Novel Chemical Architectures Based on Beta-Cyclodextrin Derivatives Covalently Attached on Polymer Spheres

Abstract

This study presents the synthesis and characterization of polymer derivatives of beta-cyclodextrin (BCD), obtained by chemical grafting onto spherical polymer particles (200 nm) presenting oxirane functional groups at their surface. The polymer spheres were synthesized by emulsion polymerization of styrene (ST) and hydroxyethyl methacrylate (HEMA), followed by the grafting on the surface of glycidyl methacrylate (GMA) by seeded emulsion polymerization. The BCD-polymer derivatives were obtained using two BCD derivatives with hydroxylic (BCD-OH) and amino groups (BCD-NH₂). The degree of polymer covalent functionalization using the BCD-OH and BCD-NH₂ derivatives were determined to be 4.27 and 19.19 weight %, respectively. The adsorption properties of the materials were evaluated using bisphenol A as a target molecule. The best fit for the adsorption kinetics was Lagergren's model (both for Q_e value and for R²) together with Weber's intraparticle diffusion model in the case of ST-HEMA-GMA-BCD-NH₂. The isothermal adsorption evaluation indicated that both systems follow a Langmuir type behavior and afforded a Q_max value of 148.37 mg g^-1 and 37.09 mg g^-1 for ST-HEMA-GMA-BCD-NH₂ and ST-HEMA-GMA-BCD-OH, respectively. The BCD-modified polymers display a degradation temperature of over 400 °C which can be attributed to the existence of hydrogen bonds and BCD thermal degradation pathway in the presence of the polymers.

Keywords: adsorption isotherms; adsorption kinetics; beta-cyclodextrin; bisphenol A adsorption; emulsion polymerization.

Scheme 1

Synthesis route for BCD-NH₂.

Scheme 2

Chemical synthesis of ST-HEMA-GMA-BCD-NH₂. (a) The reaction of BCD-NH₂ with ST-HEMA-GMA; (b) ST-HEMA-GMA-BCD-NH₂ complex structure (3D).

Figure 1

TEM images of the samples: (a) ST-HEMA; (b) ST-HEMA-GMA; (c) ST-HEMA-GMA-BCD-NH₂ and (d) ST-HEMA-GMA-BCD-OH.

Figure 2

FT-IR spectra for ST-HEMA, BCD-NH₂, ST-HEMA-GMA-BCD-NH₂, ST-HEMA-GMA-BCD-OH, ST-HEMA-GMA, ST-HEMA. (a)ST-HEMA; ST-HEMA-GMA; (b) BCD-NH₂; ST-HEMA-GMA; Pol-BCD-NH₂; Pol-BCD-OH.

Figure 3

Adsorption kinetic curve of ST-HEMA-GMA-BCD-NH₂ at pH 5 and 25 °C.

Figure 4

The linear plots of Lagergren’s pseudo-first-order (A), Ho’s pseudo-second-order (B), and Weber’s intraparticles diffusion models (C).

Figure 5

(A,C) Langmuir plots illustrating the linear dependences of 1/Q_e on 1/c_e, and (B,D) Freundlich plot illustrating the linear dependences of lnQ_e on lnc_e for adsorption of bisphenol A by ST-HEMA-BCD-NH₂ and ST-HEMA-BCD-OH, respectively.

Figure 6

(a) TGA curves for BCD-NH₂, BCD-OH, ST-HEMA-GMA-BCD-NH₂, ST-HEMA-GMA-BCD-OH, ST-HEMA-GMA, ST-HEMA and (b) DTG curves for BCD-NH₂, BCD-OH, ST-HEMA-GMA-BCD-NH₂, ST-HEMA-GMA-BCD-OH, ST-HEMA-GMA, ST-HEMA.