Synthesis and Micellization Properties of Novel Symmetrical Poly(ε‐caprolactone‐b‐[R,S] β‐malic acid‐b‐ε‐caprolactone) Triblock Copolymers

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AbstractSummary: A four‐step strategy to synthesize well‐defined amphiphilic poly(ε‐caprolactone‐b‐[R,S] β‐malic acid‐b‐ε‐caprolactone) triblock copolymers [P(CL‐b‐MLA‐b‐CL)], which combines the anionic polymerization of [R,S] benzyl β‐malolactonate (MLABz), and the coordination‐insertion ring‐opening polymerization (ROP) of ε‐caprolactone (CL), followed by the selective removal of benzyloxy protective groups of the central poly(malolactonate) block is described. The first step involves MLABz initiated by potassium 11‐hydroxydodecanoate in the presence of 18‐crown‐6 ether. This step was carried out at 0 °C with an initial monomer concentration of 0.2 mol · L−1 in order to limit the occurrence of undesirable transfer and termination reactions by proton abstraction. After selective reduction of the carboxylic acid end‐group of the resulting α‐hydroxy, ω‐carboxylic poly([R,S] benzyl β‐malolactonate) leading to an α,ω‐dihydroxy PMLABz, the polymerization of CL was initiated by each hydroxyl end‐groups previously activated by AlEt3. Finally, after catalytic hydrogenation of the benzyl ester functions, the P(CL‐b‐MLA‐b‐CL) triblock copolymer was recovered and the amphiphilic character evidenced by UV spectroscopy. As demonstrated, the CMC of these new P(CL‐b‐MLA‐b‐CL) triblock copolymer is higher by one order of magnitude than that of a P(MLA‐b‐CL) diblock copolymer of similar composition.Concentration dependence of pyrene I338/I335 intensitiy ratio for P(MLA‐b‐CL) diblock and P(CL‐b‐MLA‐b‐CL) triblock copolymers in water.magnified imageConcentration dependence of pyrene I338/I335 intensitiy ratio for P(MLA‐b‐CL) diblock and P(CL‐b‐MLA‐b‐CL) triblock copolymers in water.