Multi-arm star block copolymers based on ε-caprolactone have been prepared by a core-first approach using propoxylated hyperbranched polyglycerol P(G52PO3) as a polyfunctional initiator. Various monomer/initiator ratios were employed in the Sn-catalyzed polymerization in order to vary the length of the caprolactone arms (DPn(arm) = 10 to 50). The molecular weights of the block copolymers were in good aggreement with the calculated values. Careful NMR analysis revealed that the monomer/initiator ratio not only controls the arm length, but also influences the degree of functionalization. Poly(ε-CL) stars with 52 arms and absolute molecular weights between 69 200 and 360 400 g/mol have been prepared. SEC measurements showed that the narrow polydispersity of the core molecule (Mw/Mn = 1.24) could be maintained upon block copolymerization. The resulting star polymers exhibited polydispersities between 1.21 and 1.33.
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Burgath et al. (2000) studied this question.