Two Structurally Different Polymers from a Single Monomer

We designed and synthesized a malonamide-derived monomer, containing azide and alkyne units, for topochemical polymerization to yield nylon (n,3). This monomer on crystallization gave two concomitant polymorphs <b>M1</b> and <b>M2</b>. Both the polymorphs show crystal packings that are suitable for topochemical azide–alkyne cycloaddition polymerization. On heating, polymorph <b>M1</b> reacts regiospecifically to give 1,4-disubstituted-1,2,3-triazolyl-linked polymer, whereas polymorph <b>M2</b> yields 1,5-disubstituted-1,2,3-triazolyl-linked polymer regiospecifically. In the case of polymorph <b>M1</b>, polymerization proceeds perpendicular to the hydrogen bonding direction, whereas in <b>M2</b>, the reaction occurs along the hydrogen bonding direction. This results in the two structurally different polymers having distinct topologies. These single-crystal-to-single-crystal polymerizations allowed us to study their structure at atomic resolution by single-crystal X-ray diffraction. This is the first report on the topochemical synthesis of two structurally isomeric polymers from a single monomer.