Functional polymers, a significant class of compounds with diverse applications, are synthesized by incorporating functional groups into polymer matrices. Poly(epichlorohydrin) (PECH) is a pivotal polymer due to its reactive chloromethyl group, which readily enables its transformation into various functional polymers. Our study is focused on theoretically unraveling the mechanism behind modifying PECH through menthol grafting. We optimized and characterized various stationary states using Density Functional Theory (DFT) at the B3LYP/6-311++G** level. These calculations were conducted in both gas phase and a solution environment (THF). To anticipate the specific sites within our polymer that would be subject to grafting, we calculated various reactivity indices at the same computational level.