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Dielectric polymers such as polyethylene (PE) have a wide range of energy and electronic applications. While recent studies have shown significant effects of chemical defects on the electronic structure of PE, those on the dielectric properties remain elusive. Here, first-principles quantum-mechanical calculations show anisotropic dielectric constants of PE, which are sensitive to the type of defects. Specifically, addition of iodine defects increases the high-frequency dielectric constant. Addition of hydroxyl or carboxyl group, on the other hand, causes noticeable anisotropic changes in the static dielectric constant, which is well elucidated through the rotation and concerted motions of chemical groups. The sensitivity of these defects may be exploited to rationally alter the behavior of PE. [ABSTRACT FROM AUTHOR]