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Modern Polymer Spect..

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138 3 Vibrcitional <strong>Spect</strong>ru as a Probe oj Stnrcttiral Order<br />

dl<br />

w=3a1 a cm-‘<br />

el<br />

w=355.0 cm-’<br />

Figure 3-23. Examples of resonance<br />

modes in the bending region for a<br />

single chain of mixed 25% DCI in<br />

HCl.<br />

3.12 CIS-trans Opening of the Double Bond in the<br />

<strong>Polymer</strong>ysation of Ethylene<br />

The method just outlined was used, at the earlier stages of these kinds of study<br />

[loll, for the elucidation of the mechanism of polymerization which was, at that<br />

time, an unsolved puzzle. The chemical problem can be stated briefly in the following<br />

way: when ethylene is polymerized using Ziegler-Natta catalysts a linear<br />

polymer is formed. It was known that the catalysts acts on the double bond of the<br />

ethylene unit and the polymethylene chain can grow on both sides of the ethylene<br />

unit once the double bond has been opened. The opening, however, can occur in cis<br />

or trms configuration.<br />

H H H I H<br />

‘c-c’<br />

‘c-c’<br />

H/I J\H H’ l\H

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