Under pressure: Temperature‐dependent optical transmission in aqueous solution is exhibited by polyurethanes that are obtained by copolymerization of 2‐methylaziridine and supercritical CO2 (scCO2; see scheme). The transmittance drops sharply at the lower critical solution temperature (LCST). The molecular weight, content of urethane linkages, and LCST value of the polyurethanes are controllable simply by changing the CO2 pressure.

A reaction of aziridines and carbon dioxide (CO2) proceeds under supercritical conditions to give random copolymers containing urethane and amine moieties. The ratio of urethane and amine linkages in the product can be controlled by reaction conditions including temperature and pressure as well as addition of N,N-dimethylacetamide as a cosolvent. An aqueous solution of the copolymer obtained from 2-methylaziridine and CO2 undergoes a thermally induced phase transition at a lower critical solution temperature (LCST). The critical temperature is highly sensitive to changes in the primary structure of the products. The use of supercritical CO2 (scCO2) allows us to construct a functional material through the effective chemical fixation of CO2.

Copolymeric products from 2-methylaziridine and carbon dioxide showed sharp and rapid phase transitions in response to both temperature and pH; the responsive property can be controlled by varying the reaction conditions whilst maintaining the supercritical state.

Supramolecular liquid-crystalline polymeric complexes derived from polyamides containing 2,6-bis(amino)pyridyl units in their main chains and benzoic acid derivatives have been obtained by the formation of intermolecular double hydrogen bonds. The polymeric complexes behave as single liquid-crystalline polymers and exhibit stable and enantiotropic mesophases. The hydrogen-bonded mesogens laterally connected by flexible spacers form a polymeric structure that is not simply classified as a main-chain or a side-chain type.