Facile fabrication of doubly porous polymeric materials with controlled nano- and macro-porosity

Abstract

A critical overview of the different parameters affecting the porous features of doubly porous polymeric materials based on poly(2-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate) (poly(HEMA-co-EGDMA)) and designed via a double porogen templating approach is presented. A thorough investigation was accomplished so as to highlight the main advantages of the proposed double porogen approach which relied on the distinct and independent control of both porosity levels, i.e. nano- and macro-porosity. The nanoporosity level was produced via a phase separation phenomenon that occurred during the polymerization of the comonomers in the presence of various porogenic solvents. To generate the macroporosity, three straightforward and versatile strategies were implemented through the use of sodium chloride (NaCl) macro-sized particles. The first one implied the use of non-sintered NaCl particles that allowed for the creation of non-interconnected macropores. The other two strategies involved the sintering of NaCl particles prior to the generation of the poly(HEMA-co-EGDMA) network. In the latter case, NaCl particles were fused through two different methods, either through sintering at 730 °C or by Spark Plasma Sintering. Upon porogen removal, doubly porous PHEMA-based materials were obtained with macropores having NaCl particle imprints in the 100 μm order of magnitude, while the second porosity level laid within the 10 nm to 10 μm order of magnitude, as evidenced by mercury intrusion porosimetry and scanning electron microscopy, depending on the solvent structure, its volume proportion, and the cross-linker concentration in the polymerization feed. A full porous characterization was carried out in order to clearly understand the effect of such structural parameters on the porosity of the as-obtained doubly porous polymeric materials and their nanoporous counterparts.