Spontaneous Single-Crystal-to-Single-Crystal Evolution of Two Cross-Laminated Polymers

Two cases of spontaneous evolution of monomers to linear polymers having novel cross-laminated topology are reported. We synthesized two peptide monomers N-3-Gly-Gly-NH-CH2-CCH and N-3-Gly-Gly-Gly-CH2-CCH and solved their crystal structures by single-crystal X-ray diffraction. They adopt H-bonded crisscrossed layered packing in their crystals such that: (a) the monomers are aligned head-to-tail in 1D-chain-like arrays and parallel arrangement of such arrays forms a layer; (b) the proximally placed azide and alkyne motifs are in an orientation apt for their regiospecific cycloaddition; (c) each monomer having x peptide bonds is H-bonded with 2x monomers disposed in intersecting arrangement, which pre-organize 1D-chain-like arrays in adjacent layers in perpendicular orientation. These crystals underwent spontaneous single-crystal-to-single-crystal (SCSC) polymerization via azide-alkyne cycloaddition reaction to form triazolyl-polyglycines, at room temperature. The crisscrossed arrangement of monomers in adjacent layers ensured the formation of cross-laminated polymers.