Characterisation and improved performance of molecularly imprinted polymers prepared using room temperature ionic liquids

Molecularly Imprinted Polymers (MIPs) are selective recognitions elements that have biological, chromatographic and sensory applications. While methods exist to reproducibly form MIPs with high affinity for a wide range of target molecules, improvements in production efficiency and selectivity are constantly being sought. Room Temperature Ionic Liquids (RTILs) represent a reasonably novel class of ‘green solvents’ which have been widely utilised for polymerisation reactions, resulting in enhanced polymerisation rates and polymer yields. In this study, the performance of imprinted polymers prepared in RTILs compared against equivalent formulations prepared using conventional organic solvents (Volatile Organic Compounds, or VOCs) is reported. RTILs were found to greatly improve reaction efficiency compared to VOCs whilst maintaining reasonable levels of selectivity. The effect of variables such as RTIL structure, polymerisation temperature and solvent volume on the efficiency and structure of a cocaine-imprinted MIP were investigated and were found to affect polymer properties such as surface morphology, swelling, zeta potential, degree of crosslinking as well as selectivity for the template. Imprinting factors as high as 2.2 were observed for RTIL-prepared MIPs under initial rebinding conditions when using [bmim]BF₄ as polymerisation solvent, compared with the highest imprinting factor of 1.6 for the polymers prepared in CHCl₃. Optimisation of rebinding conditions resulted in ~26% improvement in selectivity for both RTIL and VOC-prepared polymers when using DCM as rebinding solvent. Molecular modelling and NMR analysis of R, S-propranolol-imprinted polymers indicated some interaction between the RTIL anion and the template and monomer, although this was not found to prevent template/monomer associations in the RTIL [bmim]PF₆. [bmim]PF-₆prepared polymers showed good selectivity (imprinting factor of 2.3) and affinity for the template over other compounds, although binding capacity was lower than for the VOC-prepared polymers. The binding capacity for the RTIL-prepared polymers was enhanced through the use of RTILs of increased alkyl chain lengths as polymerisation solvent and by optimisation of rebinding conditions, with the highest imprinting factor of 3.8 observed when rebindings were conducted in methanol.