Question

In which polymer, polyethylene or polyvinyl chloride, would you expect to find the stronger intermolecular forces, assuming that the average chain lengths are equal?

Short answer

Polyvinyl chloride has stronger intermolecular forces because dipole-dipole forces are stronger than London dispersion forces.

Step-by-step solution

To find the polymer

Only difference between these polymers is in one chlorine atom. Bond (C-Cl) is polar because of the difference in each atom's electronegativity.

Polyethylene does not have polar bonds and the only intermolecular force that occurs between two polyethylene chains is the London dispersion force.

The Polyvinyl chloride unit is polar and therefore dipole-dipole interactions occur between two polyvinyl chloride chains.

Since dipole-dipole interactions are stronger than London dispersion forces, polyvinyl chloride will have stronger intermolecular interactions.

Hence Polyvinyl chloride has stronger intermolecular forces because dipole-dipole forces are stronger than London dispersion forces.