Diethyl ether is considered to be a polar molecule that has partial negative and partial positive charges. The two different charges do not cancel each other out, but provide the molecule with distinct charges at different sections. As a result, it cannot dissolve ionic or non-polar molecules.
Polar molecules do not dissolve ionic molecules because ionic molecules have a distinct positive or negative charge. The presence of multiple charges in the polar molecule dissuades the ionic molecule from dissolving.
Nonpolar molecules do not dissolve in polar molecules because they do not contain any type of charge.
Polar molecules are only able to dissolve other polar molecules that also have a positive and negative charge.