Microporous polyurethanes: Synthesis and investigation of the mechanism of the pore formation

Abstract

A new approach for microporous polymeric material is developed utilizing the secondary interactions such as hydrogen bonding in the polymer chains in polyurethane systems at ambient conditions. A new series of highly rigid, thermally stable, and readily soluble cycloaliphatic polyurethanes were designed and synthesized for this purpose, based on new tricyclodecanedimethanol and 1,4-cyclohexanedimethanol. The hydrogen-bonding interactions induce phase separation in solution, which leads to polymer-rich and solvent-rich domains; subsequent evaporation of the solvent molecules results in micropores. The phase-separation process in the polyurethane is found to be highly dependent on the chemical structures of the polymer chain backbone. H-1 NMR titration experiments were carried out to understand the mechanism of the micropore formation and its dependence on different structural subunits. The hydrogen-bonding association constant (K) obtained from the titration experiments revealed that higher the K-value more the tendency to form micropores. A fully cycloaliphatic polyurethane produces micropores of sizes ranging from 1 to 8 pro, and each pore is separated by 10(-20) mu M, whereas the replacement of one of the cyclic unit in the backbone disturbs the entire phase-separation process and results in nonporous morphology.