Novel Stoichiometric, Noncovalent Pinacolyl Methylphosphonate Imprinted Polymers: A Rational Design by NMR Spectroscopy

Abstract

The stoichiometric noncovalent imprinting of pinacolyl methylphosphonate (PMP), a degradation product of a chemical warfare agent, has been investigated. A rational approach consisting of controlling the number of specific sites produced during the polymerization was carried out in order to design the methacrylic acid (MAA)-based imprinted polymers. The objective of the method was to study by NMR spectroscopy the molecular association process between the monomer (MAA) and the template (PMP) in solution. Accurate variations in the chemical shifts of 1 H and 13 C were determined in a series of samples at various concentrations in the mixture of acetonitrile/toluene (3:1, v/v). By using an elaborated data treatment, we were able to simultaneously determine the stoichiometry, the association constant, and the condensation degree of the resulting complex. On the basis of these results, a stoichiometric noncovalent PMP-imprinted polymer was subsequently synthesized. Adsorption isotherms of the materials were measured and confronted with those of an imprinted polymer conventionally synthesized with excess monomer. These results established for the first time, the feasibility of imprinted polymers with low-molecular-weight and poorly functionalized templates such as pinacolyl methylphosphonate via stoichiometric noncovalent interactions. Batch binding tests were also carried out on a series of three analogue phosphonates in order to elucidate the influence of the functionality, shape, and size of the analyte on the adsorption properties of the polymers.