Star-shaped poly(ether-ester) block copolymers: Synthesis, characterization, and their physical properties

Biodegradable polymers based on star-shaped poly(ethylene oxide) (PEO)-poly(L-lactide) (PLA) and PEO-poly(epsilon-caprolactone) (PCL) block copolymers were synthesized by a divergent synthetic method. Multiarm PEOs with various numbers of arms with a fixed molecular weight (MW similar to 10 000) were synthesized by anionic polymerization of ethylene oxide initiated with metalated plurifunctional initiators and used asa core block. The star-shaped block. copolymers were prepared by ring-opening polymerization of L-lactide or epsilon-caprolactone in the presence of multiarm PEOs and a catalytic amount of stannous octoate. The equilibrium swelling and thermal and solution properties of the synthesized star-shaped polymers were examined. The block copolymers were swollen in distilled water, and the degree of swelling decreased as the number of arms increased. The melting point, crystallinity, and phase separation decreased with the degree of branching. A similar tendency in solution viscosity of the starshaped PEO and block copolymers was found. The results obtained in this study revealed unique properties of star-shaped block polymers which could be useful in the formulation of delivery carrier for polypeptide.