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. 1H 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 μm, and each pore is separated by 10−20 μm, whereas the replacement of one of the cyclic unit in the backbone disturbs the entire phase‐separation process and results in nonporous morphology. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1296–1308, 2006

Polycarbonate polyurethane elastomers synthesized via a solvent‐free and nonisocyanate melt transesterification process

“…Deepa and coworkers have recently published articles about this method that have also focused on the synthesis process, using urethane and low‐boiling alcohols such as 1,4‐butanol as the reactants and titanate as the catalyst. The PU product is a kind of white powder with no soft segment in the structure.…”

Solvent‐free and nonisocyanate melt transurethane reaction for aliphatic polyurethanes and mechanistic aspects

“…Some of the polymers were partially soluble in THF (see Table 1), and therefore, the reported molecular weights for these polymers were corresponding to the THF‐soluble fraction of the sample. GPC molecular weights of the polymers indicate the formation of moderate to high‐molecular weight polymers, and the values also proved that the melt transurethane process was superior to the conventional isocyanate route for the synthesis of polyurethanes 33. The polymers prepared from the cycloaliphatic diols (TCD‐DM and CHDM) showed much higher molecular weights compared with that of oligoethylene glycols, which may be due to the difference in the hydrodynamic volume for the polymers in THF solvent.…”

“…GPC molecular weights of the polymers indicate the formation of moderate to highmolecular weight polymers, and the values also proved that the melt transurethane process was superior to the conventional isocyanate route for the synthesis of polyurethanes. 33 The polymers prepared from the cycloaliphatic diols (TCD-DM and CHDM) showed much higher molecular weights compared with that of oligoethylene glycols, which may be due to the difference in the hydrodynamic volume for the polymers in THF solvent. The molecular weight data gave clear evidence that the nature (primary and secondary) of the carbamate monomer did not make much difference, as compared with that of the nature of the diols in the formation of higher molecular weight chains.…”

“…A urethane linkage can be considered as a half‐ester‐half‐amide bond (ROCONHR′), and during the transurethane process the ester bond in the diurethane monomer (or carbamate) cleaved selectively so as to form the new urethane linkage. Recently, a series of fully cycloaliphatic polyurethanes prepared based on the new process were allowed to undergo solvent‐induced self‐organization for polyurethane nanostructured morphologies such as pores, hexagons, and spheres 33, 34…”

“…Recently, a series of fully cycloaliphatic polyurethanes prepared based on the new process were allowed to undergo solvent-induced self-organization for polyurethane nanostructured morphologies such as pores, hexagons, and spheres. 33,34 This investigation is emphasized on development of melt transurethane process for polyurethanes, and investigate the mechanistic aspects of the process in detail for sustainable and efficient alternative methodologies for polyurethanes under solvent-free and nonisocyanate conditions. The diurethane (also mono) monomers were easily synthesized by condensing a diamine (or monoamine) with dimethyl carbonate (DMC) in presence of a base in good yield and high purity.…”