Positron annihilation lifetime spectroscopy of molecularly imprinted hydroxyethyl methacrylate based polymers

Abstract

Radiation-induced molecular imprinting of d-glucose onto poly(2-hydroxyethyl methacrylate) (HEMA) matrix was achieved to create three-dimensional cavities to recognize and bind glucose. Molecularly imprinted polymers (MIPs) were synthesized with different types of crosslinkers and varying amounts of template molecule in an attempt to elucidate the impact of imprint quantities on the effectiveness of imprinting technique. The crosslinking agents used in this study were diethylene glycol diacrylate (DEGDA), triethylene glycol dimethacrylate (TEGDMA) and polypropylene glycol dimethacrylate (PPGDMA) in the order of increasing chain length. Crosslinking agent concentration in the polymerization mixture (monomer, crosslinking agent and template) covered a range of 10, 20, 30, and 70 mol%. The mole ratio of template molecule, d-glucose to functional monomer, HEMA, was kept either as 1:3 or 1:6. The absorbed dose varied from 1 to 15 kGy. Control polymers were synthesized with exactly the same composition in the absence of d-glucose. Cavity sizes of MIPs were investigated by positron annihilation lifetime (PAL) measurements. A sandwich arrangement (sample–source–sample) was used. PAL experiments were carried out using a conventional fast–fast coincidence system having a time resolution (FWHM) of about 280 ps. Free-volume hole radii of samples were investigated in their dry and fully water swollen state. The results obtained from a systematic study of the effects of concentration and molecular size of the crosslinking agents, template to monomer ratio and irradiation dose experiments suggest that control of cavity size is feasible in nanometer scale by the optimization of these parameters revealed by means of (PAL) spectroscopy technique.