Microporous, responsive hydroxypropyl cellulose gels. 1. Synthesis and microstructure

An effective technique for the synthesis of microporous gels is developed along with correlations between synthesis conditions and microstructure. Such gels have substantially different properties than their nonporous analogues. Microporous hydroxypropyl cellulose (HPC) gels were prepared by heating aqueous HPC solutions above their lower critical solution temperatures (LCST's) while cross-linking the polymer with divinyl sulfone. The effective porosity of the gel increased from 23 to 76% by decreasing HPC concentration from 22.6 to 9 wt%, as anticipated from the system phase diagram. The pore size range decreased from 0.5-9.0 to 0.05-0.2 mu m by increasing reaction time before phase separation from 1.5 to 25 min, demonstrating that cross-linking in the homogeneous state limits the extent of phase separation possible. Gel morphology changed from open-celled to closed-celled by decreasing reaction time in the phase-separated state, which limits cross-linking in the polymer-rich phase.