Controlling polymerization-induced phase separation in the synthesis of porous gels

Porous gels -- gels with solvent-filled pores that are much larger than their mesh size -- are widely used in engineering and biomedical applications due to their tunable mechanics, high water content, and selective permeability. Among various strategies to create porous gels, polymerization-induced phase separation (PIPS) has shown particular promise. However, the conditions that trigger and control PIPS remain poorly understood. Here, we systematically investigate the influence of solvent quality, polymeric precursor molecular weight, and polymer concentration on phase separation in polymerizing poly(ethylene glycol) diacrylate gels. We find that phase separation occurs when the precursor solution concentration is below the overlap concentration. Phase-separated gels have a pore geometry that is controlled by solvent quality: better solvents result in smaller pores, while worse solvents can create superporous, highly-absorbant gels. Motivated by our results, we propose a theory that predicts when phase separation occurs in polymerizing gels, applicable across a wide range of polymer/solvent gel systems. Our results provide a framework for the rational design of porous gels.