Segmented Poly Urethane-urea Research Articles

Stress-strain behavior of segmented polyurethaneureas under pure shear deformation

Elastic properties of segmented polyurethaneureas (SPUs) under pure shear deformation were investigated. Data were analyzed by using strain energy density function (W). The values of the derivatives of W with respect to the invariants of the strain tensor (I i ; i = 1, 2, 3 ) at zero strain limit were also estimated theoretically and were compared with those estimated by experiment. The limiting value of the derivative with respect to I 1 (∂W/∂I 1) was shown theoretically to be 5 G/8, while the derivatives with respect to I 2 and I 3 (∂W/∂I 2 and ∂W/∂I 3 were respectively-G/8 and -3G/8. The theoretical prediction could explain the asymptotic behavior of the derivatives of SPUs as well as isoprene rubber (IR) reported by Kawabata et al. at small I 1 limit.

1001-29 Prevention of Subacute Stent Thrombosis by Polymer-Polyethylene Oxide-Heparin Coating in the Rabbit Carotid Artery

Our goals were to develop a rabbit model of subacute stent thrombosis and to evaluate the efficacy of a polymer stent coating with covalently bound heparin for its prevention. Bare metal stents (a nitinol wire coil with 3 stainless steel joints) were implanted in a carotid artery of 10 NZW rabbits with a 3.0 mm balloon catheter, inflated twice at 6 atm for 1 minute. Systemic antiplatelet and antithrombotic therapy was withheld. Animals were sacrificed at 24, 72 and 96 hours. Only the 96 hour group consistently developed occlusive or subocclusive thrombosis. Heparin (0.28 μ g/cm 2 ) was linked onto the surface of soluble polymer chains of segmented polyurethaneurea (SPUU) or aliphatic Tecoflex polyurethane membrane (50 μ m thick). using polyethylene oxide (PEO) as a hydrophilic spacer group. Eight stents were coated with this polymer-PEO-Heparin coating. Eight bare metal stents and 8 coated stents were deployed in a carotid artery of 16 NZW rabbits. All animals were sacrificed at 96 hours. At the time of sacrifice, both carotids (stented and contralateral nonstented) were exposed and resting blood flow measured. The amount of thrombus on each stent was assessed by a semiquantitative grading scale (I: no lumen encroachment; II: lumen encroachment; III: subocclusive thrombus; IV: occlusive thrombus) and by the weight of the dry thrombus. Carotid Flow (ml/min) Thrombus Grade (III/IV) Thrombus Weight (mg) Bare Stent (N = 8) 3.8 ± 8.2 7 of 8 42.2 ± 19.9 Heparin Stent (N = 8) 210 ± 92 0 of 8 6.0 ± 2.4 p -value 0.0014 0.0004 0.00016 The 96 hour rabbit carotid model yields a high frequency of occlusive and subocclusive subacute thrombosis. The stents coated with polymer-PEO-Heparin accumulate significantly less thrombus and have better patency than the uncoated stents at 96 hours in this model of subacute stent thrombosis.

A criterion for microphase separation in segmented polyurethane and polyurethane ureas

A criterion for microphase separation in segmented polyurethanes and poly(urethane urea)s is proposed. The existence of correlation between the ratios χ hs (χ hs ) cr and the degree of segregation ( α seg) was established, where χ hs is the thermodynamic interaction parameter between soft and hard blocks, calculated from the solubility parameters, and ( χ hs) cr is its critical value, calculated using the Scott equation. Correlation between the ratio χ hs (χ hs ) cr , the degree of segregation α seg and the flexibility parameter σ was also found.

A Model Reaction for the Chain Extension Reaction of Polyurethaneurea: Rate of the Reaction between Butylamines and Phenyl Isocyanate

The reaction between butylamines and phenyl isocyanate was studied as a model reaction for the formation of the hard segment in segmented polyurethaneurea. Since the reaction was too fast to measure by a conventional titration method, aniline was used as a competitive component in the reaction between n-butylamine (NBA) or sec-butylamine (SBA) and phenyl isocyanate (PHI) at O, 17 and 39°C. The rate constants of the reaction be-tween NBA and PHI were 30.9×10-2, 44.2×10-2 and 59.3×10-2 L•mol-1 • s-1 at 0, 17 and 39°C and those for SBA and PHI were 8.3×10-2, 18.8×10-2 and 44.5×10-2 L•mol-1•s-1 at 0, 17 and 39°C, respectively, The activation energies were 2.8 and 7.3 kcal/mol, respectively.

An Annular Compliance Chamber for the Pennsylvania State University Electric Total Artificial Heart

To eliminate the need for a separate parapleural compliance chamber, we are currently investigating the feasibility of an annular compliance chamber. This chamber wraps around the energy converter and fits between the blood pumps of the Pennsylvania State University electric total artificial heart. For the 100 cc total artificial heart, the compliance chamber volume is 76 ml and the tissue contacting surface area is approximately 85 cm2. The chamber is made of Dacron velour covered segmented polyether polyurethane urea. The annular compliance chamber was evaluated in vitro by comparing pump balance control performance against that obtained with an open vent. In the CVP range of 5-12 mmHg, LAP was maintained within 1 mmHg of the values obtained with a vent. Studies continue to determine the range of volumes over which the chamber is effective, differences in rates of diffusion, and performance during changes in barometric pressure.

Morphology‐property relationship of segmented polyurethaneurea: Influences of soft‐segment structure and molecular weight

AbstractThe relationships of the morphology and properties of a series of segmented polyurethaneurea (PUU) were studied in film form by using SEM and tensile stress‐strain data. The polyether‐based and polyester‐based PUU block copolymers were synthesized using poly(propylene oxide) ‐ethylene oxide polyether or poly(butylene adipate) polyester with different molecular weights, 4,4‐methylene bis(phenyl isocyanate), and diethyltoluene diamine. The extent of phase separation increased with increasing molecular weight of the soft segment. The polyether‐based PUU showed better phase separation than did polyesterbased PUU with the same molecular weight soft segment. The polyether‐ester‐based PUU showed the morphology of both polyether‐based and polyester‐based PUU but with larger domain size and interface. © 1993 John Wiley & Sons, Inc.

Sorption of water vapor by hydrophilic polyurethane‐ureas

AbstractSegmented polyurethane‐ureas were prepared from low‐molecular weight homopolymers or triblock (PEP) copolymers of ethylene and propylene oxides and 4,4′‐diphenylmethane diisocyanate with hydrazine as chain extender. Equilibrium sorption of water vapor at 23°C was measured at eight to nine values of relative vapor pressure, 0.08 ≤ p/p0 ≤ 0.97. The effect of the structure (composition and length) of soft segments was studied. Sorption capacities were found to be lower than the reference values computed under the assumption that the contributions to sorption by the chain constituents are additive. This finding was assigned to the shielding effect of hard segment domains on the interaction of water molecules with hydrophilic (ethoxamer) groups of soft segments. © 1993 John Wiley & Sons, Inc.

Determination of Aromatic Amine in Segmented Polyurethaneurea.

Determination of Aromatic Amine in Segmented Polyurethaneurea.

Pervaporation of ethanol/water mixtures using novel hydrophobic membranes containing polydimethylsiloxane

Novel hydrophobic membranes made of crosslinked polydimethylsiloxane (PDMS), segmented polyurethaneurea containing PDMS as the soft segment and PDMS/polystyrene graft copolymer were prepared and pervaporation experiments were carried out with ethanol/water mixtures. It was found that ethanol permselectivity (separation factor of ethanol) increased with an increase in the crosslink distance, with soft segment chain length and with the side chain length of PDMS. Constant selectivity values were obtained with the number of dimethylsiloxane units > 50. Viscoelastic properties and oxygen permeability of these membranes were measured to clarify the ethanol permselective mechanism. These studies indicate that relationships exist between the glass transition temperature or the oxygen permeability and the permselectivity. That is, ethanol permselectivity increases with a decrease in the glass transition temperature and with an increase in oxygen permeability. These results suggest that the free volume theory for gas can be applied to the permeability of ethanol/water by pervaporation through PDMS membranes. This may be explained by assuring that ethanol and water permeate in the state of vapor since the surface energy of PDMS membranes is very low and the surface is water-repellent.

Blood compatibility of SPUU-PEO-heparin graft copolymers.

Biological responses to heparinized segmented polyurethaneurea (SPUU-PEO-Heparin) were evaluated in vitro and ex vivo. In vitro assays involved plasma protein adsorption, platelet adhesion, and release reaction studies. In addition, an ex vivo rabbit arterio-artery (A-A) shunt experiment was also performed to measure occlusion times of the heparinized surfaces. All SPUU-PEO-Heparin surfaces demonstrated less protein adsorption than Biomer and protein adsorption patterns similar to SPUU-PEO surfaces. Platelet adhesion and release studies demonstrated that both SPUU-PEO-Heparin and SPUU-PEO surfaces adsorbed less platelets and inhibited platelet release, as compared to Biomer. These findings correlated with reduction in protein adsorption observed for the modified surfaces. In low flow rate ex-vivo A-A shunt experiments, all heparinized surfaces prolonged occlusion time longer than controls. However, SPUU-PEO surfaces did not prolong occlusion time when compared to Biomer, although these surfaces suppressed protein adsorption and platelet interaction in vitro. The improved blood compatibility of SPUU-PEO-Heparin surfaces attest to the usefulness of this approach in improving the blood compatibility of blood contacting surfaces.

Interaction of segmented polyurethanes and polyurethane‐ureas with water

AbstractSorption of water vapor by oligomeric homopolymers and triblock copolymers of ethylene oxide and propylene oxide, and by polyurethanes and polyurethane ‐ ureas derived from them is discussed. While the sorption isotherms (plots of ψ1 vs a1, where ψ is he volume fraction of sorbed water and a1 is activity) for most polymers investigated here are smooth and convex towards the abscissa, those found with polyurethane‐ureas containing long hard blocks have a “toe” at low activities. The plots of a1/ψ1 vs a1 are shown to facilitate the analysis of data and the interpretation in terms of the D'Arcy‐Watt theory.Smooth isotherms are fitted by a simple equation with two parameters. The first is related to the limiting value, χ0, (at ψ1 → 0) of the χ parameter characterizing the polymer‐water interaction. The dependences of χ0 on the polymer composition (content of hard segments or oxyethylene units) can provide information on the interaction between hard and soft segments.The second parameter is used in the computation of parameters characterizing the clustering tendency of water molecules. This tendency depends mainly on the content of oxypropylene units but is also raised by urethane or urea groups, though not so much as by oxypropylene groups.

Structure and properties of dry-spun segmented polyurethaneurea elastic fibers

Abstract Influence of the spinning conditions of dry spinning on the structure and properties of segmented polyurethaneurea (SPUU) elastic fibers was investigated in terms of mechanical experiments and infrared analysis. The conditions of dry spinning were estimated by numerical computation. The calculated results were compared with the properties of as-spun SPUU elastic fibers. The structure and properties of as-spun SPUU elastic fibers are highly influenced by the spinning stress, which mainly depends on the throughput (mass flow rate) from an orifice and take-up speed. With an increase of spinning stress, phase mixing between hard and soft segments, orientation of hard segment, and fragmentation of hard segment domains proceed. On the contrary, hard segment domain ordering and the random orientation of soft segment are not influenced by the spinning stress. The change in mechanical properties with the increase of spinning stress can be explained by these morphological changes.

Hydrogen bonding and crystallization behaviour of segmented polyurethaneurea: effects of hard segment concentration

I.r. spectroscopy, d.s.c., WAXD and optical microscopy were employed to investigate the differences between hydrogen bonding and crystallization behaviour depending on hard segment concentration in polyether- and polyester-based polyurethaneureas (PUUs). It has been found that the hard segment crystallization behaviour of polyether-based PUU is higher than polyester-based PUU for the same hard segment content. Hydrogen bonding in polyether-based PUU is formed mainly between hard segments, which promotes crystallization of hard segments. Hydrogen bonding in polyester-based PUU is formed mainly between soft and hard segments, which hinders the crystallization of hard segments.

親水性セグメント化ポリウレタンウレアからの抗菌剤徐放挙動

Blood-compatible segmented polyurethaneureas were evaluated as drug delivery matrices using crystal violet (CV), benzethonium chloride (AC) and acrinol (AC) as model drugs. The polymers were synthesized from ABA-type triblock copolyethers as prepolymers, where A stands for poly (oxyethylene) and B for poly (oxytetramethylene). Microphase separation was observed in the polyurethaneureas, including drug-doped ones. CV dissolved more in the hard segment domains than in the soft segment matrix, whereas BC easily dissolved in the soft segment matrix. AC dissolved in both phases. The drug release behaviors from these polymer films were analysed by the exponent relation Mt/M∞=ktn, where k and n are constants and Mt/M∞ is the fraction of drug released until time, t. The constant k increased with poly (oxyethylene) content, i.e. with the increase of swelling in water. The constant n was found to be ca. 0.5 in many samples, which suggests that the release of drugs from these polymers is explained by the Fickian diffusion model. However, the mechanism became non-Fickian with the increase of swelling of the devices in CV and BC systems. This observation seems to be due to the heterogeneous dissolution of drug in the microphase separated structure.

Synthesis and characterization of SPUU–PEO–heparin graft copolymers

AbstractA new synthetic approach for the preparation of segmented polyurethaneurea (SPUU)–PEO–Heparin graft copolymers (B–PEO–Hep) has been developed. The procedure involved the coupling of hexamethylene diisocyanate (HMDI) to soluble Biomer® (B) through an allophanate/biuret reaction. The free isocyanate (NCO) groups attached to Biomer® were then coupled to PEO terminal hydroxyl groups to form PEO grafted Biomer® (B–PEO). B–PEO free hydroxy groups were modified with HMDI to introduce terminal isocyanate groups. The NCO functionalized B–PEO was then coupled to heparin (Hep) functional groups (OH, NH2) producing B–PEO–Hep graft copolymer. Synthetic intermediates were confirmed by FTIR, NCO group determination, and toluidine blue heparin assay. Physical characterization techniques, such as contact angle measurements, water swelling, light scattering measurements, and DSC thermal analysis, detailed properties of the graft copolymer containing covalently bound heparin. This new heparinized copolymer can be applied as a coating on other existing blood contacting surfaces without changing bulk properties. The heparin bioactivity observed attests to the usefulness of this new procedure as a coating to improve the blood compatibility of blood‐contacting surfaces.

Infrared Dichroism Study of Segmented Polyurethaneurea with Triblock Polyether Soft Segments

Infrared (IR) dichroism study of segmented polyurethaneurea (SEUU) with ABA type triblock copolymer as a soft segment was carried out, where A stands for poly(oxyethylene) (PEO) and B stands for poly(oxytetramethylene) (PTMO). IR dichroism analysis of SEUU films under elongation suggested that the introduction of PEO units to the ends of PTMO brought about more aggregation of the hard segments, i.e., the better microphase separation in SEUU than segmented polyurethaneurea (SPUU) prepared from PTMO. Under uniaxial extension, the crystalline hard segment domain oriented transverse to the stretch direction at early stage, the degree of orientation being larger with the increase of PEO content. The larger was the PEO content, the better the microphase separation in SEUU.

Microphase separation in segmented polyurethaneureas based on poly(oxypropylene) containing poly(oxyethylene) segment (abstract)

Microphase separation in segmented polyurethaneureas based on poly(oxypropylene) containing poly(oxyethylene) segment (abstract)

Modification of polyurethane ureas containing allyloxy groups

Linear segmented polyurethane ureas containing allyloxy groups were modified by reaction with mercaptoethanol. The reaction was followed using elemental analysis and 1H NMR. The mechanical properties of these modified polymers were improved, and their hydrophilicity was enhanced. The polyurethane ureas modified by mercaptoethanol were further reacted with 4,4′-diphenylmethane diisocyanate and polyethyleneglycol to form comb-like blocks with pendant hydroxyl groups. These reactions were followed using 1H and 13C NMR. The modified polyurethane ureas were further characterized using SEC, mechanical analysis and water-uptake tests.

Sequence Distribution of Segmented Polyurethane-Urea

Segmented polyurethane-urea (SPU) elastomer was prepared from poly-tetramethyleneglycol (PTMG), 4,4′-diphenylmethane diisocyanate (MDI), and ethylenediamine (EDA). The SPU is a kind of block copolymer composed of soft and hard segments. 13C NMR spectra of the SPU were measured and the mean sequence lengths of polyurethane block and polyurea block were estimated from the signals of aromatic carbons. The mean polyurea sequence length was shorter than the hard segment as estimated by X-ray diffraction (Kimura et al.) or by other methods (Suzuki et al.). This polymer was found to be almost a random copolymer. The reactivity of the isocyanate group in MDI decreases slightly when the other side of isocyanate has reacted. The hard segment observed by X-ray diffraction or by other methods might only be the longer fraction of polyurea sequences.

Polyurethane elastomer with PEO-PTMO-PEO soft segment for sustained release of drugs

Blood-compatible segmented polyurethanes and polyurethaneureas were evaluated as drug delivery matrices using crystal violet and benzethonium chloride as model drugs. These polymers were synthesized from ABA-type triblock copolyether as a prepolymer, where A stands for polyethylene oxide) and B for polyftetramethylene oxide). Microphase separation was observed in segmented polyurethaneureas, including drug-doped films. Crystal violet dissolved more in the hard segment domain than in the soft segment matrix, whereas benzethonium chloride was easily dissolved in the soft segment matrix. The drug release behaviours from these films were analysed by the exponent relation M/M∞ = ktn, where k and n are constants and MtM∞ is the fraction of drug released until time, t. The constant k grew with increasing poly(ethylene oxide) content in the prepolymer, i.e. increased swelling. The constant n was found to be close to 0.5 in many samples, which suggests the release of drug from these polymers is explained by the Fickian diffusion model. However, the mechanism became non-Fickian with increased swelling of the devices.