Functionalized Mesoporous Polymers with Enhanced Performance as Reference Electrode Frits

Mesoporous glasses (∼10 nm pores) and macroporous polymers (∼1 μm pores) are often used as frits in the fabrication of aqueous reference electrodes. These frits function as salt bridges that allow for electrical contact between the sample and reference solutions while slowing cross contamination of the two solutions. Unfortunately, mesoporous glass and macroporous polymer frits used for these purposes inherently result in sample-dependent potentials or in rapid cross contamination of the sample and reference solutions, respectively. To address these issues, we synthesized mesoporous polymer frits, with much smaller pore sizes (∼10 nm) and electrically neutral hydrophilic pore walls. These monoliths were prepared from a bicontinuous, microphase-separated, and cross-linked block polymer precursor, that is, poly(lactide)-b-poly(isoprene)-b-poly(styrene-co-divinylbenzene), PLA-b-PI-b-P(S-co-DVB). The PLA serves as a selectively etchable sacrificial block, the PI provides latent reactive sites on the pore walls, and the P(S-co-DVB) forms the mechanically robust matrix. Subjecting the PI repeat units in the monoliths to epoxidation and subsequent hydrolysis reactions renders the pore walls hydrophilic and uncharged, permitting the use of the polymer as a porous frit material in reference electrodes with aqueous electrolyte solutions. This monolith chemistry allows for reference electrodes with reduced flow rates that approach those of mesoporous glass frits and thus mitigated cross contamination. Moreover, reference electrode potential variations are reduced across a large range of electrolyte concentrations.