Synthesis, Characterization, and Structure of Glassy Diacetylene-Containing Segmented Block Copolyurethanes

Diacetylene-containing segmented block copolyurethanes were prepared from 4,4′-diisocyanodiphenylmethane, 2,4-hexadiyne-1,6-diol, and a poly(propylene glycol) using a one-shot bulk polymerization process. Two copolymer series were produced: one containing different diacetylene contents and the second containing different amounts of a second short-chain diol, dipropylene glycol, but with approximately constant diacetylene content. The as-prepared, linear copolymer precursors were then thermally cross-polymerized via solid-state topochemical reactions within the diacetylene-containing phase, to yield insoluble and infusible materials. All the cross-polymerized copolymers were rigid at room temperature with glass transition temperatures ranging from 40 to 100 °C (DMTA). The effects of copolymer composition and the conditions for cross-polymerization on the morphology and properties of the materials were extensively studied using thermal and spectroscopic techniques. Transmission electron microscopy showed clearly the diacetylene-containing spherulites to be uniformly dispersed in the continuous, amorphous poly(ether‒urethane) matrices. Significant phase mixing and disruption of the solid-state topochemical reactions in the copolymers resulted when the additional glycol DPG was introduced. Resonance Raman spectroscopy proved extremely useful for following the in situ formation of the polydiacetylene chains within the dispersed phase and for providing information concerning copolymer morphology.