A ionic molecular binding connects atoms A characterized by a number of free positions in their valence shell with atoms B which have the number of valence electrons exactly fitting to the spare positions of atom A. For connecting both atoms the superfluous electrons of atom B migrate to the spare positions af A. So A and B are no more charged neutral but A is charges neagtive and B is charged negative. So the new molecule A=B has a negative electric pole at A and a positive electric pole at B. His results in electric polarity and in an electric dipole moment.
Even molecules with dipole bindings can be neutral if two or more bindungs within the molecule compensate themselves. An example for such a molecule which is completely symetric is Methan which is non polar despite its 4 C-F-bindings.
All polymers of Methan are non polar as well.