For a C-HC−H bond there is only marginal charge separation between the bound atoms; for a C-CC−C there should be no charge separation, as the bound atoms have no difference in electronegativity. For ethylene, H_2C=CH_2H2C=CH2, even if there were bond polarity, the molecular dipole would be zero because of the symmetry. Maybe styrene, C_6H_5CH=CH_2C6H5CH=CH2 should be a little more polar, however, the difference should be marginal.
Anyway, a styrene monomer is not going to stick around too long before it polymerizes.
