Bi-soft Segment Research Articles

Imparting Reprocessability, Quadruple Shape Memory, Self-Healing, and Vibration Damping Characteristics to a Thermosetting Poly(urethane-urea)

The advent of dynamic covalent bond chemistry (DCBC) has sparked renewed research interest in reprocessability of thermosetting polymers. However, combining reprocessability with stimuli-responsiveness remains a challenge for futuristic applications. Usually, a combination of complementary DCBCs is employed to integrate reprocessability with shape memory as well as self-healing (SH) attributes in a single polymeric system. In the present work, we report two-component poly(urethane-urea) (PUU) networks, with varied hard segment (HS) concentrations, that exhibit quadruple shape memory (QSM), efficacious vibration damping, thermally activated intrinsic SH as well as multiple cycles of thermal reprocessability. The component A is an isocyanate capped bi-soft segment blend of polybutadiene diol and polypropylene glycol, while the second component comprises an aromatic diamine chain extender solubilized in an oligomeric polyoxypropylene triol. The networks characterized through FTIR as well as small- and wide-angle X-ray scattering (SAXS and WAXD) revealed a phase-separated morphology with extensive hydrogen-bonding (H-bonding) interactions in the HS domains of the PUU networks. Dynamic mechanical analysis (DMA) measurements revealed broad dissipation factor (tan δ) vs temperature and frequency profiles of the networks, which could be leveraged for efficacious passive vibration damping applications. A dissociative mechanism of urethane and urea bond exchange, evidenced from temperature-dependent FTIR studies enabling facile stress relaxation, is proposed to be the mechanistic origin of the reprocessability and SH of the networks. A broad dissipation factor (tan δ) vs temperature profiles endowed the networks with QSM characteristics. We posit that the study is relevant for expanding the scope of DCBCs for development of reprocessable thermosetting polyurethanes with multiple smart functionalities.

Sorption/Diffusion Contributions to the Gas Permeation Properties of Bi-Soft Segment Polyurethane/Polycaprolactone Membranes for Membrane Blood Oxygenators.

Due to their high hemocompatibility and gas permeation capacity, bi-soft segment polyurethane/polycaprolactone (PU/PCL) polymers are promising materials for use in membrane blood oxygenators. In this work, both nonporous symmetric and integral asymmetric PU/PCL membranes were synthesized, and the permeation properties of the atmospheric gases N2, O2, and CO2 through these membranes were experimentally determined using a new custom-built gas permeation apparatus. Permeate pressure vs. time curves were obtained at 37.0 °C and gas feed pressures up to 5 bar. Fluxes, permeances, and permeability coefficients were determined from the steady-state part of the curves, and the diffusion and sorption coefficients were estimated from the analysis of the transient state using the time-lag method. Independent measurements of the sorption coefficients of the three gases were performed, under equilibrium conditions, in order to validate the new setup and procedure. This work shows that the gas sorption in the PU/PCL polymers is the dominant factor for the permeation properties of the atmospheric gases in these membranes.

Evidence of Liquid-Liquid Demixing During Bi-Soft Segment Polyurethane Prepolymerization

Bi-soft segment isocyanate-terminated polyurethanes (ITPUs) currently play a major role in the industrial production of high performance polyurethanes (adhesives, coating, foams, thermoplastics, nanoparticles, dispersion). The present contribution reports on the investigation of liquid-liquid demixing phenomena during the synthesis of bi-soft segment ITPUs. For this purpose, a dedicated experimental setup based on coupled in-line reaction monitoring via UV/Vis and FTIR technique was developed. It was used to monitor phase separation and reaction progress in the course of a prepolymerization using 1,6-hexamethylene diisocyanate and a polyether polyol mixture. Such phenomena may have a great impact on reaction kinetics and product quality. Furthermore, in-line FTIR analysis appeared to be sensitive to phase separation processes in the way that it predominantly detects the continuous phase rather than the dispersed droplets.

Phase segregation and gas permeation properties of poly(urethane urea) bi-soft segment membranes

Segmented poly (urethane urea) membranes, containing two soft segments, poly(propylene oxide) and poly(caprolactone), were prepared by extending a poly(propylene oxide) based tri-isocyanated prepolymer with poly(caprolactone) diol. The membranes synthesized with poly(caprolactone) diol content ranging from 0wt.% to 15wt.% were characterized by infrared spectroscopy (ATR-FTIR). It was concluded that the urethane groups form hard segment aggregates dispersed in the soft segment phase and that this aggregation increases with the increase of poly(caprolactone) content. Gas permeation experiments performed by a photoacoustic system led to the conclusion that permeabilities of CO2 increased from 188 Barrer to 337 Barrer when the poly(caprolactone) membrane content increased from 0wt.% to 10wt.% and was lowest, 113 Barrer, for the membrane containing 15wt.% of PCL. The permeability of O2 through the membranes was independent of poly(caprolactone) content and was between 10 and 11 Barrer. The membrane with the highest CO2 permeability contains 10wt.% of poly(caprolactone) and is characterized by the highest contribution of hydrogen bonding between urethane and urea hard segments.

Surface Characterization of Asymmetric Bi-Soft Segment Poly(ester urethane urea) Membranes for Blood-Oxygenation Medical Devices

Asymmetric bi-soft segment poly(ester urethane urea) (PEUU) membranes containing polycaprolactone (PCL) as a second soft segment are synthesized with PCL-diol ranging from 0% to 15% (w/w). Bulk and surface characteristics of the PEUU membranes were investigated by scanning electron microscopy (SEM), static water contact angles, and surface streaming potentials and were correlated to hemocompatibility properties, namely, hemolysis and thrombosis degrees. SEM analysis reveals PEUU membranes with asymmetric cross-sections and top dense surfaces with distinct morphologies. The increase in PCL-diol content yields PEUU membranes with blood-contacting surfaces that are smoother, more hydrophilic, and with higher maximum zeta potentials. The results obtained in this work give no evidence of a correlation between hydrophilicity/zeta potentials and the hemolysis/thrombosis degree of blood-contacting surfaces of the PEUU membranes. In contrast, other hemocompatibility aspects reveal that the more hydrophilic membranes are associated with lower platelet deposition and inhibition of extreme states of platelet activation.

Tailoring bi-soft segment poly (ester urethane urea) integral asymmetric membranes for CO 2 and O 2 permeation

Integral asymmetric bi-soft segment poly (ester urethane urea) membranes are casted through a novel procedure where a reaction is introduced in the casting solutions preparation step of the phase inversion technique. Two reactive pre-polymers, the polypropylene oxide-based with three terminal isocyanate groups and the polycaprolactone diol with two terminal hydroxyl groups, are dissolved in a single solvent, dimethyl formamide and in a solvent mixture of dimethyl formamide (DMF)/diethyl ether (DEE) and the polymerization reaction is carried out in a homogeneous phase. The weight ratio of DMF/DEE is varied over 11, 5 and 3. The membrane casting is carried out at solvent evaporation times of 30 s, 60 s and 90 s. For all the membranes prepared, the cross-sections of the scanning electron microscopy (SEM) images display asymmetric structures dependent on the casting solutions composition and on the casting evaporation times. The carbon dioxide and oxygen volumetric fluxes measured at pressures ranging from 76 cmHg to 380 cmHg were correlated to the active layer thickness of the asymmetric membranes. The achievement of increasing the O 2 and the CO 2 permeation rates is the result of the casting of poly (ester urethane urea) asymmetric membranes with the minimization of the thickness of the dense layers. This is coupled with the introduction of the reactive caprolactone pre-polymer that enhances hemocompatibility. These are two strong assets for membrane blood oxygenators.

Sub-micron tailoring of bi-soft segment asymmetric polyurethane membrane surfaces with enhanced hemocompatibility properties

Enhancement of membrane hemocompatibility is achieved through the control of the surface morphology. Bi-soft segment integrally skinned poly(ester urethane urea) (PEUU) membranes containing polycaprolactone (PCL) as a second soft segment are synthesized with PCL-diol ranging from 0% to 15% (w/w). Scanning electron microscopy and atomic force microscopy characterized membrane asymmetry and sub-micron roughnesses, R(a), of top dense surfaces as major assets to the development of platelet/membrane surface interactions. Here we show that the top dense surfaces of asymmetric PEUU membranes can be tailored with different morphologies when the ratio of the two soft segments PPO/PCL varies. A strong correlation between the top surface roughnesses, R(a) and platelet deposition is identified. The membrane with 15% (w/w) of PCL-diol, PEUU 85, shows the smoothest top dense layer with a R(a) as low as 1 nm which is 5 times below the characteristic value of the PEUU membrane with a single soft segment. The PEUU 85 asymmetric membrane displayed minimal platelet deposition and inhibition of extreme stages of platelet activation.

Characterization and in vitro hemocompatibility of bi‐soft segment, polycaprolactone‐based poly(ester urethane urea) membranes

In this study, surface, bulk, and hemocompatibility characteristics of crosslinked, bi-soft segment poly (ester urethane urea) membranes, prepared by extending a poly(propylene oxide)-based triisocyanate-terminated prepolymer (PU) with a polycaprolactone diol (PCL), were investigated. Variation of the ratio of PU to PCL diol content in the membrane formulation yielded alteration of surface energy, phase morphology both in the bulk and in the region near the surface, and it affected hemocompatibility. Nearly all membranes were nonhemolytic, with hemolysis degrees between 1 and 2.1% and, for short-time contact with blood (15 min), all membranes showed in vitro thrombosis degrees between 27 and 42%. The membranes prepared with 5 and 25% of PCL diol showed almost no adherent platelets. These two membranes had a higher hard segment aggregation in the region near the surface and mixing between the two soft segments in the bulk, but showed contrasting surface energy characteristics. The results obtained in this work give evidence that surface energy and its polar and dispersive components did not correlate with any of the hemocompatibility aspects studied. In contrast, the phase morphology in the region near the surface was a major influence on membrane hemocompatibility.

Surface and Hemocompatibility Studies of Bi-Soft Segment Polyurethane Membranes

Cross-linked urethane/urea membranes with two soft segments were prepared by extending a poly(propylene oxide) based tri-isocyanate-terminated prepolymer (PUR) with polybutadiene diol (PBDO). The ratio of prepolymer and polybutadiene diol was varied to yield cross-linked membranes with different compositions, exhibiting different degrees of phase-separation of the PBDO segments in the bulk and of surface enrichment in PUR. In this work, surface energy and hemocompatibility aspects (hemolysis and thrombosis) of the PUR/PBDO membranes were evaluated. The results showed that the membrane surface energy increased with the PBDO content until 25% of PBDO, and decreased thereafter. The introduction of the second, more hydrophobic, soft segment (PBDO) in the PUR membranes turned hemolytic into non-hemolytic membranes and, for a blood-material contact time of 10 minutes, decreased the thrombogenicity significantly. The 10% PBDO membrane was the least thrombogenic and was also non-hemolytic. The hemolysis degree did not vary significantly with the PBDO content while, for blood-material contact times of 10 minutes, the thrombogenicity increased with an increase in PBDO content above 10%. Membrane thrombogenicity varied with the blood-material contact time. For blood contact times of 10 minutes, all membranes tested were less thrombogenic than glass.

Positron studies of the temperature-dependence of free volumes in Polydimethylsiloxane/poly(propylene oxide) urethane/urea membranes

Free-volume parameters in polyurethane/urea membranes have been studied by positron annihilation lifetime and Doppler broadening measurements. The bi-soft segment membranes were obtained by varying the ratio of the structural constituents, polypropylene oxide and polydimethylsiloxane (PU/PDMS), with PDMS content from 25 to 75 wt%. The free-volume holes determined by PALS are correlated with gas permeation features. The phase separation of the various soft and hard segments in the membranes is mirrored in both lifetime and Doppler results.

Pattern Formation in a Bi-Soft Segment Urethane Elastomer

In the present work we study pattern formation in a bi-soft segment urethane/urea elastomer. The material under study is a film prepared from a polypropylene oxide based isocyanate terminated triol prepolymer (PU) and polybutadiene diol (PBDO) with 60% by weight of PBDO. Small angle light scattering (SALS) patterns were recorded as a function of elongation for different rates of extension. It was found that the process of band and stripe formation is dependent upon the sample elongation and rate of extension with a strong increase of band and stripe amplitude with increasing elongation. The SALS data also reveals that the bands' periodicity is independent of the rate of extension within the range studied.

Free-volume studies in polyurethane membranes by positron annihilation spectroscopy

The free-volume parameters in various urethane/urea membranes obtained by varying the ratio of the structural constituents, polypropylene oxide and polybutadiene, were studied by positron lifetime and Doppler broadening measurements. On bi-soft segment membranes, a correlation was found between the composition of membranes, the normalized free volume, the radii of the holes and gas permeability. However, the correlation is not clear when PU data are also considered, indicating that other features must also play an important role in the permeation mechanism.

Shear-Induced Order Effects in Bi-Soft Segment Urethane/Urea Elastomers

In this work we study shear-induced order effects, observed on thin films (∼20–60 μm) of urethane/urea elastomers prepared from a polypropylene oxide based isocyanate terminated triol prepolymer (PU) and polybutadiene diol (PBDO) in the amount of 25% (PU/25PBDO), 50% (PU/50PBDO), 60% (PU/60PBDO) and 75% (PU/75PBDO) by weight of polybutadiene. Optical microscopy and light scattering as a function of temperature were used in this study. The initial isotropic elastomers, PU/60PBDO and PU/75PBDO, after cessation of a uniaxial mechanical deformation relax to a band texture, consisting of equidistant bright and black lines perpendicular to the shear direction. If the uniaxial mechanical stress is applied again perpendicular to the band structure in PU/60PBDO, a new periodicity with wave vector perpendicular to the axis of the field develops, while for PU/75PBDO two new periodicities can be observed, one with wave vector perpendicular to the axis of the field and the other transverse. The process of band formation is completely reversible in cycles of increasing and decreasing strain ratios. In samples PU/25PBDO and PU/50PBDO this kind of effect is not observed. The bands periodicity is temperature independent. The temperature dependence of the scattered intensity produced by the bands is different for bands perpendicular and transverse to the axis of the stress field. We show evidence that the urethane linkage is responsible for the relaxation instabilities observed, in this kind of material.

Mechanico-Optical Effects in a Polypropylene Oxide/Polybutadiene Bi-Soft Segment Urethane/Urea Elastomer

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTMechanico-Optical Effects in a Polypropylene Oxide/Polybutadiene Bi-Soft Segment Urethane/Urea ElastomerM. H. Godinho, J. L. Figueirinhas, C.-T. Zhao, and M. N. de PinhoView Author Information Department Ciência dos Materiais and CENIMAT, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2825-114 Monte da Caparica, Portugal; Department de Física and Department de Engenharia Química, ICEMS, Instituto Superior Técnico, 1049−001 Lisboa, Portugal; and Centro de Física da Matéria Condensada, Universidade de Lisboa, Avenida Professor Gama Pinto 2, 1649-003 Lisboa, Portugal Cite this: Macromolecules 2000, 33, 21, 7675–7678Publication Date (Web):October 3, 2000Publication History Received2 May 2000Revised14 August 2000Published online3 October 2000Published inissue 1 October 2000https://doi.org/10.1021/ma000755qCopyright © 2000 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views197Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (334 KB) Get e-AlertsSUBJECTS:Deformation,Elastomers,Light,Liquid crystals,Stress Get e-Alerts