain to escape the initial oriented tube and form a new tube. The new tube is assumed to have a random orientation. Therefore, we utilized the infrared dichroism technique to quantitatively measure the orientation relaxation of the uniaxially strained polymer melts, which gives a direct measure of the fraction of the chain which remains in its initial tube. Three types of experiments were done to study the dynamics of linear entangled polymer melts. (1) Homo-polymer Melts. In this case, different monodisperse molecular weight atactic polystyrenes were used, and the FTIR measured the normalized Hermans orientation function, F(t), as a function of relaxation time, t, and molecular weight, M. We observed that F(t) = 1 $-$ $\alpha$t$\sp{1/2}$M$\sp{-3/2}$, for t $$ P, and became independent of P when M $$ P, the matrix chain can move faster than the labelled chain. Thus, some segments of the labelled chain are relaxed due to the constraint release of the surrounding matrix chains. (3) Relaxation Mechanism. A centrally deuterated triblock polystyrene was used. The FTIR results showed that the deuterated center block loses little orientation initially and then decays in a predictable exponential manner after some time. These observations strongly support the reptation model for melt dynamics. In this thesis, we have showed that infrared dichroism is an excellent method to study the polymer melt dynamics, and the reptation model provides a good description for the motion of entangled polymer chains.
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