Porous polyurethanes synthesized within high internal phase emulsions

Abstract

PolyHIPE are highly porous, emulsion‐templated polymers typically synthesized via free‐radical polymerization within a water‐in‐oil (W/O) high internal phase emulsion (HIPE) whose dispersed, aqueous phase occupies more than 74% of the volume. The synthesis of a polyHIPE containing biodegradable polymers is not straightforward because the presence of both an organic phase and an aqueous phase within the HIPE limits the type of polymerization reactions that can be used. This article describes the synthesis of polyHIPE containing biodegradable poly(ε‐caprolactone) (PCL) groups through the step‐growth reaction of a diisocyanate with a flexible PCL triol to form a crosslinked polyurethane. The reaction of the diisocyanate with the water in the HIPE produced urea groups and large bubbles from the generation of CO2. The polymer walls between these bubbles consisted of a porous, emulsion‐templated structure. Polymerization with an excess of diisocyanate produced a significant enhancement in the amounts of urea and CO2. The reduction in the flexible PCL content and the enhancement in the rigid urea content produced an increase in wall modulus that was over 20‐fold. The ability to synthesize polyHIPE through such step‐growth reactions is an important advance in the adaptation of polyHIPE for such applications as tissue engineering. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5806–5814, 2009

Low density biodegradable shape memory polyurethane foams for embolic biomedical applications

“…[14] Related compositions of PCL-t (900 g) with HDI have been reported by David et al using the HIPE process; however, the foams were relatively dense with a non-uniform cell structure. [30] The use of the gas blowing process for these compositions, as reported here, not only enabled reasonably low densities (0.020-0.093 g cm -3 ), but also gave a very uniform cell morphology. In part, this is a result of optimization of the DCI990 and DC5179 surfactants to better stabilize the foam structure in the presence of the relatively high molecular weight PCL-t (900 g).…”

“…It is noteworthy that a single glass transition was seen for all materials. Absence of any secondary transition indicates an amorphous network structure, and formation of an all-encompassing crosslinked network with no isolated pockets of unreacted monomer that were reported for related compositions by David et al[30]…”

“…For instance, fabrication of related polyurethane foams from PCL-t and HDI using the High Internal Phase Emulsion (HIPE) templating process by David et al produced comparatively higher densities (0.21 g cm -3 ), with large variation in pore size ranging from ∼1 mm (from the CO 2 bubbles during reaction of isocyanate with water) to ∼ 0.1-100 um. [30]…”

Injectable PolyHIPEs as High-Porosity Bone Grafts

“…Biodegradability was achieved by substituting in unsaturated polyesters; however, the macromers studied were often too viscous to form HIPEs without the use of a toxic diluent, such as toluene. 27, 36, 40–41 …”

Achieving Interconnected Pore Architecture in Injectable PolyHIPEs for Bone Tissue Engineering

“…10,20,27 Subsequently, fully biodegradable systems were achieved by eliminating styrene and utilizing polyurethane and fumarate chemistries. 28,29 Although these compositions were biodegradable, the necessity of a toxic diluent and cure temperatures at or above 60°C rendered them noninjectable. An injectable polyHIPE system requires low viscosity macromers for HIPE formation without the need for a toxic diluent and reaction kinetics permitting cross-linking in situ.…”