Irradiation-initiated monolayer polymerization

Figure 33 PSP micrographs of a structured PS film, prepared by partial ablation of the initiator monolayer followed by thermal polymerization at 60°C for 4 h (styrene/toluene 1 1 v/v) (a) micrograph taken at resonance angle of the irradiated areas (48.2°) (b) micrograph taken at resonance angle of the polymer modified areas (55.2°, 15.7 mn PS).

MIP films, applied to a QCM transducer, have been employed for chiral recognition of the R- and 5-propranolol enantiomers [107]. MIP films were prepared for that purpose by surface grafted photo-radical polymerization. First, a monolayer of 11-mercaptoundecanoic acid was self-assembled on a gold electrode of the quartz resonator. Then, a 2,2 -azobis(2-amidinopropane) hydrochloride initiator (AAPH), was attached to this monolayer. Subsequently, this surface-modified resonator was immersed in an ACN solution containing the MAA functional monomer, enantiomer template and trimethylolpropane trimethacrylate (TRIM) cross-linker. Next, the solution was irradiated with UV light for photopolymerization. The resulting MIP-coated resonator was used for enantioselective determination of the propranolol enantiomers under the batch [107] conditions and the FIA [107] conditions with an aqueous-ACN mixed solvent solution as the carrier. The MIP-QCM chemosensor was enantioselective to 5-propranolol at concentrations exceeding 0.38 mM [107]. 

In an elegant experiment, Niwa and coworkers prepared a mixed monolayer by codepositing asymmetrical disulphides 14 and 15 in the ratio 200 1. The xanthate groups in disulphide 15 serves as a photo-initiator. Irradiation of the film results in the polymerization of the styrene moieties as seen by cyclic voltammetry. Virtually no polymerization occurs in the single-component monolayer of 14, which proves the importance of having a photo-initiator in the film346,347. 

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