Porosity control in high internal phase emulsion templated polyelectrolytes via ionic crosslinking

A series of novel macroporous materials based on poly(N‐isopropylacrylamide)‐b‐sodium polyacrylate is synthesized via aqueous reversible addition‐fragmentation chain transfer polymerization in an oil‐in‐water high internal phase emulsion (HIPE) utilizing both covalent and ionic crosslinkers (PEG diacrylate and calcium diacrylate, respectively). Porosity is directly related to the calcium diacrylate content of the polyHIPE. Depth profiling XPS of pressed samples reveal the segregation of less polar substituents (PNIPAM, PEGDA) to the interface, whereas ionic components are located deeper within the continuous aqueous phase, primarily driven by ionic strength. This segregation of components stabilizes the internal‐continuous phase interface and results in decreased void diameter. Calcium diacrylate also forms ionic crosslinks in the polyHIPE material, resulting in increased interconnecting pore diameter due to volume contraction upon polymerization. Evidence of volume contraction is provided by the stress induced on PEG at the o/w interface by internally located calcium polyacrylate crosslinks, resulting in a decrease in XRD peak intensity. It is therefore proposed that calcium diacrylate is capable of modifying polyHIPE morphology via two separate mechanisms. Published 2016 1 . Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2486–2492