Does polychloroethylene have only van der Waals/London forces between its molecules? Surely, if all the chlorine atoms are on one side, due to the fact that chlorine is more electronegative than carbon, shouldn’t it have permanent dipole-dipole forces?
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2$\begingroup$ Everything has London forces. $\endgroup$ – Ivan Neretin May 24 '18 at 17:12
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$\begingroup$ There are permanent dipoles there,so no idea why you'd think otherwise. $\endgroup$ – Mithoron May 24 '18 at 17:24
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$\begingroup$ PVC tends to have a relatively high stereoregularity, for sth. made by radical polymerisation, but a local dipole moment perpendicular to the backbone would be there any way. Not a very large one, compare methylene chloride, chloroform, etc. $\endgroup$ – Karl May 24 '18 at 18:29
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$\begingroup$ @Karl dipole moment can be completely cancel out by C-C rotations...it follows of your reasoning... $\endgroup$ – user43021 Sep 23 '18 at 2:07
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$\begingroup$ @santimirandarp hm, C-C rotations are not so easy in a polymer backbone, especially if it's substituted with a bulky chlorine atom $\endgroup$ – Karl Sep 23 '18 at 10:02
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No, but for polymers of any reasonable size, the dispersion (and excluded volume) forces completely overwhelm any dipole-dipole forces, since they grow with the size of the molecule and dipole-dipole forces do not. Also, bear in mind that the chlorines aren't all on one side of the molecule first because the way it's manufactured tends to put Cls randomly on each side of the chain, and second because the molecule has considerable conformational flexibility. That's true even in the solid state, which for polymers is usually substantially glassy with interspersed domains of crystal.
answered May 25 '18 at 2:38
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$\begingroup$ PVC has a rather high stereoregularity, not random atactic, and ist partially crystalline, ordinary polystyrene is just an amorphous glas, PE is partially crystalline and it's glass transition temperature is below -60°C. ?!? $\endgroup$ – Karl May 27 '18 at 16:19
