Synthesis And Characterization Of ABC-type Amphiphilic Triblock Copolymers

(1) Well-defined ABC-type pH-responsive fluorinated block copolymers composed of poly[2-(N, N-dimethylamino)ethyl methacrylate] (PDMAEMA or PDMA), poly[2-(N, N-diethylamino)ethyl methacrylate] (PDEAEMA or PDEA) and poly(2, 2, 3, 3, 4, 4, 5, 5-octafluoropentyl methacrylate) (POFPMA) have been synthesized via oxyanion-initiated polymerization, in which benzyloxy anion (BzO-) was used as the initiator. The chemical structures, molecular weight and molecular weight distribution of PDMA-b-PDEA-b-POFPMA and PDEA-b-PDMA-b-POFPMA triblock copolymers with the same components but different block sequence were characterized by 1H NMR, 19F NMR and GPC. The self-assembly behavior of copolymers in aqueous solution with different pH values was demonstrated by the combination of surface tension, fluorescence probe method, zeta potential, light scattering and transmission electron microscopy.(2) The second part of this paper describes the synthesis of novel ABC-type pH-responsive double hydrophilic block copolymers, poly(ethylene glycol)-b-poly(methacrylic acid)-b-poly[2-(N, N- dimethylamino)ethyl methacrylate] (mPEG-b-PMAA-b-PDMA), and their stimuli responsiveness at different pH media to form three core-shell aggregates. First, poly(ethylene glycol) monomethyl ether reacted with potassium hydride to yield an oxyanion (mPEG-O?K+) as a macroinitiator, and then two monomers, butyl methacrylate and 2-(dimethylamino)ethyl methacrylate, were added into the reaction system in sequence. The produced mPEG-b-PtBMA-b-PDMA triblock copolymers were then transferred into mPEG-b-PMAA-b-PDMA triblock copolymers via hydrolysis to transfer the hydrophobic PtBMA blocks into hydrophilic PMAA blocks. The pH-responsive aggregation behavior of mPEG-b-PMAA-b-PDMA triblock copolymers in aqueous solution was investigated by a combination of 1H NMR, Dynamic Light Scattering (DLS), surface tension, zeta potential and transmission electron microscopy (TEM). At pH 3.0, the aggregating particles in form of PMAA/mPEG core and PDMA shell can be ascribed to the hydrogen bonding between carboxyl groups and methoxy groups. In contrast, PDMA was became a hydrophobic block at pH 10.0, and give aggregating particles with PDMA core and mPEG/PMAA shell. Very interestingly, a complex core based on the oppositely charged interaction between PDMA and PMAA can be found at pH 8.0 with mPEG as shell. Finally, the–COOH groups in mPEG-b-PMAA-b-PDMA were partially changed into thiol groups (-SH) via polymer reaction, and the latter was oxidized to form bridging disulfide linkages, which can stabilize above-mentioned aggregating particles to fabricate core-crosslinking or shell-crosslinking particles. The properties of these corresponding cross-linked micelles were investigated by Dynamic Light Scattering (DLS).