Ability to control the glass transition temperature of amorphous shape-memory polyesterurethane networks by varying prep
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Ability to control the glass transition temperature of amorphous shape-memory polyesterurethane networks by varying prepolymers in molecular mass as well as in type and content of incorporated comonomers J. Zotzmann1, S. Kelch2, A. Alteheld3, M. Behl1 and A. Lendlein1 1 Center for Biomaterial Development, GKSS Research Center Geesthacht GmbH, D-14513 Teltow, Germany 2 Sika Technology AG, Tüffenwies 16, CH-8048 Zurich, Switzerland and 3 BASF Aktiengesellschaft, Carl-Bosch-Str. 38, D-67056 Ludwigshafen, Germany ABSTRACT The need of intelligent implant materials for applications in the area of minimally invasive surgery leads to tremendous attention for polymers which combine degradability and shapememory capability. Application of heat, and thereby exceeding a certain switching temperature Tsw, causes the device to changes its shape. The precise control of Tsw is particularly challenging. It was investigated how far the glass transition temperature Tg of amorphous polymer networks based on star-shaped polyester macrotetrols crosslinked with a low-molecular weight linker can be controlled systematically by incorporation of different comonomers. The molecular weight of the prepolymers as well as type and content of the comonomers was varied. The Tg could be adjusted by selection of comonomer type and ratio without affecting the advantageous elastic properties of the polymer networks. INTRODUCTION Aliphatic (co)polyesters are used today in numerous medical applications such as degradable polymeric implant materials for surgical devices and drug release systems.[1-3] The combination of degradability with the shape-memory capability resulting in multifunctional polymers is motivated by the aim to insert spacious degradable implants through small incisions into the body[4] or to manipulate their shape on demand during a minimally-invasive procedure.[5,6] The shape-memory effect enables a bulky device to be programmed into a compressed temporary shape. In the thermally induced shape-memory effect, at Tsw the device recovers its original shape. According to various application strategies, Tsw must be adjustable in different temperature ranges. If Tsw ranges between room temperature and body temperature the thermally-induced shape change occurs automatically after implantation. However, a Tsw slightly above body temperature enables on demand control of the shape change. Here, the heat is applied either indirectly through IR-irradiation or directly by application of an external heating medium. Tsw of amorphous polymers is related to Tg of the switching domain. Previous investigations showed the possibility of controlling Tsw and the hydrolytic degradation rate of a shape-memory polymer network with crystallizable switching segments where Tsw was related to the melting point Tm of the switching phase.[7] Alteration of the macromolecular architecture to completely amorphous polymer networks allows a broadened adjustability of morphology and mechanical properties. Unlike semi-crystalline polymers these materials show
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