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  • Title: Shape-memory polymer networks from oligo[(epsilon-hydroxycaproate)-co-glycolate]dimethacrylates and butyl acrylate with adjustable hydrolytic degradation rate.
    Author: Kelch S, Steuer S, Schmidt AM, Lendlein A.
    Journal: Biomacromolecules; 2007 Mar; 8(3):1018-27. PubMed ID: 17305394.
    Abstract:
    Degradable shape-memory polymer networks intended for biomedical applications were synthesized from oligo[(epsilon-hydroxycaproate)-co-glycolate]dimethacrylates with glycolate contents between 0 and 30 mol % using a photopolymerization process. In addition AB copolymer networks were prepared by adding 60 wt % n-butyl acrylate as comonomer. All synthesized polymer networks are semicrystalline at room temperature. A melting transition T(m) between 18 and 53 degrees C which can be used as switching transition for the shape-memory effect can be attributed to the crystalline poly(epsilon-hydroxycaproate) phase. At temperatures below T(m) the elastic properties are dominated by these physical cross-links. At temperatures higher than T(m) the E modulus of the amorphous polymer networks is lowered by up to 2 orders of magnitude, depending on the chemical cross-link density. Copolymer networks based on macrodimethacrylates with a M(n) of up to 13,500 g x mol(-1) and a maximum glycolate content of 21 mol % show quantitative strain recovery rates in stress-controlled cyclic thermomechanical experiments. Hydrolytic degradation experiments of polymer networks performed in phosphate buffer solution at 37 degrees C show that the degradation rate can be accelerated by increasing the glycolate content and decelerated by the incorporation of n-butyl acrylate.
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