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 vario us numbers of arms with a fixed molecular weight (MW similar to 10 000) wer e synthesized by anionic polymerization of ethylene oxide initiated with me talated plurifunctional initiators and used asa core block. The star-shaped block. copolymers were prepared by ring-opening polymerization of L-lactid e or epsilon-caprolactone in the presence of multiarm PEOs and a catalytic amount of stannous octoate. The equilibrium swelling and thermal and soluti on properties of the synthesized star-shaped polymers were examined. The bl ock 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 te ndency in solution viscosity of the starshaped PEO and block copolymers was found. The results obtained in this study revealed unique properties of st ar-shaped block polymers which could be useful in the formulation of delive ry carrier for polypeptide.