Segmented Poly Urethane-urea Research Articles

Ultra small-angle X-ray scattering studies on structural changes in micrometers upon uniaxial stretching of segmented polyurethaneureas

Ultra small-angle X-ray scattering (USAXS) experiments were conducted in order to examine structural changes in micrometers upon uniaxial stretching of elastomeric segmented polyurethaneureas at room temperature. It was possible to stretch the sample film up to α=7.5 without break, where α designates the stretching ratio. Around α=6.5 the sample became turbid, while it recovered transparency when the stress was removed. To understand this curious phenomenon, we conducted the USAXS experiments for the structural analyses in micrometers. Although a set of streaks appeared in the direction parallel to the stretching direction (SD) when the sample became turbid (around α=7.2), more interesting result is that a set of streaks appeared in the direction perpendicular to SD much earlier around α=5.0. Close examination of the scattering intensity profile revealed evolution of multiple interference peaks, which could be ascribed to the form factor of a lamellar particle. Since the streaks disappeared upon the removal of the stress, “lamellar particles” are considered to be crazes, which develop further into cracks in a subsequent stage. From the results of USAXS measurements, it is suggested that the lamellar-shaped crazes appeared around α=5.0 being oriented parallel to SD, and further stretching created other lamellar-shaped crazes being oriented perpendicular to SD, which are co-existing with the preceding parallel crazes.

Synthesis and characterization of semi‐interpenetrating polymer networks based on polyurethane and N‐isopropylacrylamide for wound dressing

Thermosensitive semi-interpenetrating polymer networks (semi-IPNs) composed of crosslinked poly(N-isopropylacrylamide) (PNiPAAm) and linear segmented polyurethane urea (SPUU) were synthesized via thermal initiated free radical polymerization. Synthesized semi-IPNs of various compositions were characterized by Fourier transform infrared spectroscopy, water equilibrium swelling at different temperatures, drug lading, drug release, cell adhesion, and detachment. The semi-IPN films of all the compositions were transparent in dry state and negative thermosensitivity in their swelling ratio, that is, lower swelling levels with increasing temperature. The drug release study revealed that the rate of drug release is fast in case of pure SPUU compared to PNiPAAm and semi-IPN film. Drug release depended mainly on solubility of the drugs and physical networks between SPUU and PNiPAAm. Finally NIH3T3 cells were seeded on the semi-IPN films and found that cells were securely attached and proliferated to confluence. Upon cooling, cells were detached from the semi-IPN films. Therefore, the semi-IPN films may be good candidate materials for wound dressing applications.

Nanostructured poly(urethane)s and poly(urethane-urea)s from reactive solutions of poly[styrene- b-butadiene- b-(methyl methacrylate)]-triblock copolymers

Poly[Styrene- b-Butadiene- b-(Methyl Methacrylate)], SBM triblock copolymers have been incorporated in different polyurethane, PU formulations in order to prepare nanostructured materials. Macrodiols used for PU synthesis were based on a central bis-phenol A, BPA unit with two hydroxyl-terminated oligo(oxypropylene), BPA-PO x or oligo(oxyethylene), BPA-EO chains with varying lengths. The initial solubility of the three blocks and the rheological behavior of the solutions in macrodiols and also in two diisocyanates, isophorone diisocyanate, IPDI, and 1,3-xylylene diisocyanate, XDI have been first characterized. The PMMA block is the most soluble and its role during the reaction is to stabilize the initial nanostructure or to control the reaction-induced microphase separation. Block copolymers can be dissolved first in the macrodiol, or preferably in the diisocyanate. With BPA-PO x and low SBM content (<10 wt%), transparent linear or crosslinked PU with well dispersed triblock nanoparticles have been prepared, depending on the molar mass of the macrodiol and on the concentration of diblock SB impurities present in the triblock. For high SBM concentrations (>50 wt%), a twin screw extruder had to be used for the blending. Under well-defined conditions, transparent linear PUs and linear segmented polyurethane-ureas have been prepared. This study confirms that for designing a nanostructured material from a reactive mixture with a triblock additive, one block, called “the nanostructuring block” has to remain soluble up to the end of the reaction.

Enzymatic hydrolysis of lysine diisocyanate based polyurethanes and segmented polyurethane ureas by various proteases

This work studies the enzymatic degradation of polyurethanes (PUs) and segmented polyurethane ureas (SPUUs) derived from lysine diisocyanate (LDI) by various proteases. Thiol proteases, such as papain, bromelain, and ficin, showed high activity on PUs. Protease K and chymotrypsin also hydrolyzed the PUs. For almost all SPUUs, papain showed high activity. For example, LDI/poly(caprolactone) diol ( M w = 1250)/ethylene diamine (2/1/1) was hydrolyzed to 43% under the same conditions. The water-soluble degradation products of a polyurethane, LDI/BD (1/1), and two model compounds treated with papain were studied with NMR and GPC analysis. From the results, it was evident that the pendant methyl ester group in LDI was rapidly hydrolyzed, followed by slow hydrolysis of urethane bonds in the backbone chain.

Controlled Release of Model Drug from Biodegradable Segmented Polyurethane Ureas: Morphological and Structural Features

AbstractSegmented polyurethane ureas (SPUUs), which are being used in implant devices, were evaluated as drug delivery matrices using theophylline as a model drug without much sacrificing the mechanical properties of films after drug doping. SPUUs were synthesized from aliphatic diisocyanate (lysine methyl ester diisocyante (LDI)), poly(caprolactone) diol with molecular weights 530, 1250 and 2000 and 1,4‐butanediamine. Three series of segmented SPUUs were prepared with various soft segment lengths and were characterized by Fourier transform infrared spectroscopy, dynamic viscoelastic measurements and tensile testing. A single tanδ peak was observed in dynamic viscoelastic measurements, which revealed phase mixing of hard and soft segments. Low elongation at break was observed in case of PCL 2000 based SPUUs, may be due to partial cystallization of PCL segment. The degradation of SPUUs in alkaline solution and in vitro drug release of theophylline in pH 7.4 buffer were also investigated. The drug release behavior from these films were analyzed 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 n was found to be close to 0.5 in all samples, which suggests the release of drug from these polymers can be explained by the Fickian diffusion model.

Deformation Behaviour of Segmented Polyurethaneureas

Deformation Behaviour of Segmented Polyurethaneureas

Structure–property behavior of segmented polyurethaneurea copolymers based on an ethylene–butylene soft segment

Novel segmented polyurethaneurea copolymers were synthesized using a poly(ethylene–butylene) glycol based soft segment and either hydrogenated diphenyl methane diisocyanate (HMDI) or hexamethylene diisocyanate (HDI) in addition to either ethylene diamine (EDA) or 2-methyl-1,5-diaminopentane (DY) as the chain extender. Dynamic mechanical analysis (DMA), small angle X-ray scattering (SAXS) and in some cases atomic force microscopy (AFM) established the presence of a microphase-separated structure in which hard microdomains are dispersed throughout a soft segment matrix. Wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) imply that the materials are amorphous. Samples that are made with HMDI/DY and have hard segment contents in the range of 16–23 wt% surprisingly exhibit near-linear mechanical deformation behavior in excess of 600% elongation. They also show very high levels of recoverability even though their hysteresis is also considerable. The materials have all proven to be melt processable in addition to solution processable.

Kinetics of Sorption of Organic Liquids by Segmented Polyurethane Urea

Kinetics of Sorption of Organic Liquids by Segmented Polyurethane Urea

Understanding the structure development in hyperbranched polymers prepared by oligomeric A 2+B 3 approach: comparison of experimental results and simulations

Structure development in highly branched segmented polyurethaneureas based on oligomeric A 2+B 3 approach was investigated by experimental studies and kinetic Monte-Carlo simulations. In both simulations and experiments, hyperbranched polymers were produced by the slow addition of A 2 onto B 3. Experimental studies showed strong influence of solution concentration on the gel point and the extent of cyclization in the polymers formed. In polymerizations conducted at a solution concentration of 25% by weight gelation took place at the stoichiometric ratio [A 2]/[B 3]=0.886. This is somewhat higher than the theoretical ratio of 0.75. In very dilute solutions, such as 5% solids by weight, no gelation was observed although the stoichiometric amount of A 2 added well exceeded the theoretical amount for gelation. Both experimental studies by size exclusion chromatography (SEC) and kinetic Monte-Carlo simulations demonstrated a gradual increase in polymer molecular weights as more A 2 is added onto B 3. This was followed by a sharp increase in the polymer molecular weight as the gel point is approached. A very similar behavior was observed for the polydispersity values of the polymers formed. Kinetic Monte-Carlo simulations performed at different cyclization ratios showed very good agreement with experimental results.

Waterborne anionomeric polyurethane–ureas from functionalized fluoropolyethers

AbstractA family of anionomeric segmented polyurethane–ureas made from α‐ω dimethylol‐terminated perfluoropolyethers (Mn = 1000–2000), isophorone diisocyanate, dimethylol propionic acid, and ethylenediamine was obtained in form of stable aqueous dispersions. The dispersions were characterized by viscometry and dynamic laser light scattering. The main compositive parameters explored were the amount of COOH groups and the length of the fluorinated macromer. The new polyurethane–ureas were characterized by dynamic mechanical analysis obtaining information on modulus, thermal transition, and phase segregation. Surface properties and chemical resistance were estimated through measurements of static contact angles and spot tests with different solvents. Although surface hydrophobicity was not affected by composition, water‐sorption behavior was sensitive to the ionic character (COOH level) of the polymer. Diffusion and permeability coefficients of polymer films, having different carboxyl contents, were estimated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 136–144, 2004

Synthesis, Characterization and Properties of 2‐(Perfluorooctyl)ethylacrylate Grafted Segmented Polyurethaneureas

AbstractWe report herein that 2‐(perfluorooctyl)ethylacrylate (PFEA) was successfully grafted onto a segmented polyurethaneurea (SPUU). We found that certain PFEA orientated onto the grafted SPUU film surface could significantly improve hemocompatibility. 1,2‐Propanediamine (PD) as a chain extender was used to synthesize the SPUU, which was based on diphenylmethane diisocyanate (MDI), vinyl group‐containing poly(butadiene) diol (PBD), and hydrogenated poly(isoprene) diol (HPIP). PFEA was copolymerized with the SPUU using α,α′‐azobis(isobutyronitrile) (AIBN) as a radical initiator. Various feed ratios of PFEA grafted polymers were synthesized (SPUU‐F‐0.5, SPUU‐F‐0.75, and SPUU‐F‐1.0) while non‐grafted SPUU was abbreviated as NG‐SPUU. The bulk characteristics of the resulting polymers were investigated by infrared spectroscopy (IR) measurement. Mechanical properties of the typical PFEA grafted SPUU were measured by dynamic viscoelasticity and tensile measurements. We found that PFEA orientated on the surface, as revealed by attenuated total reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR), electron spectroscopy for chemical analysis (ESCA), and water contact angle measurements. The hemocompatibility in vitro was evaluated with rabbit platelet‐rich plasma (PRP) contact tests and viewed by electron probe microanalyzer (EPM) using NG‐SPUU as a reference. We found that fewer platelets adhered to the PFEA grafted surfaces. New polymer SPUU‐F‐0.5 showed the best hemocompatibility in the tested samples. Platelet adhesion to PFEA grafted polymers SPUU‐F‐0.5, SPUU‐F‐0.75, and SPUU‐F‐1.0 was inhibited 91%, 58%, and 50% compared with NG‐SPUU. The relative clotting time of the cast films in contact with cow platelet‐poor plasma (PPP) was 3.26, 2.94, 1.95, 2.39 and 1.00 for SPUU‐F‐0.5, SPUU‐F‐0.75, SPUU‐F‐1.0, NG‐SPUU, and glass, respectively. The new polymers also showed the common characters of fluorinated polymers as revealed by water vapor transmission, dielectric constant, and index of refraction measurements.Structure of the synthesized PFEA Grafted SPUU.magnified imageStructure of the synthesized PFEA Grafted SPUU.

High‐Throughput Screening of Mechanical Properties on Temperature‐Gradient Polyurethaneurea Libraries

AbstractCombinatorial libraries of segmented polyurethaneurea with gradients in curing temperature were prepared and characterized using a novel high‐throughput mechanical instrument. Stress/strain profiles were taken at different temperature positions on the libraries, and a structure/property relationship between microstructure and mechanical properties was established by correlating the measured strength and strain at break to high‐throughput AFM and FT‐IR measurements on the same library. These results demonstrate the feasibility of rapid and accurate screening of mechanical properties, and their correlation to structure, by using gradient combinatorial polymer libraries. Impact energy/thickness and elongation at break versus cure T for a T‐gradient SPUU library.magnified imageImpact energy/thickness and elongation at break versus cure T for a T‐gradient SPUU library.

Separation of toluene/nitrogen through segmented polyurethane and polyurethane urea membranes with different soft segments

Segmented polyurethane and polyurethane urea, containing soft segments such as polydimethylsiloxane (PDMS), polytetramethylene oxide (PTMO), and polyethylene oxide-polypropylene oxide triblock copolymer (PEO–PPO–PEO), were synthesized with a wide range of monomer concentrations. Dense membranes with 30–40 μm in thickness prepared by casting 20 wt.% N, N-dimethylformamide (DMF) solutions onto glass plate were examined for the separation of toluene vapor from nitrogen stream. Equilibrium liquid sorption behaviors of synthetic membranes were carried out by determining the amount of liquid toluene absorbed in the films at 25 °C. The vapor permeability of toluene through the PTMO/PDMS based polyurethane urea membranes were higher than those measured in PEO–PPO–PEO based polyurethane membranes due to plasticization by toluene vapor. In the case of the PTMO/PDMS based polyurethane urea membranes, the permeability of nitrogen increased and then the toluene/N 2 selectivity was lowered relative to those for PEO–PPO–PEO based polyurethane membranes due to plasticization of polymer. Up to the feed-flow rate of 250 ml min −1, the toluene fluxes obtained in all the membranes showed a linear dependence on the saturated feed concentration. The polyurethane urea membranes containing PTMO/PDMS mixed soft segment performed best with toluene separation, with toluene/N 2 selectivity ranging from 70 to 140 and the pressure-normalized permeability as high as 17,500 Barrer when the saturated toluene feeds were operated at 25 °C and a downstream pressure of 0.5 cmHg.

Identification of biodegradation products formed by L-phenylalanine based segmented polyurethaneureas

The degradation of novel biodegradable segmented polyurethanes was investigated with a view to determining the cleavage points within the polymer backbones targeted by the enzyme chymotrypsin. While the materials were developed with specific enzyme cleavage sites designed into the polymer chains, the nature of their degradation had not yet been determined. In this work, two segmented polyurethaneureas containing L-phenylalanine residues in the chain extender and two control polymers were subjected to degradation in the presence of chymotrypsin. Samples were collected for analysis over a time period from 1 day to 8 weeks. The degradation products from these materials were isolated using solid phase extraction and reversed phase high pressure liquid chromatography, and identified using mass and tandem mass spectrometry. Three hard segment related degradation products were identified and provide important insight into the polyurethane backbone cleavage sites. Cleavage of urea, ester and urethane bonds were observed. The results confirmed that chymotrypsin was able to cleave ester bonds adjacent to phenylalanine residues contained within the novel chain extender.

Hydrophilic hybrid IPNs of segmented polyurethanes and copolymers of vinylpyrrolidone for applications in medicine

The preparation and biocompatibility properties of thermoplastic apparent interpenetrating polymer networks (T-IPNs) of a segmented polyurethaneurea, Biospan™ (BS), and vinylpyrrolidone–dimethylacrylamide (VP–DMAm) copolymers, are described. The biological interaction between the obtained materials and blood was studied by in vitro methods. The addition of the VP–DMAm copolymers to form T-IPNs with BS substantially increased the equilibrium water uptake and water diffusion coefficients. Investigation of the proteins adsorption, platelet adhesion, thrombus formation and factor XII activation is presented. Investigations of the proteins adsorption of the BS/VP–DMAm T-IPNs surfaces show that the segmented polyurethane (BS) containing VP–DMAm copolymers with higher VP content adsorb more albumin than fibrinogen and γ-globulin. The platelets adhesion, thrombus formation and factor XII activation are effectively suppressed with respect to the segmented polyurethane when VP–DMAm copolymers with high VP contents are incorporated into BS as T-IPNs.

Segregation Processes in Segmented Polyurethaneurea Solutions Observed by Fluorescence Depolarization

The onset of a segregation process in segmented polyurethaneurea (SPUU) solutions was studied by fluorescence spectroscopy using free fluorescein as a probe. For SPUUs with a given molecular weight and a constant ratio of the hard to soft segments, the time-resolved fluorescence measurements reveal the environmental inhomogeneity on the excited lifetime of fluorescein. It is shown in this work that the critical concentration for the segregation process detected by fluorescence spectroscopy through the transition of the anisotropy ratio of the fluorescein occurs at a concentration lower than that observed by small angle X-ray scattering (SAXS). These experimental results indicate that fluorescence depolarization can be used as an alternative method to investigate the structural transition in SPUU solutions.

Hydrophilic polyurethaneurea membranes: influence of soft block composition on the water vapor permeation rates

High molecular weight segmented polyurethaneurea (PUU) copolymers based on an aliphatic diisocyanate, bis(4-isocyanatocyclohexyl)methane and mixed hydrophilic and hydrophobic soft segments were prepared. Hydrophilic blocks consisted of poly(ethyleneoxide) (PEO) of molecular weight 1450 g/mol, whereas the hydrophobic blocks were poly(tetramethylene oxide) of molecular weight 2000 g/mol. Ethylene diamine was used as the chain extender. Hard segment contents of the copolymers were kept constant at 18%, whereas PEO contents were varied between 0% and 50% by weight. Water vapor permeation rates (WVPR) of thin films (23–178 μm) cast from dimethylformamide solutions were determined. In studies performed at 23°C and 50% relative humidity, the relationship between PEO content and WVPR followed an S-shaped curve. For copolymers containing up to about 15% by weight of PEO, WVPR were fairly low. This was followed by a region where WVPR increased continuously for membranes containing between 15% and 30% PEO. Further increase in PEO content above 30% did not influence the WVPR substantially. There was also a dramatic increase in WVPR with an increase in temperature from 23°C to 37°C. Activation energy of permeation was determined to be 91.5 kJ for PUU containing 22.0% by weight of PEO. Equilibrium water absorption levels of PUU containing different levels of PEO in their backbone structures followed a similar trend to that of WVPR. Hydrophilic PUUs showed good tensile properties and mechanical integrity even at very high levels of water absorption.

New segmented polyurethane ureas based on 4,4?-dicyclohexylmethane diisocyanate and on various soft segments

Linear segmented polyurethane ureas were prepared from 4,4′-dicyclohexylmethane diisocyanate (H12MDI), 4,4′-diamino-3,3′-dicyclohexyl methane (3DCM), and various hydrophilic and hydrophobic soft segments. Kinetic studies of the synthesis of the diisocyanate-terminated prepolymers revealed that the use of too little reactive polyols (that is, polyoxypropylene that bears secondary hydroxyls) could be rather tricky; the noncatalyzed reaction is very slow, but the use of a catalyst soon triggers the formation of side products, and the processing window consequently becomes quite short. Microcalorimetric and dynamic mechanical measurements showed that all the materials were highly phase-segregated elastomers and displayed good mechanical properties up to high temperature (typically 180°C), provided that they had been postcured properly; in this respect, the dramatic effects of isolated (nonchemically linked) hard segments, as well as of too low postcuring temperatures, were demonstrated. Polyurethane ureas compare well with polyureas, and their synthesis can be a good way to cope with the lack of well-adapted commercial diamino-terminated prepolymers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2331–2342, 1998

SAXS and dynamic viscoelastic studies on segmented polyurethaneurea solutions

The microstructure and dynamic mechanical properties of segmented polyurethaneurea (SPUU) in concentrated dimethyl acetamide (DMAc) solutions have been investigated by means of small-angle X-ray scattering (SAXS) and viscoelastic measurements, respectively. Kratky plots of SAXS intensity functions indicated the following: (1) Formation of hard segment domains introduced mainly by hydrogen bondings is promoted with increasing ratio of isocyanate to hydroxyl groups ([NCO]/[OH]) and polymer concentration, C p. (2) The degree of completion of the hard segment domains increases with temperature up to 55°C and then gradually decreases by further increase of temperature. An analogy was found between [NCO]/[OH] dependence of the dynamic storage G′( ω) and loss shear moduli G″( ω) for SPUU in DMAc and time dependence of those for a chemically gelling system. G′( ω) and G″( ω) indicated that the properties of SPUU solutions change from sol-like to gel-like with increasing [NCO]/[OH]. By varying [NCO]/[OH], a relationship of G′( ω) ≈ G″( ω) ≈ ω k was observed around [NCO]/[OH] = 1.6. The exponent k is evaluated to be 0.67, which was similar to the literature value obtained at the gelation point. This corresponds to the ‘gelation threshold’ of the chemical gelation process.

Elastic properties of real elastomers at small deformations

AbstractElastic properties of real elastomers were examined by using partial derivatives of the strain energy density function (W) with respect to the invariant (Ii, i=1,2,3) of deformation tensor. The values of the derivatives at zero strain limit for styrene‐butadiene rubber (SBR), nitrile‐butadiene rubber (NBR) and butadiene rubber (BR) were compared with those derived from the theory shown in the previous paper, where compressibility of the materials was taken into account. The asymptotic behavior of the derivatives for isoprene rubber (IR) and segmented polyurethaneurea (SPU) was also compared with those of the three types of rubbers. It was shown that the theoretical predictions for the limiting value agreed fairly well with the experimental values of the elastomers.