If the dipoles are not too large, and the temperature is not too low, the dipoles modify (and tend to strengthen) the attractive branch of the Lennard-Jones function.
Often it is convenient to consider the dipole moments associated with small collections of atoms, such as a nitrile (two atoms, C and N), ether (three atoms, C-O-C), or amide (four atoms, CONH). Then partial charges can be distributed over these atoms, and the interactions between two dipoles can be calculated using these partial charges and Coulomb's Law.
E = zi zj/(4 pi epsilon0rij)
Partial charges may produce important interactions even in systems that do not have a permanent dipole moment. Consider benzene as an example. The hydrogen atoms bear a partial positive charge, and the carbon atoms bear a partial negative charge of the same absolute value. Symmetry considerations show that the centers of positive and negative charges are coincident, and no permanent dipole moment exists. The system has a quadrupole moment instead. This quadrupole moment, evaluated using Coulomb's law and the partial charges, has an important influence on the "structure" in liquid benzene, and on the preferred modes of packing of the aromatic rings in amorphous polystyrene. Therefore polar interactions in polymers are not limited to dipole moments.
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