Explain the role of Van der Waals forces in pvc plastic?

1 Answer
Aug 28, 2014

The main van der Waals forces in PVC are dipole-induced dipole forces.

van der Waals forces include dipole-dipole, dipole-induced dipole, and London dispersion forces. The most important forces in PVC are dipole-induced dipole attractions.

PVC is a polymer of vinyl chloride.

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It is tempting to say that the molecules line up as in the diagram below. It looks as if are dipole-dipole forces between adjacent molecules

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But the Cl atoms are large, and they stick out from the chain in random directions.

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It is difficult for the chains to lie close together. Where the chains do come close, there are van der Waals attractions.

The C-Cl bond is polar, with a partial negative charge on the Cl atom.

The Cl atom is most likely to come close to an H atom in a nearby molecule.

The C-H bond in the adjacent molecule is nonpolar, so the H atom has no charge.

When the Cl atom approaches, the partial negative charge on the Cl repels the electron cloud on the H atom. This causes a partial positive charge on the H atom and induces a C-H dipole.

Each dipole-induced dipole interaction is not strong. But there are so many of them that pure PVC is a hard, brittle solid.

The PVC in ropes is flexible because it contains a plasticizer to soften it.