Polyesters such as Poly(lactide), Poly(ε-caprolactone) or Poly(glycolide) are most widely utilized polymers in the field of biomedical applications with regard to their biocompatibility and biodegradability. In general PLA attracts increasing interest because of its convenient accessibility from renewable resources with regard to environmental and economic aspects. One major scientific demand is to tailor the materials properties by copolymerization with different comonomers or by variation of the polymer architecture (e.g. block, star-shaped, branched macromolecules). In recent years especially the introduction of branches into the polymer structure afforded materials with unusual characteristics.
Figure 1: Soluble Hyperbranched Poly(glycolide) Copolymers2
Hyperbranched polyester copolymers are accessible by copolymerization of cyclic lactones together with bishydroxy-acids as AB2-monomers1,2 or with hydroxy-functional inimers3 employing metal-/enzyme-catalyzed ring-opening polymerization or polycondensation.
Figure 2: Branched and Hyperbranched Poly(L-lactide) Copolymers3
Multi-arm star polymers are an interesting class of macromolecules due to the significantly altered physical properties in contrast to their linear analogs. Apart from this aspect star polymers with a hydrophilic multifunctional core have attracted increasing interest for the fabrication of amphiphilic core-shell structures. A suitable multifunctional core is hydrophilic hyperbranched polyglycerol which has been functionalized with polyglycolide and polylactide arms by a "grafting-from" approach.4,5
Figure 3: Poly(glycolide) multi-arm star polymers4
Linear aliphatic polyesters represent convenient building blocks for the formation of hydrophobic domains in amphiphilic block copolymers because of their degradability and nontoxicity. PIGMA-b-PLLA copolymers were synthesized by atom transfer radical polymerization (ATRP) of an acetal-protected glycerol monomethacrylate monomer and concurrent organo-base catalyzed ROP of L-lactide.4 The uniformly shaped micelles exhibit promising potential as biomedical devices in drug delivery and controlled release systems.6
Figure 4: Poly(IGMA)-b-poly(D- or L-lactide) Copolymers6
References
| [1] | "Enzyme-Catalyzed Synthesis of Hyperbranched Aliphatic Polyesters" S. Skaria, M. Smet, H. Frey, Macromol. Rapid Commun. 2002, 23, 292–296. DOI: 10.1002/1521-3927(20020301)23:4<292::AID-MARC292>3.0.CO;2-5. |
| [2] | "Soluble Hyperbranched Poly(glycolide) Copolymers" A. M. Fischer, H. Frey, Macromolecules 2010, 43, 8539–8548. DOI: 10.1021/ma101710t. |
| [3] | "Inimer-Promoted Synthesis of Branched and Hyperbranched Polylactide Copolymers" F. K. Wolf, H. Frey, Macromolecules 2009, 42, 9443–9456. DOI: 10.1021/ma9016746. |
| [4] | "Poly(glycolide) multi-arm star polymers: Improved solubility via limited arm length" F. K. Wolf, A. M. Fischer, H. Frey, Beilstein J. Org. Chem. 2010, 6, 67. DOI: 10.3762/bjoc.6.67. |
| [5] | "Multi-Arm Star Poly(L-lactide) with Hyperbranched Polyglycerol Core" C. Gottschalk, F. Wolf, H. Frey, Macromol. Chem. Phys. 2007, 208, 1657–1665. DOI: 10.1002/macp.200700168. |
| [6] | "Poly(isoglycerol methacrylate)- b -poly(d or l -lactide) Copolymers: A Novel Hydrophilic Methacrylate as Building Block for Supramolecular Aggregates" F. K. Wolf, A. M. Hofmann, H. Frey, Macromolecules 2010, 43, 3314–3324. DOI: 10.1021/ma902844m. |