Shape-memory Polymer Networks from Oligo[(epsilon-hydroxycaproate)-co-glycolate]-dimethacrylates and Butylacrylate with Adjustable Hydrolytic Degradation Rate

Abstract

Degradable shape-memory polymer networks intended for biomedical applications were synthesized from oligo[(-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 Tm between 18 and 53 C which can be used as switching transition for the shape-memory effect can be attributed to the crystalline poly(-hydroxycaproate) phase. At temperatures below Tm the elastic properties are dominated by these physical cross-links. At temperatures higher than Tm 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 Mn of up to 13 500 g·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 C show that the degradation rate can be accelerated by increasing the glycolate content and decelerated by the incorporation of n-butyl acrylate.