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 CuBr2/bpy catalyst. (c) 2013 Elsevier Ltd. All rights reserved.