Shape-Memory Polymer Networks Prepared from Star-Shaped Poly[(L-lactide)-co-glycolide] Precursors


Amorphous degradable copolymer networks such as poly[(L-lactide)-co-glycolide] (PLGA) are promising multifunctional polymers with tailorable degradation profiles and capable of a thermally-induced shape-memory effect. Currently, the shape-memory performance for covalently crosslinked networks based on linear PLGA dimethacrylate precursors (cPLGA) is limited. In this study we explored the shape-memory properties of cPLGA networks prepared from three-armed 2-isocyanatoethyl methacrylate functionalized precursors via photopolymerization. cPLGA exhibited excellent dual-shape properties characterized by an almost complete fixation of the temporary shape as well as an almost perfect recovery of the original shape. In the dry state cPLGA exhibited a switching temperature (Tsw) of 60 °C with a narrow recovery temperature interval of ΔTrec = 5 °C, while a significant lower Tsw of 40 °C with a ΔTrec = 15 °C was obtained when the polymer network was investigated in an aqueous environment. A concomitant decrease in the glass transition temperature could be observed in differential scanning calorimetry heating curves for copolymer networks after storage in aqueous buffer solution at 37 °C for 7 days, which can be attributed to the up-take of water molecules (1.5 wt%). The shape-memory properties achieved for cPLGA, in particular the shape recovery ratio and ΔTrec were superior to those of analogous polymer networks based on linear PLGA dimethacrylates.
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