Emulsion templating of simultaneously-synthesized interpenetrating polymers with degradable components for hierarchical porosities

Abstract

Hierarchically porous polymers are of interest for a variety applications including adsorption, catalysis, scaffolds, energy storage, and controlled release. In this work, two simultaneous, mutually exclusive reactions within the external phases of water-in-oil high internal phase emulsions (HIPEs) were used to generate macroporous semi-interpenetrating polymer network (semi-IPN) polyHIPE monoliths. The styrenic copolymer of vinylbenzyl chloride (VBC) and divinylbenzene (DVB) was synthesized using free radical polymerization. The non-crosslinked poly(urethane urea) (PUU), based on a polycaprolactone (PCL) triol, was synthesized using step-growth polymerization. The open-cell, semi-IPN polyHIPEs had densities of ∼0.17 g/cm3, corresponding to porosities of ∼84 %. The semi-IPN polyHIPE with the higher P(VBC-co-DVB) content (75 wt %) exhibited a porous structure typical of polyHIPEs, with an average void diameter of ∼10 μm. The porous structure of the semi-IPN polyHIPE with the lower P(VBC-co-DVB) content (50 wt %) resembled a network of channels. Hierarchical porosities were generated by either etching the flexible PCL-based non-crosslinked PUU to generate mesoporosity or by hypercrosslinking the stiff styrenic copolymer framework to generate microporosity. Etching the semi-IPN polyHIPEs in 3 M NaOH removed most of the PUU. Hypercrosslinking generated microporosity and specific surface areas of 445 and 176 m2/g for 75 and 50 wt % P(VBC-co-DVB), respectively. In the semi-IPNs, the hypercrosslinking process also generated mesoporosity from the removal of some of the PUU.