We report the synthesis of polymethylene waxes, a surrogate of PE waxes, by a controlled polymerization reaction in water at or near r.t. and under atmospheric pressure. The monomer, dimethylsulfoxonium methylide, is generated in situ from a salt, trimethylsulfoxonium halide. The carbon sources for the polymerizations are C1 molecules, which can be derived from nonpetroleum feedstock. DMSO serves as the C1 carrier and is not consumed. The reaction is initiated and catalyzed by trialkylboranes, compounds that are stable in water. A certain degree of molecular weight control is achieved by adjusting the stoichiometry of "salt" to organoborane. Polymethylene, the simplest hydrocarbon polymer, is a semicrystalline material. The room temperature polymerization produces a linear polymer approximately 100 °C below its melting temperature (Tm). The supercooled polymers rapidly crystallize into flat nanoparticles comprised of stacked lamellae.