Polymerization kinetics of pseudocrown ether network formation for facilitated transport membranes

摘要

Pseudocrown ethers were synthesized from the photopolymerization of metal complexes of poly(ethylene glycol 200) diacrylates (PEG200DA) to yield polymeric networks that can be used in facilitated transport membranes. Metal ions that potentially could be used as molecular templates were screened by first characterizing the polymerization of hydroxyethyl methacrylate (HEMA) in the presence of the metal salts. Thermal polymerizations and photopolymerizations were used to elucidate which metals adversely effect the polymerization reaction via radical scavenging, chain transfer, light absorption, and other side reactions. HEMA polymerizations were used to investigate these effects because only linear polymers can form, and there will be no rate effects from cyclization. Photopolymerizations of templated PEG200DA exhibited a decrease in autoacceleration as an indication of pseudocrown ether formation due to the reduction in the degree of cross-linking with cyclization. Four metal salts, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, and Cd(NO3)2·4H2O, were found to make suitable templating ions. Although Cu(NO3)2·(2.5)H2O and CrCl3·6H2O formed appropriate complexes with PEG200DA, these metals act as radical scavengers and did not permit the desired polymerization. The peak rate was decreased up to 69% for the partially dried Co(II)/PEG200DA complex at a metal concentration of 1.27 M. Facilitated transport membranes exhibited a selectively of 1.3 for potassium over sodium and 27.5 for potassium over neodymium, and a benchmark comparison was made to an analogous polymer inclusion membrane that contained dibenzo-18-crown-6 as the carrier which had similar selectivities.