Polydisperse methyl β-cyclodextrin-epichlorohydrin polymers: variable contact time (13)C CP-MAS solid-state NMR characterization.

Isabelle Mallard,Andrea Mele,Franca Castiglione,Enzio Ragg,Walter Panzeri,Davy Baudelet,Monica Ferro

doi:10.3762/bjoc.11.299

Abstract

The polymerization of partially methylated β-cyclodextrin (CRYSMEB) with epichlorohydrin was carried out in the presence of a known amount of toluene as imprinting agent. Three different preparations (D1, D2 and D3) of imprinted polymers were obtained and characterized by solid-state 13C NMR spectroscopy under cross-polarization magic angle spinning (CP-MAS) conditions. The polymers were prepared by using the same synthetic conditions but with different molar ratios of imprinting agent/monomer, leading to morphologically equivalent materials but with different absorption properties. The main purpose of the work was to find a suitable spectroscopic descriptor accounting for the different imprinting process in three homogeneous polymeric networks. The polymers were characterized by studying the kinetics of the cross-polarization process. This approach is based on variable contact time CP-MAS spectra, referred to as VCP-MAS. The analysis of the VCP-MAS spectra provided two relaxation parameters: TCH (the CP time constant) and T1ρ (the proton spin-lattice relaxation time in the rotating frame). The results and the analysis presented in the paper pointed out that TCH is sensitive to the imprinting process, showing variations related to the toluene/cyclodextrin molar ratio used for the preparation of the materials. Conversely, the observed values of T1ρ did not show dramatic variations with the imprinting protocol, but rather confirmed that the three polymers are morphologically similar. Thus the combined use of TCH and T1ρ can be helpful for the characterization and fine tuning of imprinted polymeric matrices.

Highlights

Cyclodextrin polymers are a subject of great interest because of their use in pharmaceutical industry [1,2], analytical chemistry [3,4,5], wastewater treatment [6] and food industry [7,8,9]
We described the synthesis of imprinted polymers
The target molecules form a complex with the cyclodextrin followed by a copolymerization of the imprinted

Summary

Introduction

Cyclodextrin polymers are a subject of great interest because of their use in pharmaceutical industry [1,2], analytical chemistry [3,4,5], wastewater treatment [6] and food industry [7,8,9]. The most efficient method for the synthesis of insoluble polymers is to use di- or polyfunctional linkers with monomers of cyclodextrins. Following a slightly different approach, Trotta [18] and his group demonstrated that polymerization of cyclodextrins with a variety of synthetic equivalents of di- and tetracarboxylic acids provides an easy, efficient and environmentally sustainable route to highly cross-linked, nanoporous polymers commonly referred to as cyclodextrin nanosponges. One of the most frequently used crosslinker for insoluble polymers is epichlorohydrin (EP). In this case, the reaction of β-CD with EP requires very strong alkaline conditions to achieve deprotonation of the hydroxyl groups. EP reacts with the alkoxide to form intra- or inter-ether linkages

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