The second carbon atom remains available to grow the polymer chain . The attack of the double bond follows chemical rules, and there are situations in which the most nucleophilic atom is not available as a reactive site. As shown in Fig. , the structures of Poly(2-tbutyl-1,4-butadiene) and Poly(2-bromo-1,4-butadiene) contain t-butyl and bromine groups, respectively. These groups act as electron donors, increasing the electron population of the vicinal carbon atoms. However, because of their voluminous nature, they might also increase the steric hindrance in the region. The current version of the HTA algorithm does not incorporate specific rules for predicting steric hindrance. As a result, the head and tail positions were simply assigned to the region with the highest nucleophilicity.