Generally, yes polar molecules are more reactive. For example, benzene is unable to polarise bromine so they can't react, whereas phenol can; bromine is polarised and is therefore able to react. Halogens are very electronegative: Fluorine is the most at 4.0. H-Cl, eg, is held by a polar covalent bond.
Similarly, iodoalkanes have polar covalent bonds:
Iodine: 2.66; Hydrogen: 2.1. The elctronegativity difference = 0.56, and any value between 0 and 1.8 is polar covalent. (if 0 = covalent - non polar, and if >1.8 = ionic)
Iodoalkanes are more reactive than alkanes because they do have polar covalent bonds.
... and the ones that won't