Methanimine is a molecule of interest in astrobiology, as it is considered an abiotic precursor of the simplest amino acid glycine. Methanimine has been observed in the interstellar medium and in the upper atmosphere of Titan. In particular, it has been speculated that its polymerization can contribute to the formation of the haze aerosols that surround the massive moon of Saturn. Unfortunately, such a suggestion has not been proved by laboratory experiments. Methanimine is difficult to investigate in laboratory experiments because it is a transient species that must be produced in situ. To assess its potential role in the formation of Titan's aerosol, we have performed a theoretical investigation of possible formation routes and dimerization. The aim of this study is to understand whether formation and dimerization of methanimine and, eventually, its polymerization, are possible under the conditions of the atmosphere of Titan. Results of high-level electronic structure calculations are reported.