Synthesis of degradable polyHIPEs by AGET ATRP

Conditions to synthesize a degradable polymerized high internal phase emulsion (PolyHIPE) by a controlled radical polymerization (CRP) method, atom transfer radical polymerization (ATRP), have been developed for the first time. Activators generated by electron transfer (AGET) ATRP were used to copolymerize 2-ethylhexyl methacrylate (EHMA) and bis(2-methacryloyloxyethyl) disulfide (DSDMA), a degradable cross-linker, in a HIPE system without the removal of oxygen. These conditions provided control over the polymerization and resulted in a fully degradable material. The degradation product had molecular weight M_n = 30,500, and relatively low dispersity, M_w/M _n = 1.6, indicating that a uniform cross-linked network was formed. Superior control over the polymerization resulted from the selection of a highly hydrophobic ATRP catalyst, CuBr₂ with an N,N-bis(2-pyridylmethyl) octadecylamine (BPMODA) ligand, which is preferentially located in the organic phase. Alternate conditions with a less hydrophobic catalyst, CuBr₂ with a 2,2′-bipyridine (bpy) ligand, result in a non-degradable polyHIPE. The CuBr₂/bpy catalyst predominately partitions into the aqueous phase where it exerts little control over the polymerization. The polyHIPE synthesized using a CuBr₂/BPMODA catalyst also exhibited a higher Young's modulus and was stiffer, due to its more uniform cross-linked network, than materials from almost identical HIPEs synthesized using a CuBr ₂/bpy catalyst.