Synthesis And Characterization Of Fluoroalkyl End-Capped Block Copolymers With PH/Temperature Response And Their Self-Assembly Behavior

A series of fluoroalkyl end-capped diblock copolymers of poly[2-(N,N- dimethylamino)ethyl methacrylate] (PDMAEMA or PDMA) and poly[2-(N,N-diethylamino)ethyl methacrylate] (PDEAEMA or PDEA) have been synthesized via oxyanion-initiated polymerization, in which a potassium alcoholate of 4,4,5,5,6,6,7,7,7-nonafluoro-1-heptanol (NFHOK) was used as an initiator. The chemical structures of the NFHO-PDMA-b-PDEA and NFHO-PDEA-b-PDMA depended on the addition sequence of the two monomers and the feeding molar ratios of [DMA] to [DEA] during the polymerization process. These copolymers have been characterized by 1H NMR and 19F NMR spectroscopy and gel permeation chromatography (GPC). The aggregation behavior of these copolymers in aqueous solutions at different pH media was studied using a combination of surface tension, fluorescence probe, and transmission electron microscopy (TEM). Both diblock copolymers exhibited distinct pH/temperature-responsive properties. The critical micelle concentrations (cmcs) of these copolymers have been investigated, and the results showed that these copolymers possess excellent surface activity. Besides, these fluoroalkyl end-capped diblock copolymers showed pH-induced lower critical solution temperatures (LCSTs) in water. TEM analysis indicated that the NFHO-PDMA30-b-PDEA10 diblock copolymers can self-assemble into the multicompartment micelles in aqueous solutions under basic conditions, in which the pH value is higher than the pKa values of both PDMA and PDEA homopolymers, while the NFHO-PDEA10-b-PDMA30 diblock copolymers can form flowerlike micelles in basic aqueous solution. Because both PDMA and PDEA blocks can be protonized in acidic media, no aggregation of the copolymers could be observed by TEM. With the gradual increase of pH value to 9.0, the multicompartment micelles formed. But the morphologies of the micelles were different from the mentioned above.TEM and Steady-State Fluorescence Measurements results indicated that the salts and component and properties of solvent effect greatly on the morphologies of self-assemble micelles.