Synthesis and Ion-Binding Properties of Polymeric Pseudocrown Ethers - a Molecular-Dynamics Study

A novel method for producing inexpensive polymeric pseudocrown ethers in situ during free-radical polymerizations was investigated using molecular dynamics simulations. This scheme is based upon a template ion and exploits the tendency of oligomeric ethylene glycol diacrylates to form intramolecular cycles during polymerization. In the scheme, a template ion is used to induce the poly(ethylene glycol) diacrylates (PEGDA) to assume cyclic structures before polymerization with a comonomer. Experimental studies demonstrated that certain salts that were insoluble in nonpolar solvents were solubilized upon the addition of oligomeric poly(ethylene glycol) (PEG) due to complexation. Further evidence of cation binding by oligomeric PEG was obtained by H-1 NMR studies of PEG and its complexes with metal salts. To optimize the template ion synthesis approach, molecular dynamics simulations were performed on PEGDA containing between two and ten ethylene glycol repeating units, with and without the presence of cations. Simulation results indicated that the presence of the templating cation significantly decreased the mean end-to-end distance, thereby bringing the unsaturated endgroups into close proximity. The PEGDA ligand that resulted in the most effective templatization for Na+ contained four ethylene glycol repeating units. Simulation times greater than 50 ps had little effect on the results for ligands containing 7 or fewer ethylene glycol repeating units.