Solvent-induced self-organization approach for polymeric architectures of micropores, hexagons and spheres based on polyurethanes prepared via novel melt transurethane methodology

Solvent-induced self-organization approach was developed, for the first time, to produce polyurethane microporous templates and higher ordered morphologies such as micro or nanometer-sized polymeric hexagons and spheres. A novel melt transurethane methodology was designed and developed for synthesizing new class of cycloaliphatic polyurethanes under nonisocyanate and solvent-free conditions. In this new process, a diurethane monomer was polycondensed with equimolar amounts of diol in presence of Ti(OBU)(4) as catalyst with the removal of low boiling alcohol from the equilibrium. The hydrogen bonding of the polyurethanes are very unique to their chemical structure and they undergo selective phase-separation process in solution to produce hexagonally packed microporous templates. The increase of water content in the polymer solution enhances the phase-separation process and the micro pores coalesce to isolate the encapsulated polymer matrix into polymeric hexagons or densely packed solid spheres. The concentration-dependent solution FTIR and H-1 NMR of the polyurethanes revealed that the polymers possessing higher H-bonding association constants (K) have greater tendency to undergo solvent-induced self-organization phenomena. The mechanism of solvent-evaporation process indicated that only microporous polyurethanes have tendency to form higher ordered hexagons and spheres whereas others failed to show any new morphology. (C) 2007 Wiley Periodicals, Inc.