(250f) Highly Selective Enzymatic Ring-Opening Polymerization: Syntheses and Characterizations of Thermoplastic Di-Block Co-Polyesters Containing Poly[(R)-3-Hydroxybutyrate] and Poly(å-Caprolactone) Blocks

Enzymatic ring-opening polymerization provides with a green and selective tool for the preparation of biodegradable polymers such as polyesters and polycarbonates [1-2]. We recently explored the use of a telechelic macro-diol containing a primary and a secondary OH end groups, derived from microbial poly[(R)-3-hydroxybutyrate] (PHB), as an initiator for the lipase-catalyzed ring-opening polymerization of å-caprolactone (CL).[3] The enzymatic reaction was highly selective: the primary OH end group of PHB-diol was found to initiate the ring-opening polymerization of å-caprolactone, while the secondary OH end group was not reacted thus remaining as an end group of the final di-block polymer; no enzymatic transesterification of PHB-diol and PCL happened; and no random co-polymers formed during the polymerization. Optimal enzymatic polymerization conditions were established for the preparation of block co-polymers with different block ratio and different molecular weight. Novel di-block co-polyesters containing PHB and PCL blocks were synthesized in 69-90% yield and their structures were established by IR, 1H-NMR and 13C-NMR analyses. Incorporation of PCL into PHB significantly improved the thermoplastic properties of the polymers: poly(HB-co-CL)s with 44-74%(wt/wt) PCL demonstrated a Tg of about -60°C and Tm of 120-149°C and 50-54°C, being potentially useful thermoplastic biomaterials. The non-toxic and selective enzymatic ring-opening polymerization provides with new method for the modification of microbial polyesters as biocompatible materials and for the preparation of di-block co-polymers with novel structures and functional end groups.

References:

[1] Gross, R. A.; Kumar, A.; Kalara, B. Chem. Rev. 2001, 101, 2097.

[2] Kobayashi, S.; Uyama, H.; Kimura, S. Chem. Rev. 2001, 101, 3793.

[3] Dai, S.; Li, Z. Biomacromolecules, 2008, in press.