Understanding the Impact of Reaction Parameters on Macromolecular Structure, and the Binding and Transport Properties of Imprinted Crosslinked Polymers

Abstract

Molecular imprinting is the design and synthesis of polymer networks that can recognize a template molecule and bind it preferentially in solution. Selective binding of template combined with stability and cost effectiveness make them attractive for a wide variety of applications. In this work, molecularly imprinted, crosslinked poly(methacrylic acid-co-ethylene glycol dimethacrylate) or poly(MAA-co-EGDMA) and poly(hydroxyethyl methacrylate-co-diethylaminoethyl methacrylate-co-poly(ethyleneglycol200) dimethacrylate) or poly(HEMA-co-DEAEM-co-PEG200DMA) networks were synthesized and characterized to better understand the effect of various reaction parameters on their macromolecular structure and subsequently their binding and transport properties. Conventional free radical polymerization (FRP) as well as iniferter mediated living radical polymerization (LRP) was used for polymer synthesis. LRP offers the ability to create improved imprinted polymers with more homogeneous networks and, as a result, better binding parameters. The use of LRP resulted in quadrupling of the number of binding sites in highly crosslinked imprinted poly(MAA-co-EGDMA) polymers; and a tripling of the number of binding sites in weakly crosslinked imprinted poly(MAA-co-EGDMA) gels. Analysis of the polymerization reaction revealed that the observed increase in binding parameters of the polymers could be explained by the extension of the reaction-controlled regime during propagation. LRP was shown to have extended propagation in polymerization reactions which subsequently resulted in more monodisperse polymer chains and more homogenous imprinted polymer networks with better template binding characteristics. Weakly crosslinked poly(HEMA-co-DEAEM-co-PEG200DMA) gels imprinted with diclofenac sodium, an anti-inflammatory drug, and prepared via LRP demonstrated significantly higher drug binding as well as slower drug release rates as compared to corresponding gels prepared via FRP. In addition, the effects of varying reaction parameters, such as, template concentration, functional monomer concentration, presence of solvent, and degree and length of crosslinking, on the template binding and transport properties of the imprinted polymer gels was examined. Varying the reaction parameters had diverse effects on the polymer properties. For example, an increase in template concentration was shown to result in increased template binding and slower template release rates while an increase in the degree of crosslinking resulted in decreased template binding and template release rates. It was also shown that the use of LRP had a more significant impact than any other reaction parameter. Finally, the use of LRP in the formation of molecularly imprinted polymers was shown to result in significant improvements in the template binding and transport properties of the resulting polymers due to the improved network architecture of the molecularly imprinted polymers. In addition the ability to create imprinted polymer gels with high drug binding capacity and extended, tailorable and controlled drug release by combining LRP with variations in other reaction parameters was demonstrated.