Design of semi-interpenetrating networks based on poly(ethyl-2-cyanoacrylate) and oligo(ethylene glycol) diglycidyl ethe
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Design of semi-interpenetrating networks based on poly(ethyl-2-cyanoacrylate) and oligo(ethylene glycol) diglycidyl ether G. Tripodo, C. Wischke, and A. Lendlein Center for Biomaterial Development and Berlin-Brandenburg Center for Regenerative Therapies, Institute of Polymer Research, Helmholtz-Zentrum Geesthacht, Kantstrasse 55, 14513 Teltow, Germany. ABSTRACT The synthesis of semi-interpenetrating networks (SIPN) based on linear poly(ethyl 2cyanoacrylate) (PECA) and oligo(ethylene glycol) diglycidyl ether (OEGDG) based polymer networks was motivated by the hypothesis that the brittleness of polycyanoacrylates may be overcome by incorporating them into a polymer network architecture. A sequential synthetic route was applied, in which first PECA was prepared by anionic polymerization. Subsequently, OEGDG was crosslinked with different anhydrides and curing catalysts to form networks with hydrolyzable ester bonds and interpenetrating PECA. These SIPNs showed a low water uptake compared to other polyether based networks. Some of the obtained materials were transparent and exhibited a great flexibility, which was maintained also after 24 h of immersion in water and subsequent drying. Such networks could be components of future stimuli-sensitive material systems. INTRODUCTION Poly(alkyl-2-cyanoacrylate)s (PACAs) are degradable and biocompatible linear polymers. However, their extensive use as biomaterials is limited by their hydrophobicity and poor flexibility [1]. Brittleness of PACAs is linked to their high glass transition temperature Tg, e.g., 146 °C for PECA [2] or 118 °C for poly(n-butyl-2-cyanoacrylate)[3]. Recently, a number of design strategies for obtaining elastic PACAs were reported in the literature, but none of them succeed. For instance, blending PECA with oligo(ethylene glycol) diglycidyl ether (OEGDG) resulted in highly flexible materials [2]. However, these blends lost their advantageous mechanical properties upon exposure to water due to extraction of the polyether component [2]. Covalently crosslinked polymer networks are attractive for biomedical applications since it is possible to tailor their elastic properties and functions by adjusting their chemical composition and architecture [4], [5]. Polymer segments incorporated in such networks cannot be extracted due to their covalent crosslinking. Degradability of the material can be established by introducing hydrolizable bonds in the polymer segment or netpoints [6]. It was hypothesized, that by incorporating PECA into a polymer network with much lower Tg, the brittleness of the PECA material may be reduced. Oligoethylene glycol (OEG) might be suitable for usage as an additional component due to its biocompatibility and low protein absorption, which makes it one of the most widely explored polymers for biomedical applications [7]. At the same time, OEG based networks are highly hydrophilic. Thus they are prone to massive swelling in an aqueous environment. Combining them with a more hydrophobic polymer such as PECA may overcome this issue. When aimin
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