Polymers
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For polymers, as the temperature increases from very cold to hot, the plastic goes from being a brittle solid to a liquid. The glass transition temperature is when the polymer becomes flexible. I realise this can be explained by knowing that at lower temperatures molecules can't slide over each other as easily, but does the proportion/ratio of amorphous:crystalline regions alter with temperature? What is happening to the intermolecular forces at the melting point/glass transition temperature?
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Ulex replies
Unfortunately I am not an expert on polymer properties. However, I do know that the glass temperature depends on a number of things. One of these is the rate of cooling/heating. Slow cooling from the liquid state results in a higher glass temperature than rapid cooling because the molecules have time to orient themselves into crystalline confirmation.
For this reason, I would think that the proportion of amorphous to crystalline regions does alter with temperature. As you will appreciate, it is not so much the intermolecular forces which change during heating/cooling, it is the kinetic energy of the molecules which changes, altering the extent to which the intermolecular forces can be overcome.
The whole business is quite complex. You might be interested in some teaching material from the University of Cambridge; the url is:
www.doitpoms.ac.uk/tlplib/glass-transition/theory1.php
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updated: 14 April 2008
