The development of molecularly imprinted polymers (MIPs) to target polyphenols present in vegetable extracts was here addressed. Polydatin was selected as a template polyphenol due to its relatively high size and amphiphilic character. Different MIPs were synthesized to explore preferential interactions between the functional monomers and the template molecule. The effect of solvent polarity on the molecular imprinting efficiency, namely owing to hydrophobic interactions, was also assessed. Precipitation and suspension polymerization were examined as a possible way to change MIPs morphology and performance. Solid phase extraction and batch/continuous sorption processes were used to evaluate the polyphenols uptake/release in individual/competitive assays. Among the prepared MIPs, a suspension polymerization synthesized material, with 4-vinylpyridine as the functional monomer and water/methanol as solvent, showed a superior performance. The underlying cause of such a significant outcome is the likely surface imprinting process caused by the amphiphilic properties of polydatin. The uptake and subsequent selective release of polyphenols present in natural extracts was successfully demonstrated, considering a red wine solution as a case study. However, hydrophilic/hydrophobic interactions are inevitable (especially with complex natural extracts) and the tuning of the polarity of the solvents is an important issue for the isolation of the different polyphenols.
A recently developed general kinetic approach, based on population balances in terms of generating functions, is applied to the modeling of the molecular architecture of branched copolymers produced through controlled radical polymerization (CRP) techniques, namely nitroxide-mediated radical polymerization (NMRP) and atom-transfer radical polymerization (ATRP). Thanks to this method, it is possible to carry out dynamic predictions of distributions of molecular weights, sequence lengths and z-average mean square radius of gyration of the products, both before and after gelation (whenever it occurs) with consideration of complex kinetic schemes. The model chemical systems styrene + divinylbenzene (S/DVB) and methyl methacrylate + ethylene glycol dimethacrylate (MMA/EGDMA) are experimentally investigated in order to assess the prediction capabilities of the aforementioned approach. Measurements of absolute molecular weights and z-average radius of gyration of the copolymers are performed for different times of polymerization using a SEC system with a refractive index detector coupled with MALLS. It is shown that the proposed computational tool can enhance the possibility of better design of these complex materials but additional studies concerning the impact of intramolecular cyclizations on the structure of materials synthesized at diluted conditions are needed.
10 May 2005 in Macromolecular Theory and Simulations
Summary: Using the authors' previously developed method for the general kinetic analysis of non‐linear irreversible polymerizations, the simulation of free radical homogeneous polymerization systems with terminal branching and chain transfer to polymer has been carried out for continuous stirred tank reactors. Its improved accuracy on the numerical evaluation of generating functions has been exploited in order to perform their numerical inversion and chain length distributions could also be estimated with or without the presence of gel. A comparison with alternative techniques emphasizing the effect of their simplifying assumptions on the accuracy of calculations is also presented. Predicted CLD before gelation (t = 1 h), after gelation (t = 15 h, steady state), and close to gel point for a free radical polymerization with transfer to polymer in a CSTR with τ = 60 min. magnified image Predicted CLD before gelation (t = 1 h), after gelation (t = 15 h, steady state), and close to gel point for a free radical polymerization with transfer to polymer in a CSTR with τ = 60 min.