We describe the results of the topochemical polymerization of p-xylylenediammonium disorbate as the bifunctional monomer in the crystalline state via a radical chain polymerization mechanism. The structure and properties of the resulting double-stranded polymer are investigated by X-ray crystal structure and thermal analyses as well as IR spectroscopy. The stereochemical structure of the polymer is confirmed by NMR spectroscopy after the solid-state transformation of the polymer side chain to give the single-stranded chains that are soluble in methanol. We propose a model for the reaction mechanism to provide a ladder polymer in the crystalline state on the basis of the results of single-crystal structure analysis and the observation of the alpha -methyl and alpha -carboxylate propagating radicals by ESR spectroscopy. The two reaction parts of the monomer are synchronized to simultaneously react with the conformational change in a sorbate moiety that is transformed into another sorbate through the diammonium part as the linker.