Molecular dynamics computer simulation of three substances ethylbenzene (EB), pentastyrene (PS-5), and polystyrene-25 (PS-25) was performed to investigate the local order of the phenyl rings in monomers and side-chain polymers. Monomer molecules (EB) tend to be in T-configuration, which corresponds to isotropic local structure. Phenyl rings in chained molecules PS-5 and PS-25 partly cooperate in both parallel-displaced and “sandwich” configuration with π–π stacking. These configurations are locally anisotropic and lead to the increasing of Kerr constant K. Analysis of the local structure was performed by calculating the cylindrical distribution function.