Molecularly Imprinted Polymers and Room Temperature Ionic Liquids: Impact of Template on Polymer Morphology

Abstract

Molecularly imprinted polymers (MIPs) were generated for trans-aconitic acid 1 and cocaine 2 in a variety of porogens (CH₃CN, CHCl₃, [bmim][BF₄], and [bmim][PF₆]). MIP synthesis in either [bmim][BF₄] or [bmim][PF₆] resulted in significant acceleration of polymerization rates and, in the case of low temperature polymerizations, reactions were complete in less than 2 h, while no product was observed in the corresponding volatile organic carbon (VOC) porogen. In all instances, MIPs generated in [bmim][BF₄] or [bmim][PF₆] returned imprinting selectivities (I values) on par with or better than the corresponding MIP generated in VOCs. Imprinting values ranged between I = 1 and 2.9, with rebinding limited to 1 h. MIP synthesis conducted at low temperature (5°C) afforded the highest I values.

Scanning electron microscopy examination of MIP morphology highlighted an unexpected template effect with MIP structure varying between discrete nanoparticles and robust monoliths. This template–monomer interaction was also observed in the rates of polymerizations with differences noted in reaction times for 1 and 2 MIPs, thus providing indirect conformation of our previously proposed use of molecular modelling–nuclear magnetic resonance titrations (the MM-NMR method) in the design phase of MIP generation. In addition, considerable batch-to-batch rebinding selectivities were observed.