The outstanding hydrolytic and oxidative stabilities of polyisobutylene-based polyurethanes (PIB-based PUs) were reported earlier. Herein, we summarize recent investigations aimed at further enhancing hydrolytic-oxidative stabilities (in terms of resistance to aqueous buffer, nitric acid and CoCl2/H2O2) together with excellent mechanical properties. The purity and dryness of ingredients together with precise NCO/OH stoichiometry (∼1.05) are essential to obtain PIB-based PUs with improved properties. Static and dynamic mechanical properties were optimized by analyzing stress–strain traces, thermal (TGA, DSC) responses, self-organization (XRD) profiles, and rheological (DMA, creep) information. According to microstructure and surface analyses (AFM, contact angle) annealing increases the segregation of individual segments and increases surface hydrophobicity, which in turn enhances the shielding of hydrolytically oxidatively vulnerable carbamate bonds by inert PIB barriers, and thus significantly improves hydrolytic-oxidative stability. Annealing does not much affect bulk properties, such as static and dynamic mechanical and thermal properties; however, it increases damping over a wide temperature range. Annealed PIB-based PU containing 72.5% PIB exhibits outstanding hydrolytic-oxidative stability together with ∼26 MPa tensile strength, ∼500% elongation, and ∼77 Microshore hardness. PIB-based PUs are significantly more resistant to hydrolytic and oxidative degradation than ElastEon™ E2A, a commercially available PDMS-based PU, widely used for medical applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 532–543
We extended our investigations of rubbery wound closure adhesives and created novel flexible networks by crosslinking cyanoacrylated silicone rubbers (i.e., commercial methylhydrosiloxane-dimethylsiloxane copolymers, PMHS-co-PDMS) with N,N-dimethyl-p-toluidine in tetrahydrofuran and hexamethyldisiloxane solvents at room temperature. Cyanoacrylation was achieved by hydrosilating (anthracene-protected) allyl cyanoacrylate with PMHS-co-PDMS. Steric hindrance and the molecular weight of the copolymer strongly affect the extent of hydrosilation. The rate of crosslinking is proportional with the number of cyanoacrylate groups in the copolymer and networks form in seconds with appropriate amounts of initiator. Networks on porcine skin yield well-adhering flexible optically-transparent colorless conformal coatings of good “feel” appropriate for clinically useful non-occlusive “breathable” skin or wound protectors. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1367-1372
Polyisobutylene (PIB)-based polyurethanes (PUs) exhibit unparalleled hydrolytic-oxidative-biologic stability and are melt processible, however, their mechanical (strength) properties are modest mainly due to insufficient H bonds. We posited and demonstrate that the ultimate properties of PIB-PUs are enhanced, while their melt processibility is maintained, by the judicious introduction of urea linkages, i.e., strong bifurcated H bonds, in the chain. The incorporation of bifurcated H bonds in PIB-PUs was achieved by using the conventional butane diol chain extender (CE) in combination with controlled amounts of amino alcohol as co-chain extender (co-CE). Polyurethanes containing both urethane and urea linkages are polyurethane-ureas (PUU). Specifically, PIB-PUUs prepared with PIB-diol/MDI together with 80/20 mole % butane diol/amino butanol exhibited ∼30 MPa tensile strength, ∼550% elongation, ∼80 Shore A hardness, and ∼137 °C flow temperature. Other amino alcohols, i.e., amino ethanol, -propanol, and -hexanol, were less effective co-CEs. 1H-NMR and FT-IR spectroscopies indicate the presence of bifurcated H bonds in PIB-PUUs prepared with CE/co-CE combinations. Characterization by differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical thermal analysis, and creep experiments also suggest bifurcated H bonds in PIB-PUU. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2361–2369
The polymerization of 2-octyl cyanoacrylate (OctCA) initiated by five N-bases [N,N-dimethyl-p-toluidine (DMT), pyridine (Pyr), triethyl amine (Et3N), azobicyclo[2.2.2]octane (ABCO), and diazobicylo[2.2.2]octane (DABCO)] was investigated. Our main objective was to assess the suitability and relative reactivity of these initiators for neat OctCA polymerization as wound closure adhesives. Methodologies were developed to determine stir-stop and set times of OctCA polymerization and to use these quantities to assess initiation reactivity. According to these studies Et3N, ABCO, DABCO, and Pyr are most reactive initiators, while DMT is much less reactive. Polymerizations were much faster in the presence of small amounts of tetrahydrofuran than toluene, indicating solvent polarity effects. Initiator reactivity is discussed in terms of structural parameters. NMR and MALDI-TOF analyses of low molecular weight P(OctCA) prepared with DMT did not show evidence for the expected aromatic head group proposed by earlier investigators, which suggests complex initiation mechanism. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1652–1659
Novel rubbery wound closures containing various proportions and molecular weights of polyisobutylene (PIB) and poly(2-octyl cyanoacrylate) [P(OctCA)] for potential clinical use were designed, synthesized, characterized, and tested. Homo-networks were prepared by crosslinking 3-arm star-shaped PIBs fitted with terminal cyanoacrylate groups, [Ø(PIB-CA)3], and co-networks by copolymerizing Ø(PIB-CA)3 with OctCA using N-dimethyl-p-toluidine (DMT). Neat Ø(PIB-CA)3, and Ø(PIB-CA)3/OctCA blends, upon contact with initiator, polymerize within seconds to optically transparent strong rubbery co-networks, Ø(PIB-CA)3-co-P(OctCA). Homo- and co-network formation was demonstrated by sol/gel studies, and structures and properties were characterized by a battery of techniques. The Tg of P(OctCA) is 58 °C by DSC, and 75 °C by DMTA. Co-networks comprising 25% Ø(PIB-CA)3 (Mn = 2400 g/mol) and 75% P(OctCA) are stronger and more extensible than skin. Short and long term creep studies show co-networks exhibit high dimensional stability and <6% creep strain at high loading. When deposited on porcine skin co-networks yield hermetically-adhering clear rubbery coatings. Strips of porcine skin coated with co-networks could be stretched and twisted without compromising membrane integrity. The co-network is nontoxic to L-929 mouse fibroblasts. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1640–1651
We discovered that polyisobutylene (PIB)-based polyurethanes (PIB-PUs) containing minute amounts (0.5%) of chemically bound organically modified montmorillonite (OmMMT) surprisingly produce films exhibiting improved properties. The OmMMT was prepared by reacting sodium montmorillonite (Na+MMT−) with quaternary ammonium salts of a tertiary amine carrying a NH2 functionality. The positively charged quaternary amine group becomes electrostatically attached to negatively charged MMT layers and defoliates it, whereas the free NH2 group reacts with diisocyanates and acts as an additional chain extender. Thus, when OmMMT is added to a mixture of ingredients assembled for the synthesis of PIB-PUs, this modified clay becomes an integral part of the PU. Specifically, we found that the integration of 0.5% OmMMT to PIB-based PUs produces films with significantly enhanced tensile strength, elongation, toughness, creep, and stress relaxation relative to that of PIB-PUs. The findings were discussed and explained in terms of a proposed morphology for the nanocomposite. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4076–4087
This highlight concerns the birth, development, and present status of unique polyurethanes consisting of polyisobutylene soft segments and conventional hard segments (PIB-based PUs) exhibiting unprecedented combinations of mechanical properties and oxidative/hydrolytic/biological stability. Impetus for developments was to improve the rather poor chemical resistance of conventional polyurethanes by replacing their soft segments with polyisobutylene segments. Research started in the 1980s with the synthesis of α,ω-polyisobutylene diols (HO-PIB-OH) by the inifer technique and preparation of PIB-based PUs, which indeed exhibited outstanding stabilities, however, had poor mechanical properties. Because of cumbersome early techniques and expensive reagents, worldwide research and industrial interest waned and developments went into hibernation. Recent discoveries, including living isobutylene polymerization, improved end-functionalizations, inexpensive ingredients, and new insight into PU morphology, lead to simple and less expensive synthesis strategies and, consequently, to resumption of fundamental and applied research. Presently, we can produce kilogram quantities of polyurethanes and polyureas with unprecedented combinations of excellent physical–mechanical–environmental–biological and processing properties. This highlight focuses on facts and insights, which occurred since the discovery and shaped developments. These events are worth reviewing and analyzing because they illustrate how contemporary academic research is driven by curiosity (fun) and economic considerations (money). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Because of the presence of extensive H-bonding in the hard segments, polyureas are processed by solution techniques (e.g., dry spinning) by the use of relatively costly and environmentally unfriendly solvents. Thus, the objective of this research was to render polyureas melt processible, (i.e., to reduce their flow temperature, Tflow) without compromising their excellent mechanical properties. We hypothesized and herein demonstrate that by using conventional chain extenders (CEs) in combination with small amounts of H-bond acceptor chain extenders (HACEs), the Tflow of polyureas can be significantly reduced from ∼230 to ∼180 °C, and thus melt processible products with excellent mechanical properties can be obtained. We document the synthesis of conventional polytetramethylene oxide-based and novel polyisobutylene (PIB)-based polyureas with Tflows ∼ 180 °C and excellent mechanicals by the addition of few percents of commercially available HACEs. Products were characterized by various techniques, including Instron (tensile strengths, elongations), durometer (Shore A Hardness), dynamic mechanical thermal analysis (Tflow), and thermal gravimetric analysis (TGA) (thermal weight loss). According to TGA, a polyurea with Tflow of ∼180 °C did not degrade up to ∼234 °C in air. A micromorphology for melt processible polyureas is proposed that emphasizes flexibilized hard segments in the presence of HACEs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
The oxidative/hydrolytic stability of polyurethanes (PUs) containing exclusively polyisobutylene (PIB), or mixed PIB/polytetramethylene oxide (PTMO), or mixed PIB/polyhexamethylene carbonate (PC) soft segments was investigated. The tensile strengths and elongations of various PUs were determined before and after agitating in 35% HNO3 or 20% H2O2/0.1 M CoCl2 solutions and retentions were quantified. The presence of PIB imparts significant oxidative/hydrolytic resistance. The tensile strength and elongation of PUs containing 70% PIB, or those of mixed PIB/PC soft segments with 50% PIB, remained essentially unchanged upon exposure to HNO3; in contrast, PUs containing mixed PIB/PTMO soft segments with 50% PIB underwent significant degradation. The tensile strength of PUs with mixed PIB/PC (60/10%) soft segment increased after exposure to HNO3, most likely because of oxidative crosslinking of PC segments. PIB/PTMO- and PIB/PC-based PUs and commercially available PUs (Elast-Eon® and Carbothane®) were exposed to H2O2/CoCl2 solutions for up to 14 weeks. Although the experimental PIB/PC-based PUs exhibited negligible change in mechanical properties and no surface damage, Elast-Eon® and Carbothane® showed significant surface damage. PIB-based polyureas and Bionate® were implanted in rats for 4 weeks in vivo, and their biocompatibility was investigated. The biocompatibility of PIB-based materials was superior to Bionate®. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2194–2203, 2010
We describe the design, synthesis, characterization, and testing of novel polyurethanes (PUs) exhibiting unprecedented combinations of outstanding mechanical properties and oxidative/hydrolytic stabilities. This achievement is due to the use of polyisobutylene (PIB) soft segments plus flexible H-bond acceptor chain extenders (HACEs): the PIB imparts superior oxidative/hydrolytic stability and the HACE produces reinforcing H-bonds, which lead to outstanding mechanicals. Oxidative/hydrolytic stability was quantitated by retention of tensile strength and elongation after exposure to nitric acid. PUs containing 60–70% PIB retain their mechanical properties, whereas Carbothane®, Bionate®, and Elast-Eon™, PUs marketed for chemical stability, degrade severely under the same conditions. Various HACEs were identified (e.g., hexaethylene glycol, tripropylene glycol, tributylene glycol, 3,3′-diamino-N-methyl-dipropylamine, etc.) and their effect on mechanical properties was investigated. A PIB- and HACE-containing PU exhibited 29.2 MPa tensile strength, 620% elongation, and 80 Shore A hardness. Properties were analyzed in terms of stress–strain profiles, differential scanning calorimetry traces, dynamic mechanical thermal analysis plots, and oxidative/hydrolytic stability. The properties of various PIB-based rubbers, that is, thermoplastic PUs, SIBSTAR®, and thermoset butyl rubber are compared. The novel PUs are promising candidates for biomaterials and industrial applications where a combination of mechanical properties and oxidative/hydrolytic stability is of the essence. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2361–2371, 2010
Novel polyurethanes consisting of polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) or PIB/poly(hexamethylene carbonate) (PC) soft co-segments in combination with 4,4′-methylene-bis(cyclohexyl isocyanate)/1,6-hexanediol, 1,4-butanediol, or 1,6-hexamethylene diamine hard segments exhibit excellent mechanical properties (upto 31 MPa tensile strength with 700% elongation) together with unprecedented oxidative/hydrolytic stability. A structural model of the morphology of these polyurethanes was developed that reflects this combination of properties. The key new elements of our model are H bridges between the PTMO and PC type soft and urethane hard segments, which compatibilize the soft and hard domains, and the presence of large quantities of chemically resistant PIB soft segments that protect the other oxidatively/hydrolytically vulnerable constituents. A variety of FTIR, DSC, SAXS, AFM, and DMTA experiments strongly support the proposed morphological model. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6180–6190, 2009
The synthesis, characterization, and structure–property behavior of polyurethanes containing polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) soft co-segments and bis(4-isocyanatocyclohexyl)methane (HMDI)/hexanediol (HDO) hard segments is presented. The mechanical (stress/strain, hardness, and hysteresis) properties of these novel polyurethanes were investigated over a broad composition range. PIB-based polyurethanes with HMDI/HDO hard segments showed better mechanical properties than earlier polyurethanes containing highly crystalline hard segments. The addition of moderate amounts (20% by weight) of PTMO significantly increased both tensile strengths and elongation. In the presence of larger amounts of PIB, these polyurethanes are expected to possess oxidative/hydrolytic/enzymatic stabilities superior to commercially available polyurethanes. These polyurethanes are softer and exhibit hysteresis superior to or comparable with conventional polyurethanes. According to initial thermal studies, these materials show good melt processibility. Overall, the mechanical properties of PIB based hybrid polyurethanes are similar to commercially important polyurethane type biomaterials. Our results show that the incorporation of PTMO segments to PIB-based polyurethanes significantly improves elastomeric properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5278–5290, 2009
The design, synthesis, characterization, and structure–property behavior of polyureas containing novel soft segments of mixed polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) chains and conventional hard segments is presented. Modest amounts (12%) of PTMO in the soft PIB phase significantly increase both the tensile strength and elongation of the polyureas. These polyureas exhibit not only oxidative/hydrolytic stabilities far superior to Bionate® and Elast-Eon® considered the most oxidatively stable polyurethanes on the market but also display mechanical properties (29 MPa tensile strength and 200% elongation) approaching those of conventional thermoplastic polyurethanes. The surfaces of these polyureas are covered/protected by PIB segments, which will lead to excellent biocompatibility. Our results demonstrate that the PTMO segments facilitate stress transfer from the continuous mixed soft phase to the dispersed hard phase, which strengthens and flexibilizes PIB-based polyureas and thus significantly improves elastomeric properties without compromising oxidative and hydrolytic stability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2787–2797, 2009
Our main objective was the design, synthesis, characterization, and testing of a novel class of materials, thermoplastic amphiphilic conetworks (TP-APCNs). A further objective was the evaluation of TP-APCNs as biomaterials, for example, as immunoisolatory membranes in a bioartificial pancreas, or as extended-wear soft contact lenses. The synthesis of the first TP-APCNs was accomplished by blending an amphiphilic graft polymer, poly(dimethyl acryl amide)-g-polydimethylsiloxane (PDMAAm-g-PDMS), with a commercial PDMS-containing polyurethane (PU). The common PDMS segments coalesce and form a single phase, whereas the hard/crystalline segments of the PU physically crosslink the blend. The properties of TP-APCNs can be controlled by the graft/PU ratio and segment molecular weights. TP-APCNs with cocontinuous hydrophilic and hydrophobic phases were prepared as demonstrated by swelling in water and n-heptane. Depending on the blend ratio and molecular weights, optically clear water-swollen TP-APCNs with 0.5–4 MPa tensile strength, 70–280% elongation, together with 2–11 × 10−7 cm2/s glucose permeability, and 1.2–8 × 10−8 cm2/s insulin permeability were prepared. TP-APCNs are processible by casting and molding. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 682–691, 2009
Novel segmented polyurea elastomers containing soft polyisobutylene (PIB) segments were synthesized and characterized. The key ingredient, primary amine-telechelic PIB oligomers (NH2-PIB-NH2) with number average molecular weights of 2500 and 6200 g/mol were synthesized. PIB-based polyureas were prepared by using various aliphatic diisocyanates and diamine chain extenders with hard segment contents between 9.5 and 46.5% by weight. All copolymers displayed microphase morphologies as determined by dynamic mechanical analysis. Tensile strengths of nonchain-extended and chain-extended polyureas showed a linear dependence on the urea hard segment content. PIB-based polyureas prepared with NH2-PIB-NH2 of Mn = 2500 g/mol, 4,4′-methylendbis(cyclohexylisocyantate), and 1,6-diaminohexane containing 45% hard segment exhibited 19.5 MPa tensile strength which rose to 23 MPa upon annealing at 150 °C for 12 h. With increasing hard segment content, elongation at break decreased from ∼ 450% to a plateau of 110%. The hydrolytic and oxidative stability of PIB-based polyureas were unprecedented. Although commercial “oxidatively resistant” thermoplastic polyurethanes degraded severely upon exposure to boiling water or concentrated nitric acid, the experimental polyureas survived without much degradation in properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 38–48, 2009
Novel networks and conetworks were prepared by the instantaneous polymerization of cyanoacrylate-telechelic three-arm star polyisobutylene [Ø(PIB-CA)3] and the copolymerization of Ø(PIB-CA)3/2,4,4-trimethylpentane cyanoacrylate (TMP-CA) mixtures, respectively, by means of strong nucleophiles, such as NEt2-telechleic linear or three-arm star PIBs [Ø(PIB-NEt2)2 or 3]. The reactants were combined in the bulk in double-barrel syringes by reaction injection molding (RIM). The chemical and mechanical properties of products prepared in the bulk and by conventional solution techniques were characterized by various techniques (swelling, extractables, FTIR and NMR spectroscopies, Instron, microhardness, oxidative resistance, DSC, DMTA). Conditions for the preparation of rubbery materials for possible biomedical applications were developed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2612–2623, 2008
This series of papers concern new materials for possible biological applications created by combining the chemistry of highly reactive cyanoacrylates (CAs) with polyisobutylene (PIB) rubbers. First, a new strategy for the synthesis of CA–telechelic PIBs is described. Subsequently, the strategy is employed for the synthesis of low viscosity (syringible) CA–telechelic three-arm star PIB [Ø(PIB–CA)3]. The intermediates of the synthesis route are characterized by 1H NMR spectroscopy. Injecting liquid Ø(PIB–CA)3 into living tissue (fresh chicken egg) produces a bolus of crosslinked PIB rubber. The spectacular oxidative resistance of this rubber is documented by its resistance to concentrated HNO3. A structural model of the crosslinked rubber obtained upon contacting Ø(PIB–CA)3 with proteinaceous tissue is proposed. Copyright © 2007 John Wiley & Sons, Ltd.
This research concerned the synthesis and characterization of novel conetworks containing polyisobutylene (PIB) and polyethyl-2-cyanoacrylate [poly(Et-CA)] sequences. The syntheses involved the copolymerization of CA-telechelic three-arm star PIB [Ø(PIB-CA)3] with ethyl-2-cyanoacrylate (Et-CA) mediated by nucleophiles or by living tissue (fresh eggs). The conetworks were characterized by swelling in hexanes, tetrahydrofuran (THF), and acetone, and the results indicate co-continuous PIB and poly(Et-CA) domains. The conetworks exhibit two Tgs indicating phase-separation between PIB and poly(Et-CA). The outstanding oxidative resistance of the conetworks was demonstrated by exposure to concentrated nitric acid. The tensile strengths, moduli, and elongations of a series of conetworks with different overall compositions were investigated and the findings interpreted in terms of covalently linked rubbery and glassy domains. AFM also suggests the presence of phase-separated rubbery and glassy domains. DMTA spectra of a Ø(PIB-CA)3 homonetwork, and Ø(PIB-CA)3/Et-CA conetworks were analyzed and interpreted in terms of coexisting rubbery and glassy domains. Observations made during the exposure of Ø(PIB-CA)3/Et-CA mixtures to proteinaceous tissue, in combination with characterization data, were used to propose a structural model for the conetworks. Copyright © 2007 John Wiley & Sons, Ltd.
The objective of this research was to develop new strategies for the synthesis of novel optically clear highly oxygen permeable membranes exhibiting appropriate water uptake and mechanical properties for possible ophthalmic applications. Thus a series of bicontinuous amphiphilic conetworks containing well-defined poly- (ethylene glycol) and polydimethylsiloxane segments crosslinked by three novel crosslinking/modifying agents were synthesized, characterized, and evaluated. This paper concerns the design and synthesis of the crosslinking/modifying agents (see Fig. 2), and their use for the synthesis of clear, highly oxygen permeable amphiphilic membranes. Select membranes exhibit outstanding oxygen permeabilities (>200 barrers) far superior to contemporary commercial soft contact lenses, together with mechanical properties and water uptake appropriate for extended wear soft contact lens application. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 308–316, 2007
While two of our earlier papers on poly(dimethyl acryl amide)/polymethylhydrosiloxane/polydimethylsiloxane (PDMAAm/PMHS/PDMS) amphiphilic conetworks concerned synthesis and biological properties, respectively, the present contribution focuses on oxygen and insulin permeabilities, and select mechanical properties. We show that by increasing the PDMAAm content from 20 to 60% (i.e., by decreasing the hydrophobic content from 80 to 40%), oxygen permeabilities decrease from ∼240 to ∼130 barrers. Evidently, oxygen permeability is a function of the sum of the oxyphilic components, PDMS + PMHS, in the conetworks. In contrast, insulin permeability is a function of the hydrophilic component, and reaches a desirable 1.5 × 10−7 cm2/s at 61% PDMAAm. We also studied the permeabilities of glucose, dextran, and albumin through a PDMAAm61/PMHS6/PDMS33 membrane and found, unsurprisingly, that the permeability of these molecules follows their hydrodynamic radii, and we project that the permeability of IgG is infinitesimally low. Tensile strengths and ultimate elongations of water-swollen membranes are also a function of conetwork composition: by increasing the PDMAAm content from 30 to 60%, strengths decrease from 1.6 to 1.2 MPa, and elongations from ∼60 to ∼40%. Overall, the permeabilities and the mechanical properties of these membranes are appropriate for implantation and, specifically, for immunoisolation of living tissue. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4276–4283, 2007
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![1,2,3,4,5-CYCLOPENTANEPENTAYL, COMPD. WITH 1-[(1S)-1-(DIBICYCLO[2.2.1]HEPT-2-YLPHOSPHINO)ETHYL]-2-[2-(DIPHENYLPHOSPHINO)PHENYL]-1,2,3,4,5-CYCLOPENTANEPENTAYL, IRON SALT (1:1:1)](http://img.cochemist.com/ccimg/134000/133978-15-1_b.png)
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![Poly[imino(1-oxo-1,3-propanediyl)]](http://img.cochemist.com/ccimg/25000/24937-14-2_b.png)
