Molecularly Imprinted Polymer Colloids Synthesized by Miniemulsion Polymerization for Recognition and Separation of Nonylphenol

Submicronic molecularly imprinted polymer (MIP) colloids were synthesized by polymerization in aqueous dispersed media for selective separation of nonylphenol (NP) organic pollutant. A miniemulsion polymerization process based on ultrasheared monomer droplets has allowed for dispersion of the hydrophobic organic pollutant template to produce water-dispersible colloidal MIP. Structural parameters of the cross-linked polymer particles were tuned during the synthesis to achieve the best compromise between good specificity of imprinted polymer (MIP) sorbent compared to nonimprinted polymer (NIP) (i.e., imprinting factor (alpha)), sufficient level of adsorption capacity (Q), and selectivity of MIP toward the organic pollutant. For that purpose, the polymerization takes place in the organic monomer droplets containing nonylphenol (NP), N-vinylcaprolactam (VCL), different comonomers (vinyl acetate (VAc), vinyl benzoate (VB), or 2-ethylhexanoic acid vinyl ester (VeoVa-EH)), and various contents of divinyl adipate (DVA) cross-linker. Tuning the level of hydrophobic interactions, either by the hydrophobicity of the comonomer (VeoVa-EH > VB > VAc) or by the polarity of the hydroalcoholic mixture used for interfacial adsorption, achieved imprinting factors above unity. The binding of NP follows a monolayer Langmuir adsorption, and the present MIPs selectively recognize NP compared to phenol. Isothermal titration calorimetry (ITC) measurements corroborated both specificity (Delta H-MIP > Delta H-NIP) and selectivity with very low values of binding enthalpy for phenol, p-cresol, and 1-octanol compared to that of NP.