The synthesis, characterization, and polymerization of a new cyclic ester, γ-bromo-ε-caprolactone (γBrCL), are reported. The ring-opening polymerization (ROP) of this new monomer initiated from Al(OiPr)3 as initiator in toluene at 0 °C was found to be living and proceeds by a coordination−insertion mechanism. Random and block copolymerizations of this γBrCL with ε-caprolactone (εCL) were also found to be living as evidenced by the experimental molecular weight which is consistent with that expected from the monomer to initiator molar ratio, the narrow polydispersity, and the good agreement between the comonomers molar fraction in the comonomer feed and the copolymer. The thermal transitions (T g and T m) in the εCL/γBrCL random copolymers depend strongly on the γBrCL content. Increasing the γBrCL content in the copolymer (F BrCL) increased the T g of the copolymer from −61 °C for poly(ε-caprolactone) to −16.5 °C for the PγBrCL homopolymer but decreased the T m of the PCL to contents of ∼ 30 mol % of γBrCL (F BrCL = 0.3). Beyond this value, the copolymers were found to be amorphous and exist as viscous liquids.

The ring-opening polymerization of ε-caprolactone (CL) initiated by dibutyltin dimethoxide was studied in supercritical carbon dioxide at 40 °C, under a pressure of 210−215 bar. The polymerization is controlled as assessed by the linear dependence of M n,SEC on conversion and of ln([CL]0/[CL]) on time. Moreover, there is a good agreement between M n,SEC and M n,calc, at least until 20 000 g/mol. The apparent rate constants of polymerization in different media increase as follows: sc CO2, CFC-113, toluene, bulk. The kinetic order in initiator for the polymerization in solution and in sc CO2 was extracted from the slope of ln k app vs ln [Sn]0. It appears to depend on the initiator concentration in solution, which is not the case in sc CO2.

New functional aliphatic polyesters were prepared by chemical modification of brominated copolyesters. Poly( -caprolactone)-co-poly(γ-(2-bromo-2-methylpropionate)--caprolactone) copolymer was prepared and successfully converted into copolyester bearing methacrylate double bonds by dehydrohalogenation of the pendant tertiary alkyl bromides, thus leading to cross-linkable polyester. The tertiary alkyl bromide groups of the original copolyester were also quaternized by reaction with pyridine, although some side reactions occurred which limited the reaction yield. Nevertheless, quaternization of the bromide groups of the poly( -caprolactone)-co-poly(γ-bromo--caprolactone) copolymer proved to be quantitative and to occur without degradation of the polyester chains. This general strategy paves the way to either amphiphilic copolyesters or water-soluble polyesters. The poly( -caprolactone)-co-poly(γ-bromo--caprolactone) copolymer was also quantitatively converted into unsaturated copolyester by dehydrohalogenation with formation of double bonds including acrylic-type double bonds. As an alternative, γ-bromo-caprolactone was first dehydrohalogenated, and the unsaturated cyclic monomer was copolymerized with -caprolactone. Finally, the nonconjugated double bonds of the copolyesters were oxidized into epoxides, except for the acrylic-type unsaturations which remained unchanged.

Fully biodegradable and surface-functionalized poly(D,L-lactide) (PLA) nanoparticles have been prepared by a co-precipitation technique. Novel amphiphilic random copolyesters P(CL-co-gammaXCL) were synthesized by controlled copolymerization of epsilon-caprolactone and epsilon-caprolactone substituted in the gamma-position by a hydrophilic X group, where X is either a cationic pyridinium (gammaPyCL) or a non-ionic hydroxyl (gammaOHCL). Nanoparticles were prepared by co-precipitation of PLA with the P(CL-co-gammaXCL) copolyester from a DMSO solution. Small amounts of cationic P(CL-co-gammaPyCL) copolymers are needed to quantitatively form stable nanoparticles (ca. 10 mg/ 100 mg PLA), although larger amounts of non-ionic P(CL-co-gammaOHCL) copolymers are needed (> or = 12.5 mg/ 100 mg PLA). Copolymers with a low degree of polymerization (ca. 40) are more efficient stabilizers, probably because of faster migration towards the nanoparticle-water interface. The nanoparticle diameter decreases with the polymer concentration in DMSO, e.g. from ca. 160 nm (16 mg/ml) to ca. 100 nm (2 mg/ml) for PLA/P(CL-co-gammaPyCL) nanoparticles. Migration of the P(CL-co-gammaXCL) copolyesters to the nanoparticle surface was confirmed by measurement of the zeta potential, i.e. ca. +65 mV for P(CL-co-gammaPCL) and -7 mV for P(CL-co-gammaOHCL). The polyamphiphilic copolyesters stabilize PLA nanoparticles by electrostatic or steric repulsions, depending on whether they are charged or not. They also impart functionality and reactivity to the surface, which opens up new opportunities for labelling and targeting purposes.

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