Effect of dangling chains on the structure and physical properties of a tightly crosslinked poly(ethylene glycol) network

Major imperfections in crosslinked polymers include loose or dangling chain ends that lower the crosslink d., thereby reducing elastic recovery and increasing the solvent swelling. These imperfections are hard to detect, quantify and control when the network is initiated by free radical reactions. As an alternative approach, the sol-​gel synthesis of a model poly(ethylene glycol) (PEG-​2000) network is described using controlled amts. of bis- and mono-​triethoxy silyl Pr urethane PEG precursors to give silsesquioxane (SSQ, R-​SiO1.5) structures as crosslink junctions with a controlled no. of dangling chains. The effect of the no. of dangling chains on the structure and connectivity of the dried SSQ networks has been detd. by step-​crystn. differential scanning calorimetry. The role that micelle formation plays in controlling the sol-​gel PEG network connectivity has been studied by dynamic light scattering of the bis- and mono-​triethoxy silyl precursors and the networks have been characterized by 29Si solid state NMR, sol fraction and swelling measurements. These show that the dangling chains will increase the mesh size and water uptake. Compared to other end-​linked PEG hydrogels, the SSQ-​crosslinked networks show a low sol fraction and high connectivity, which reduces solvent swelling, degree of crystallinity and the crystal transition temp. The increased degree of freedom in segment movement on the addn. of dangling chains in the SSQ-​crosslinked network facilitates the packing process in crystn. of the dry network and, in the hydrogel, helps to accommodate more water mols. before reaching equil.

Performance of R-N(R′)-R″ functionalised poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monolithic sorbent for plasmid DNA adsorption

High-throughput plasmid DNA (pDNA) manufacture is obstructed predominantly by the performance of conventional stationary phases. For this reason, the search for new materials for fast chromatographic separation of pDNA is ongoing. A poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (GMA-EGDMA) monolithic material was synthesised via a thermal-free radical reaction, functionalised with different amino groups from urea, 2-chloro-N,N-diethylethylamine hydrochloride (DEAE-Cl) and ammonia in order to investigate their plasmid adsorption capacities. Physical characterisation of the monolithic polymer showed a macroporous polymer having a unimodal pore size distribution pivoted at 600 nm. Chromatographic characterisation of the functionalised polymers using pUC19 plasmid isolated from E. coli DH5α-pUC19 showed a maximum plasmid adsorption capacity of 18.73 mg pDNA/mL with a dissociation constant (KD) of 0.11 mg/mL for GMA-EGDMA/DEAE-Cl polymer. Studies on ligand leaching and degradation demonstrated the stability of GMA-EGDMA/DEAE-Cl after the functionalised polymers were contacted with 1.0 M NaOH, which is a model reagent for most 'cleaning in place' (CIP) systems. However, it is the economic advantage of an adsorbent material that makes it so attractive for commercial purification purposes. Economic evaluation of the performance of the functionalised polymers on the grounds of polymer cost (PC)/mg pDNA retained endorsed the suitability of GMA-EGDMA/DEAE-Cl polymer.

Chemical toughening of epoxies. I. Structural modification of epoxy resins by reaction with hydroxy-terminated poly (butadiene-co-acrylonitrile)

In an attempt to toughen the epoxy resin matrix for fiber-reinforced composite applications, a chemical modification procedure of a commercially available bisphenol-A-based epoxy resin using reactive liquid rubber HTBN [hydroxy-terminated poly(butadiene-co-acrylonitrile)] and TDI (tolylene diisocyanate) is described. The progress of the reaction and the structural changes during modification process are studied using IR spectroscopy, viscosity data, and chemical analysis (epoxy value determination). The studies support the proposition that TDI acts as a coupling agent between the epoxy and HTBN, forming a urethane linkage with the former and an oxazolidone ring with the latter. The chemical reactions that possibly take place during the modification are discussed.

Chemical toughening of epoxies. I. Structural modification of epoxy resins by reaction with hydroxy-terminated poly(butadiene-co-acrylonitrile)

In an attempt to toughen the epoxy resin matrix for fiber-reinforced composite applications, a chemical modification procedure of a commercially available bisphenol-A-based epoxy resin using reactive liquid rubber HTBN [hydroxy-terminated poly(butadiene-co-acrylonitrile)] and TDI (tolylene diisocyanate) is described. The progress of the reaction and the structural changes during modification process are studied using IR spectroscopy, viscosity data, and chemical analysis (epoxy value determination). The studies support the proposition that TDI acts as a coupling agent between the epoxy and HTBN, forming a urethane linkage with the former and an oxazolidone ring with the latter. The chemical reactions that possibly take place during the modification are discussed.

Noves aproximacions a la síntesi i caracterització de poliglicols al·lílics, polihidrosiloxans i surfactants copolimèrics. Avaluació d'aquests surfactants en formulacions de poliuretà

Els polímers són una sèrie de compostos que troben un ampli ventall d'aplicacions en la indústria actual. Un exemple són les espumes de poliuretà, estructures de tipus cel·lular obtingudes mitjançant la reacció química entre compostos de tipus isocianat i compostos de tipus poliol (polièters amb diferent nombre de grups hidroxil). És imprescindible l'ús d'additius d'estructura tensioactiva (surfactants de silicona) per estabilitzar el procés d'espumació i per proporcionar una estructura cel·lular ordenada i homogènia en mida i distribució. La síntesis i caracterització de les molècules precursores (polihidrosiloxans i polièters al·lílics), l'estudi de la reacció d'hidrosililació com a via d'obtenció dels diferents surfactants per reacció d'addició entre els polihidrosiloxans i els polièters al·lílics i la caracterització i avaluació en formulacions comercials de poliuretà dels surfactants sintetitzats han constituït els objectius del present treball. MEMÒRIA La Tesi Doctoral ha estat presentada seguint el següent esquema: CAPÍTOL I. INTRODUCCIÓ A LA QUÍMICA DEL POLIURETÀ. Es presenten els principis de la química del poliuretà, fent esment dels recents avenços en la síntesis i caracterització d'aquests compostos polimèrics, així com un apartat concret centrat en els surfactants de silicona. Es presenten les estructures habituals d'aquests compostos comercials i es detallen les reaccions de síntesi i les característiques físiques que aquests compostos proporcionen a les espumes de poliuretà. CAPÍTOL II. OBJECTIUS. 1.- Síntesis y caracterització d'una àmplia gamma de poliglicols al·lílics i de polihidrosiloxans amb grups hidrur reactius, ambdós precursors d'estructures polimèriques de tipus surfactant. 2.- Estudi de la reacció d'hidrosililació com a via de formació d'enllaços Si-C no hidrolitzables, mitjançant la reacció d'addició entre els substrats al·lílics insaturats i els polisiloxans amb grups hidrur reactius. 3.- Caracterització de les estructures polimèriques de tipus surfactant sintetitzades i avaluació d'aquestes en formulacions de poliuretà, a fi de relacionar l'estructura química d'aquests oligómers amb els efectes físics que originen en l'espuma de poliuretà. CAPÍTOL III. SÍNTESI I CARACTERITZACIÓ DE SUBSTRATS AL·LÍLICS INSATURATS DE TIPUS POLIGLICOL. S'han caracteritzat per HPLC-UV una sèrie de polietilenglicols comercials. S'ha estudiat la reacció de derivatització al·lílica sobre els grups hidroxil dels polièters comercials (PEG, PPG i copolímers PEG-PPG) i s'han caracteritzat exhaustivament els productes sintetitzats (1H,13C-RMN, GC, GC-MS, FTIR, ESI-MS, HPLC-UV). S'ha iniciat un estudi de polimerització aniònica sobre nous epòxids amb un punt de diversitat molecular, sintetitzant-se i caracteritzant-se els corresponents nous polièters obtinguts. CAPÍTOL IV. SÍNTESI I CARACTERITZACIÓ DE POLIHIDROSILOXANS REACTIUS. S'estudia la síntesis de polihidrosiloxans amb grups hidrur reactius, mitjançant la reacció de polimerització aniònica d'obertura d'anell ("AROP, anionic ring opening polimerization") i mitjançant la reacció de polimerització per equilibració catiònica. Es presenta una caracterització exhaustiva dels productes sintetitzats i es descriu la naturalesa de la microestructura polimèrica a partir de la distribució bivariant dels copolímers PDMS-co-PHMS (poli(dimetilsiloxà)-co-poli(hidrometilsiloxà)). CAPÍTOL V. ESTUDI SISTEMÀTIC DE LA REACCIÓ D'HIDROSILILACIÓ. S'ha estudiat la reacció d'hidrosililació amb la finalitat de sintetitzar estructures copolimèriques poliglicol-polisiloxà a partir de la reacció de polisiloxans hidrur reactius i polièters al·lílics. S'han provat diferents catalitzadors (Pt/C 5%, cat. de Speier i cat. de Karstedt), s'han sintetitzat diferents estructures tensoactives (lineals i ramificades) i s'ha modelitzat les diferents reaccions secundàries observades, per presentar un estudi mecanístic de la reacció d'hidrosililació aplicada a la síntesis de molècules d'elevat PM a partir de la reacció entre substrats al·lílics insaturats i polihidrosiloxans. CAPÍTOL VI. AVALUACIÓ DELS SURFACTANTS EN FORMULACIONS DE POLIURETÀ. S'ha estudiat la idoneïtat dels surfactants de silicona sintetitzats en diferents formulacions de poliuretà comercials. S'ha relacionat el comportament físic d'aquests surfactants en les espumes de poliuretà amb la seva estructura química a partir de l'anàlisi per microscòpia electrònica de rastreig. CAPÍTOL VII. CONCLUSIONS. S'han esposat les conclusions extretes de cada capítol.

Urea amperometric biosensors based on a multifunctional bipolymeric layer: Comparing enzyme immobilization methods

This paper outlines the results obtained with biosensors designed for urea amperometric detection. The incorporation of urease into a bipolymeric substrate consisting of poly(pyrrole) and poly(5-amino-1-naphthol) was performed through four different approaches: direct adsorption, entrapment in cellulose acetate layer. cross-linking with glutaraldehyde, and also covalent attachment to the polymeric matrix. Poly(pyrrole) acts as amperometric transducer in these biosensors, while poly(5-amino-1-naphthol) drastically reduces the interference signal of agents such as ascorbic and uric acids. The biosensors containing urease covalently attached to the substrate provided interesting results in terms of sensitivity towards urea (0.50 mu A cm(-2) mmol(-1) L), lifetime (20 days) and short response times, due to the enzyme immobilization method used. All biosensors analyzed showed also a wide linear concentration range (up to 100 mmol L(-1)) and low detection limits (0.22-0.58 mmol L(-1)). (C) 2009 Elsevier B.V. All rights reserved.

Structural modelling of Eu3+-based siloxane-poly( oxyethylene) nanohybrids

The modelling of the local structure of sol-gel derived Eu3+-based organic/inorganic hybrids is reported, based on Small-Angle X-ray Scattering (SAXS), photoluminescence and mid-infrared spectroscopy. The hybrid matrix of these organically modified silicates, classed as di-ureasils and termed U(2000) and U(600), is formed by poly( oxyethylene) (POE) chains of variable length grafted to siloxane domains by means of urea cross-linkages. Europium triflate, Eu(CF3SO3)(3), was incorporated in the two di-ureasil matrices with compositions 400 greater than or equal ton greater than or equal to 10, n is the molar ratio of ether oxygens per Eu3+. The SAXS data for undoped hybrids (n=infinity) show the presence of a well-defined peak attributed to the existence of a liquid-like spatial correlation of siloxane rich domains embedded in the polymer matrix and located at the ends of the organic segments. The obtained siloxane particle gyration radius Rg(1) is around 5 Angstrom (error within 10%), whereas the interparticle distance d is 25 +/-2 Angstrom and 40 +/-2 Angstrom, for U(600) and U(2000), respectively. For the Eu3+-based nanocomposites the formation of a two-level hierarchical local structure is discerned. The primary level is constituted by strongly spatially correlated siloxane particles of gyration radius Rg(1) (4-6 and 3-8 Angstrom, errors within 5%, for U(600())n Eu(CF3SO3)(3), 200 greater than or equal ton greater than or equal to 40, and U(2000)(n)Eu(CF3SO3)(3), 400 greater than or equal ton greater than or equal to 40, respectively) forming large clusters of gyration radius Rg(2) (approximate to 75 +/- 10 Angstrom). The local coordination of Eu3+ in both di-ureasil series is described combining the SAXS, photoluminescence and mid-infrared results. In the di-ureasils containing long polymer chains, U(2000)(n)Eu(CF3SO3)(3), the cations interact exclusively with the carbonyl oxygens atoms of the urea bridges at the siloxane-POE interface. In the hybrids containing shorter chains, U(600)(n)Eu(CF3SO3)(3) with n ranging from 200 to 60, the Eu3+ ions interact solely with the ether-type oxygens of the polymer chains. Nevertheless, in this latter family of hybrids a distinct Eu3+ local site environment involving the urea cross-linkages is detected when the europium content is increased up to n=40.

Energy-transfer mechanisms and emission quantum yields in Eu3+-based siloxane-poly(oxyethylene) nanohybrids

We report the energy-transfer mechanisms and emission quantum yield measurements of sol-gel-derived Eu3+-based nanohybrids. The matrix of these materials, classified as diureasils and termed U(2000) and U(600), includes urea cross-links between a siliceous backbone and polyether-based segments of two molecular weights, 2000 and 600, respectively. These materials are full-color emitters in which the Eu3+ (5)Do --> F-7(0-4) lines merge with the broad green-blue emission of the nanoscopic matrix's backbone. The excitation spectra show the presence of a large broad band (similar to 27000-29000 cm(-1)) undoubtedly assigned to a ligand-to-metal charge-transfer state. Emission quantum yields range from 2% to 13.0% depending on the polymer molecular weight and Eu3+ concentration. Energy transfer between the hybrid hosts and the cations arises from two different and independent processes: the charge-transfer band and energy transfer from the hybrid's emitting centers. The activation of the latter mechanisms induces a decrease in the emission quantum yields (relative to undoped nanohybrids) and permits a fine-tuning of the emission chromaticity across the Comission Internacionalle d'Eclairage diagram, e.g., (x, y) color coordinates from (0.21, 0.24) to (0.39, 0.36). Moreover, that activation depends noticeably on the ion local coordination. For the diureasils with longer polymer chains, energy transfer occurs as the Eu3+ coordination involves the carbonyl-type oxygen atoms of the urea bridges, which are located near the hybrid's host emitting centers. on the contrary, in the U(600)-based diureasils, the Eu3+ ions are coordinated to the polymer chains, and therefore, the distance between the hybrid's emitting centers and the metal ions is large enough to allow efficient energy-transfer mechanisms.

Small-angle X-ray scattering study of gelation and aging of Eu3+-doped sol-gel-derived siloxane-poly(oxyethylene) nanocomposites

The aggregation, gelation, and aging of urea-cross-linked siloxane-poly(oxyethylene) nanohybrids [(U600)-n] containing two different amounts of europium triflate initially dissolved in an ethanol-water mixture were investigated by in situ small-angle X-ray scattering (SAXS). For both low (n = [O]/[Eu] = 80) and high (n = 25) europium contents, the SAXS intensity was attributed to the formation of siloxane clusters of about 8-11 Angstrom in size. Siloxane cluster formation and growth is a rapid process in hybrids with low Eu contents and slow in Eu-rich hybrids. An additional contribution to the scattering intensity at very low angles was attributed to the formation of a coarse structure level. At this secondary level, the structure can be described as a set of dense domains containing siloxane clusters embedded in a depleted matrix composed of unfolded polymer chains and solvent. By fitting a theoretical function for this model to the experimental SAXS curves, relevant structural parameters were determined as functions of time during the sol-gel transition and gel aging. For hybrids with low europium contents (n = 80), the size of the siloxane clusters remains essentially invariant, whereas the dense segregation domains progressively grow. In hybrids with high doping contents (n = 25), the preponderant structure variation during the first stages of the sol-gel transformation is the slow growth of siloxane clusters. For these hybrids, the segregation of siloxane clusters forming dense domains occurs only during advanced stages of the process.

Structure of magnetic poly(oxyethylene)-siloxane nanohybrids doped with Fe-II and Fe-III

Hybrid organic - inorganic nanocomposites doped with Fe-II and Fe-III ions and exhibiting interesting magnetic properties have been obtained by the sol - gel process. The hybrid matrix of these ormosils ( organically modified silicates), classed as di-ureasils and termed U( 2000), is composed of poly( oxyethylene) chains of variable length grafted to siloxane groups by means of urea crosslinkages. Iron perchlorate and iron nitrate were incorporated in the diureasil matrices, leading to compositions within the range 80 greater than or equal to n greater than or equal to 10, n being the molar ratio of ether-type O atoms per cation. The structure of the doped diureasils was investigated by small-angle X-ray scattering (SAXS). For Fe-II-doped samples, SAXS results suggest the existence of a two-level hierarchical structure. The primary level is composed of spatially correlated siloxane clusters embedded in the polymeric matrix and the secondary, coarser level consists of domains where the siloxane clusters are segregated. The structure of Fe-III-doped hybrids is different, revealing the existence of iron oxide based nanoclusters, identified as ferrihydrite by wide-angle X-ray diffraction, dispersed in the hybrid matrix. The magnetic susceptibility of these materials was determined by zero-field-cooling and field-cooling procedures as functions of both temperature and field. The different magnetic features between Fe-II- and Fe-III-doped samples are consistent with the structural differences revealed by SAXS. While Fe-II-doped composites exhibit a paramagnetic Curie-type behaviour, hybrids containing Fe-III ions show thermal and field irreversibilities.

Local structure and near-infrared emission features of neodymium-based amine functionalized organic/inorganic hybrids

Nd3+-based organic/inorganic hybrids have potential application in the field of integrated optics. Attractive sol-gel derived di-urea and di-urethane cross-linked poly (oxyethylene) (POE)/siloxane hybrids (di-ureasils and di-urethanesils, respectively) doped with neodymium triflate (Nd(CF3SO3)(3)) were examined by Fourier transform mid-infrared (FT-IR), Raman (FT-Raman), Si-29 magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and photoluminescence spectroscopies, and small-angle X-ray scattering (SAXS). The goals of this work were to determine which cation coordinating site of the host matrix (ether oxygen atoms or carbonyl oxygen atoms) is active in each of the materials analyzed, its influence on the nanostructure of the samples and its relation with the photoluminescence properties. The main conclusion derived from this study is that the hydrogen-bonded associations formed throughout the materials play a major role in the hybrids nanostructure and photoluminescence properties.

Magnetic sol-gel derived poly(oxyethylene)-siloxane nanohybrids

The magnetic and structural properties of sol-gel derived organic/inorganic nanocomposites doped with Fe(II), Fe(III), Nd(III) and Eu (III) ions are discussed. These hybrids consist of poly(oxyethylene)-based chains grafted onto siloxane nanodomains by urea cross-linkages. Small angle X-ray scattering data show the presence of spatial correlations of siloxane domains embedded in the polymer matrix. The magnetic properties of rare-earth doped samples are determined by single ion crystal-field-splitted levels (Eu3+ J=0; Nd3+ J=9/2) and the small thermal irreversibility is mainly associated to structural effects. Fe2+ -doped samples behave as simple paramagnet with residual antiferromagnetic interactions. Fe3+-doped hybrids are much more complex, with magnetic hysterisis, exchange anisotropy and thermal irreversibility at low temperatures. Néel temperatures increase up to 14K for the highest (∼5.5%) Fe3+ mass concentration.

Controlled swollen and drug release from urea-cross-linked polyether/siloxane hybrids

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nicht-wässrige Emulsionspolymerisationen

Die vorliegende Arbeit beschäftigt sich mit der Darstellung von Latexpartikeln in nicht-wässrigen Emulsionssystemen. Hintergrund der Untersuchungen war die Frage, ob es durch die Anwendung von nicht-wässrigen Emulsionen ermöglicht werden kann, sowohl wassersensitive Monomere als auch feuchtigkeitsempfindliche Polymerisationen zur Darstellung von Polymer-Latexpartikeln und deren Primärdispersionen einzusetzen. Das Basiskonzept der Arbeit bestand darin, nicht-wässrige Emulsionen auf der Basis zweier nicht mischbarer organischer Lösungsmittel unterschiedlicher Polarität auszubilden und anschließend die dispergierte Phase der Emulsion zur Synthese der Latexpartikel auszunutzen. Hierzu wurden verschiedene nicht-wässrige Emulsionssysteme erarbeitet, welche als dispergierte Phase ein polares und als kontinuierliche Phase ein unpolares Lösungsmittel enthielten. Auf Basis dieser Ergebnisse wurde in den nachfolgenden Untersuchungen zunächst die Anwendbarkeit solcher Emulsionen zur Darstellung verschiedener Acrylat- und Methacrylatpolymerdispersionen mittels radikalischer Polymerisation studiert. Um zu zeigen, dass die hier entwickelten nicht-wässrigen Emulsionen auch zur Durchführung von Stufenwachstumsreaktionen geeignet sind, wurden ebenfalls Polyester-, Polyamid- und Polyurethan-Latexpartikel dargestellt. Die Molekulargewichte der erhaltenen Polymere lagen bei bis zu 40 000 g/mol, im Vergleich zu wässrigen Emulsions- und Miniemulsions¬polymerisationssystemen sind diese um den Faktor fünf bis 30 höher. Es kann davon ausgegangen werden, dass hauptsächlich zwei Faktoren für die hohen Molekulargewichte verantwortlich sind: Zum einen die wasserfreien Bedingungen, welche die Hydrolyse der reaktiven Gruppen verhindern, und zum anderen die teilweise erfüllten Schotten-Baumann-Bedingungen, welche an der Grenzfläche zwischen dispergierter und kontinuierlicher Phase eine durch Diffusion kontrollierte ausgeglichene Stöchiometrie der Reaktionspartner gewährleisten. Somit ist es erstmals möglich, hochmolekulare Polyester, -amide und -urethane in nur einem Syntheseschritt als Primär¬dispersion darzustellen. Die Variabilität der nicht-wässrigen Emulsionen wurde zudem in weiteren Beispielen durch die Synthese von verschiedenen elektrisch leitfähigen Latices, wie z.B. Polyacetylen-Latexpartikeln, aufgezeigt. In dieser Arbeit konnte gezeigt werden, dass die entwickelten nicht-wässrigen Emulsionen eine äußerst breite Anwendbarkeit zur Darstellung von Polymer-Latexpartikeln aufweisen. Durch die wasserfreien Bedingungen erlauben die beschriebenen Emulsionsprozesse, Latexpartikel und entsprechende nicht-wässrige Dispersionen nicht nur traditionell radikalisch, sondern auch mittels weiterer Polymerisationsmechanismen (katalytisch, oxidativ oder mittels Polykondensation bzw. -addition) darzustellen.

Long-term in vivo biostability of poly(dimethylsiloxane) / poly(hexamethylene oxide) mixed macrodiol-based polyurethane elastomers

The long-term biostability of a novel thermoplastic polyurethane elastomer (Elast-Eon(TM) 2 80A) synthesized using poly(hexamethylene oxide) (PHMO) and poly(dimethylsiloxane) (PDMS) macrodiols has been studied using an in vivo ovine model. The material's biostability was compared with that of three commercially available control materials, Pellethane(R) 2363-80A, Pellethane(R) 2363-55D and Bionate(R) 55D, after subcutaneous implantation of strained compression moulded flat sheet dumbbells in sheep for periods ranging from 3 to 24 months. Scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to assess changes in the surface chemical structure and morphology of the materials. Gel permeation chromatography, differential scanning calorimetry and tensile testing were used to examine changes in bulk characteristics of the materials. The results showed that the biostability of the soft flexible PDMS-based test polyurethane was significantly better than the control material of similar softness, Pellethane(R) 80A, and as good as or better than both of the harder commercially available negative control polyurethanes. Pellethane(R) 55D and Bionate(R) 55D. Changes observed in the surface of the Pellethane(R) materials were consistent with oxidation of the aliphatic polyether soft segment and hydrolysis of the urethane bonds joining hard to soft segment with degradation in Pellethane(R) 80A significantly more severe than that observed in Pellethane(R) 55D. Very minor changes were seen on the surfaces of the Elast-Eon(TM) 2 80A and Bionate(R) 55D materials. There was a general trend of molecular weight decreasing with time across all polymers and the molecular weights of all materials decreased at a similar relative rate. The polydispersity ratio, M-w/M-n, increased with time for all materials. Tensile tests indicated that UTS increased in Elast-Eon(TM) 2 80A and Bionate(R) 55D following implantation under strained conditions. However, ultimate strain decreased and elastic modulus increased in the explanted specimens of all three materials when compared with their unimplanted unstrained counterparts. The results indicate that a soft, flexible PDMS-based polyurethane synthesized using 20% PHMO and 80% PDMS macrodiols has excellent long-term biostability compared with commercially available polyurethanes. (C) 2004 Elsevier Ltd. All rights reserved.