Use of carbohydrates as initiators for lactone ring-opening polymerization

Our laboratory discovered that, by lipase-catalysis, carbohydrates function as initiators that are regioselectively attached to the carboxyl terminus of propagating chains (Bisht et al, 1998). As an example, a,b-ethylglucopyranoside (EGP) was used as a multifunctional monosaccharide initiator for PPL-catalyzed e-CL ring-opening polymerizations. For an e-CL/EGP ratio of 7:1, in the absence of solvent, a product resulted that had an Mn and Mw/Mn of 2 200 g/mol and 1.3, respectively. Structural analysis by 2-D NMR techniques showed that the reaction was highly regiospecific. In other words, oligo(e-CL) chains formed were attached by an ester group to the primary hydroxyl moiety of EGP. Subsequently, lipase PS-30 catalyzed the selective acrylation of the w-oligo(CL) hydroxyl terminus giving a macromer for free-radical polymerization. Alternatively, acetylation of the w-oligo(CL) hydroxyl terminus resulted in a macroinitiator for lactide ring-opening polymerization. This gave a multi-arm heteroblock copolymer with spatially organized oligo(CL) and oligo(lactide) chain segments.

Scheme 6: αβ-Ethyl glucopyranoside (EGP) initiated ring-opening polymerization of ε-caprolactone and trimethylene carbonate.

Scheme 7. Chemoenzymatic route to spatially defined heteroblock copolymers comprised of oligo(CL) and oligo(lactide) arms.

References

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