Theophylline molecular imprint composite membranes prepared from poly(vinylidene fluoride) (PVDF) substrate

Theophylline molecular imprint composite membranes were prepared on the PVDF membrane substrate through the free radical polymerization method using theophylline as a template, methacrylic acid (MAA) as a functional monomer, and ethylene glycol dimethacrylate (EDMA) as a cross-linker. The binding constant (K) for the formation of monomer–template adduct was determined by means of infrared spectroscopy titration and nonlinear least-squares method. Theophylline (K=140 M−1) can form more specific binding sites with MAA than caffeine (K=83 M−1), therefore was chosen as the template. An effective ultrasonic cleaning method was used to remove the bound theophylline templates from the polymerized PVDF membrane. The reaction conditions were investigated to optimize the maximum binding capacity of theophylline templates to the PVDF membrane. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and contact angle measurement were used to study the surface chemistry, morphological structure and hydrophilicity of theophylline molecular imprint composite membranes. The specific binding capacities of theophylline imprint membranes were investigated by both single molecule and multi-molecule solution filtration experiments, respectively.