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Three-arm (A(2)B) and four-arm (A(2)B(2)) star-shaped copolymers based on biocompatible and biodegradable hydrophobic poly(epsilon-caprolactone) (PCL) (A arms) and biocompatible and bioeliminable hydrophilic poly(ethylene oxide) (PEO) (B arms) were synthesized by the coupling of an omega-azide terminated PEO chains with PCL chain bearing one (A(2)B) or two (A(2)B(2)) alkyne functions at the middle of the chain by the copper mediated azide-alkyne cycloaddition (CuAAC). The amphiphilic behavior of these different stars was confirmed by micellization experiments in water followed by dynamic light scattering and transmission electron microscopy analyses. The efficiency to stabilize PLA nanoparticles was investigated in function of the stars structure.

Recent progress in the synthesis of aliphatic polyesters, substituted by pendent functional groups, has been reviewed. Two main strategies have to be distinguished. The first route consists of the ring-opening polymerization of e-caprolactone substituted by various functional groups, protected if needed, in α- or γ-position. In a second strategy, the functional groups are grafted onto preformed polyesters chains in α-position of the carbonyl groups. α-chloro-e-caprolactone is quite an interesting monomer because, after polymerization, the activated chloride can be easily derivatized by atom transfer radical addition and click chemistry, respectively. Similarly, γ-acrylic-e-caprolactone is precursor of (co)polyesters well-suited to derivatization of the pendent double bonds by Michael addition.

The macromolecular engineering of aliphatic polyesters by ring-opening polymerization (ROP) initiated by aluminum alkoxides is now well established. Tin (IV) alkoxides are less popular, mainly because of a poorer control of the chain growth. This paper discusses some recent examples from CERM, showing that tin (IV) alkoxides can advantageously replace the aluminum counterparts as ROP initiators. For instance, they can initiate successfully the Ring-Opening Polymerization of a-chloro-e-caprolactone and dioxepane-2-one. They are also very promising initiators for ROP in supercritical CO 2 and for the synthesis of clay/aliphatic polyester nanocomposites.

The aluminum alkoxide mediated ring opening polymerization of functional lactones, such as γ-ethylene ketal-ϵ-caprolactone (TOSUO), γ-(triethylsilyloxy)-ϵ-caprolactone (SCL) and γ-bromo-ϵ-caprolactone (γBrCL), is a versatile route to polyesters containing ketal, ketone, alcohol and bromide groups. As result of living polyaddition mechanism, random and block copolymerization of ϵCL and γBrCL has been successfully carried out. The reactivity ratios are quite similar (1.08 for ϵ-CL, and 1.12 for γBrCL). These random copolymers are semicrystalline when they contain less than 30 mol% of γBrCL, otherwise they are amorphous. No transesterification reaction occurs during the sequential polymerization of ϵ-CL and γBrCL leading to block copolymers. Reaction of poly(ϵCL-co-γBrCL) with pyridine provides quantitatively a polycationic polyester. Furthermore, the reaction of this random copolymer with 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU) is a route to unsaturated polyesters, whose the non conjugated double bonds can be quantitatively converted into epoxides by reaction with m-chloroperbenzoic acid (mCPBA). No chain degradation is detected during these derivatization reactions of poly(ϵCL-co-γBrCL).