Macromolecules 2008, 41, 5651-5657
5651
Biodegradable Hyperbranched Aliphatic Polyesters Derived from Pentaerythritol Hans R. Kricheldorf* and Gesa Behnken Institut fu¨r Technische and Makromolekulare Chemie, Bundesstr. 45, D-20146 Hamburg, Germany ReceiVed January 28, 2008; ReVised Manuscript ReceiVed April 11, 2008 ABSTRACT: Pentaerythritol (PENT) was polycondensed with dimethyl sebacate (DMS) in bulk at 240 °C. With Ti(OBu)4 as the catalyst, an equimolar feed ratio resulted in gelation even when no vacuum was applied. When the PENT/DMS ratio was raised to 1.2/1.0, soluble viscous resins were obtained, but despite the excess of PENT, the conversion of methyl ester groups never exceeded 92%. With bismuth(III) n-hexanoate (BiHex3) as the catalyst and an 1.0/1.0 feed ratio, nonviscous polyesters were obtained with conversions 1.0), when the reaction conditions are optimized, so that the conversions of methyl ester groups stay e91%. Both 1H NMR and MT mass spectra indicate formation of (hyper) branched polyesters almost free of cyclic structures and with a low content of ether groups, despite high reaction temperatures. Chemical modification of these polyesters is feasible by acylation of the CH2OH groups, and with a large excess of acetic or methacrylic anhydride, even quantitative acylation can be achieved. Functionalization with methacrylate groups yields materials which may act as biodegradable super cross-linkers in radical polymerizations of methacrylates. Such an application may allow, for instance, modification of the mechanical properties of bone cements based on the polymerization of methyl methacrylate. The virgin polyesters having numerous CH2OH groups can easily be cross-linked by means of diisocyanates and, thus, may serve as biodegradable components of coatings. References and Notes (1) Flory, P. J. Chem. ReV. 1946, 39, 137–197. (2) Flory, P. J. “Principles in Polymer Chemistry”; Cornell University Press: Ithaca, NY, 1953; Chapters VII and VIII.
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