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Hydrogen bonding between hard segments has a critical effect on the morphology and properties of polyurethanes. Influence of temperature on hydrogen bonded urethane network and melting behavior of a model semicrystalline segmented polyurethane was investigated by experiments and simulations. Polyurethane was synthesized by the stoichiometric reaction between p-phenylene diisocyanate and poly(tetramethylene oxide) (PTMO) with a molecular weight of 1000 g/mol. Simulations were carried out using dissipative particle dynamics (DPD) and molecular dynamics (MD) approaches. Experimental melting behavior obtained by various techniques was compared with simulations. DPD simulations showed a room temperature microphase morphology consisting of a three-dimensional hydrogen-bonded urethane hard segment network in a continuous and amorphous PTMO matrix. The first-order melting transitions of crystalline urethane hard segments observed during the continuous isobaric heating in DPD and MD simulations (340–360 K) were in reasonably good agreement with those observed experimentally, such as AFM (320–340 K), WAXS (330–360 K), and FTIR (320–350 K) measurements. Quantitative verification of the melting of urethane hard segments was demonstrated by sharp discontinuities in energy versus temperature plots obtained by MD simulations due to substantial decrease in the number of hydrogen bonds above 340 K. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017.

A facile synthesis of hydroxyethyl-functionalized poly(ether sulfone) (PESu) oligomers permitted subsequent melt transesterification into segmented block copolymers with poly(butylene terephthalate). The unique solubility of the PESu oligomers in the melt with 1,4-butanediol and dimethyl terephthalate enabled a systematic study of segment length on thermomechanical properties of the resulting block copolymers. 1H NMR spectroscopy revealed a compositional dependence on the average segment length of the PBT. Additionally, the concert of NMR spectroscopy, DSC, and DMA highlighted critical segment lengths for crystallization and phase separation. In agreement with a relatively constant Tm and phase separation observed with DSC and DMA, respectively, small-angle X-ray scattering identified a compositionally independent lamellar thickness, while the amorphous layer thickness increased with PESu incorporation. As a result, the complementary analytical techniques provided an understanding of the morphological inf...

A comprehensive discussion is provided of the critical physical, chemical and structural parameters, such as soft and hard segment structures and their molecular weights, polymer composition, solubility parameters, competitive intermolecular interactions and others, which strongly affect the morphology and bulk and surface properties of segmented thermoplastic polyurethanes, polyureas and polyurethaneureas (TPUs). Important developments related to the design, synthesis and structure-property behavior of segmented polyurethanes are discussed. Although the main emphasis is placed on linear materials, some brief comments are also given on the effect of chemical crosslinking on the structure–property behavior of segmented polyurethanes.

Quantum mechanical calculations (QMC) and dissipative particle dynamics (DPD) simulations were utilized to understand the nature of the short and long-range hydrogen bonding and its influence on the microphase morphology in segmented polyurethanes and segmented polyureas prepared without chain extenders through the stoichiometric reactions of hydroxy or amine terminated poly(tetramethylene oxide) (PTMO-1000) with 1,4-phenylene diisocyanate (PPDI) and 1,3-phenylene diisocyanate (MPDI). The possibility of long-range connectivity due to a network of well-ordered hydrogen bonds between symmetrical PPDI and kinked MPDI based model urethane and urea compounds were also investigated. Special emphasis was given on the understanding of the influence of diisocyanate symmetry and nature of the hydrogen bonding between hard segments on the morphology development. QMC results obtained clearly indicated the possibility of long-range ordering of hydrogen bonds between PPDI based urethane and urea groups, while MPDI based systems did not display such a behavior. DPD results strongly supported the QMC studies and clearly demonstrated the possibility of long-range connectivity of hydrogen bonds between urethane and urea groups in PPDI based segmented copolymers, leading to the formation of microphase separated morphologies in these systems, which was not observed in the kinked MPDI based segmented urethane and urea copolymers. Computational results obtained strongly supported the experimental observations reported on the morphology and thermal and mechanical properties of these segmented polyurethanes and polyureas based on PPDI and MPDI.

Segmented polyurethanes based on polytetramethylene glycol (PTMG) of 1000 g/mol were synthesized using a two-step polymerization procedure. Various hard segments were obtained using hexamethylene diisocyanate (HDI) or 4,4′-methylenebis(phenyl isocyanate) (MDI) as the diisocyanates and hydroquinone bis(2-hydroxyethyl)ether (HQEE) or triptycene-1,4-hydroquinone bis(2-hydroxyethyl)ether (TD) as the chain extenders. The effect of rigidity and bulkiness of the hard segments on morphology, thermal and mechanical properties were studied. Fourier transform infrared (FTIR) suggested that hydrogen bonding interactions were weakened in the presence of the bulky triptycene-containing hard segments. Variable temperature FTIR demonstrated that hydrogen bonds completely dissociate at around 170 °C for polyurethanes chain extended by HQEE compared to around 110 °C for their TD analogs. Polyurethanes from MDI and TD displayed microphase mixing behavior based on atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). When HDI was used as the diisocyanate in the TD chain extended polyurethane, enhanced microphase separation was observed with comparable mechanical properties to those of the MDI analogs with HQEE.

Thermoplastic segmented polyurethanes which are based on poly(tetramethylene oxide) (PTMO) soft segment, linear symmetric para-phenylene diisocyanate (pPDI), and chain extended with 1,4-butanediol (BD) are discussed. The effect of variation of the soft and hard segment molecular weights as well as the overall hard segment content on structure–property behavior is investigated. Together, atomic force microscopy (AFM) and dynamic mechanical analysis (DMA) clearly establish the presence of a unique ordered thread-like microphase separated structure that displays considerable order. This thread-like microphase structure is similar to that of the “single molecule” hard segment systems reported earlier from our laboratory [1] , [2] , [3] , [4] . In addition, small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS) and ambient temperature tensile testing results help to better define the nature of the hard and soft domains.

Micro-phase separation in hexamethylynediisocyanate-polyurea was studied using small-angle X-ray scattering and infrared absorption. It was found that phase separation in this system followed spinodal-like decomposition on a 3–4 nm size scale with phase separation occuring on a time scale of days.

Due to their outstanding mechanical properties and high aspect ratios, carbon nanotubes (CNTs) are envisioned as attractive nanofillers in polymer composites. However, due to strong van der Waals interactions, deleterious aggregation of CNTs is typically observed in polymer nanocomposites. Moreover, due to low stress transfer between the matrix polymer and the nanotube filler, only limited reinforcement is obtained. We report here a novel functionalization strategy to obtain CNTs with pendant self-complementary hydrogen bonding groups in order to address these limitations. Multi-walled CNTs were functionalized with ureidopyrimidinone (UPy) groups, which display multiple hydrogen bonding. The functionalized CNTs were blended with acrylic copolymers containing pendant UPy moieties and significant enhancement in tensile performance of the nanocomposites was observed.

A new triptycene diol (TD), triptycene-1,4-hydroquinone-bis(2-hydroxyethyl) ether, was synthesized and was used to prepare a series of copolyesters with dimethyl 1,4-cyclohexanedicarboxylate (1,4-DMCD) by melt polycondensation. Straight chain aliphatic spacers, including ethylene glycol (EG), 1,4-butanediol (BD), and 1,6-hexanediol (HD), were used as codiols with TD to explore the effects of straight chain flexible spacers on copolyester properties. A concomitant series of non-triptycene copolyesters based on hydroquinone bis(2-hydroxyethyl) ether (HBE), bis[4-(2-hydroxyethoxy)phenyl] sulfone (BHPS), 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane (BHPC), or 1,1-bis(2-hydroxyethoxy)phenyl-3,3,5-trimethylcyclohexane (BHPT) were prepared for comparison. The results demonstrated that the triptycene-containing polyesters in this study have higher thermal stability and higher glass transition temperatures (Tg’s) than the corresponding non-triptycene analogues. For triptycene-containing copolyesters, the mechanic...

Effect of polydimethylsiloxane (PDMS) soft segment molecular weight (Mn = 3200, 10,800 and 31,500 g/mol) and urea hard segment content (2.0–11.4% by weight) on the hysteresis and permanent set behavior of segmented silicone-urea (TPSU) copolymers were investigated. In spite of very low hard segment contents, all copolymers formed self-supporting films and displayed good mechanical properties. When the mechanical hysteresis and set behavior of the silicone-urea copolymers with similar hard segment contents (around 7.5% by weight) but based on PDMS-3K, PDMS-11K and PDMS-32K were compared, it was very clear that as the PDMS molecular weight increased, hysteresis and instantaneous set values decreased significantly. Copolymers based on the same silicone soft segment (PDMS-11K or PDMS-32K) but with different hard segment contents showed a linear increase in hysteresis and a slight decrease in the instantaneous set as a function of hard segment content. Constant initial stress creep experiments also showed lower creep as the PDMS segment molecular weight increased for copolymers with similar urea contents. Since the critical entanglement molecular weight (Me) of PDMS is stated to be 24,500 g/mol, our results tend to suggest important contribution of chain entanglements on the hysteresis and instantaneous set of these silicone-urea copolymers.

We investigated the synthesis and structure–property behaviors of two types of vegetable-oil polyols (soy oil and castor oil) and their use in viscoelastic (VE) polyurethane foams (PUFs). This article is the first in a two-part series. In this initial part, we principally address the dynamic mechanical analysis (DMA) behavior of these foams in conjunction with information on the cellular morphology, sol fraction, and rise and reaction temperature profile behavior (the latter two parameters were determined during the foaming process). Particular emphasis is placed on the DMA damping characteristics, which represent one of the most critical parameters in the application of VE PUFs. It is also shown that the damping characteristics could be modified in such foams by the variation of the isocyanate/hydroxyl (×100) index, the addition of plasticizer, and in the case of soy polyols, the soy content. The frequency dependence of the VE PUFs is also briefly addressed. In the second article in this series, which directly follows this article, we further address the details of other relevant physical properties of these same foams in view of their applied nature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Novel polydimethylsiloxane (PDMS) based polyionenes were synthesized by a modified Menschutkin reaction involving reaction between bromo-terminated PDMS oligomers and various ditertiary amino compounds. In this study, the nature of the hard segment was varied by using various ditertiary amino compounds and in some cases by incorporating chain extenders, while the soft segment content was varied by changing the molecular weight of the PDMS oligomers. The mechanical properties of these materials were found to be dependent on both the nature and amount of the hard segments. These materials also showed distinct evidence of a microphase-separated morphology where under normal conditions, the hard segments formed in what are believed to be cylindrical ion-rich microdomains dispersed randomly in the soft PDMS matrix. When subjected to uniaxial deformation, the ionic cylinders were found to orient along their long axes in the stretch direction.

Novel, segmented thermoplastic silicone–urea (TPSU) copolymers based on rather high molecular weight aminopropyl terminated polydimethylsiloxane (PDMS) soft segments ( 10,800 and 31,500 g/mol), a cycloaliphatic diisocyanate (HMDI) and various diamine chain extenders were synthesized. Copolymers with very low urea hard segment contents of 1.43–14.4% by weight were prepared. In spite of very low hard segment contents, solution cast films showed very good microphase separation and displayed reasonable mechanical properties. Tensile strengths of TPSU copolymers showed a linear dependence on their urea hard segment contents, regardless of the structure of the diamine chain extender used. The modulus of silicone–urea copolymers is dependent on the urea concentration, but not on the extender type or PDMS molecular weight. When silicone–urea copolymers with identical urea hard segment contents were compared, copolymers based on PDMS-31,500 showed higher elongation at break values and ultimate tensile strengths than those based on PDMS-10,800. Since the critical entanglement molecular weight (Me) of PDMS is about 24,500 g/mol, these results suggest there is a significant contribution from soft segment chain entanglement effects in the PDMS-31,500 system regarding the tensile properties and failure mechanisms of the silicone–urea copolymers.

Time-dependent morphology development in segmented polyureas obtained by the stoichiometric reactions between amine terminated poly(tetramethylene oxide) (PTMO) and aromatic diisocyanates were investigated. Polyureas were prepared by reacting aminopropyl terminated PTMO oligomer (Mn = 1100 g/mol) and various aromatic diisocyanates, such as 1,4-phenylene diisocyanate (PPDI), 1,3-phenylene diisocyanate (MPDI), diphenylmethane diisocyanate (MDI), and tolylene diisocyanate (TDI). Time-dependent FTIR studies were conducted on thin films cast onto KBr discs, which were annealed at 200 °C for 10 min in an air oven. After removing from the oven, samples were placed into the FTIR spectrometer at room temperature, where time-dependent spectra were recorded until equilibrium was reached. Time-dependent peak reorganization in 3500–3100 cm−1 (NH region), 1750–1450 cm−1 (CO region or amide I and amide II regions), and 1180–1020 cm−1 (COC) were monitored. Depending on the chemical structure and the symmetry of the diisocyanate, major differences were observed in the time needed to reach an equilibrium morphology in these homologous poly(ether urea) copolymers. Symmetric PPDI-based polyurea reached equilibrium in about 1 h compared with its asymmetric MPDI-based counterpart, which needed about 150 h. Microphase development of the MPDI urea was also characterized by AFM, which gave similar results. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 471–483, 2009

In our previous publication on the structure–property behavior of segmented polyurethanes based on castor oil [Petrovic ZS, Xu Y, Zhang W. Polymer Preprints 2007;48(2):852–3.], the results showed that these materials which possessed a soft segment weight concentration (SSC) of 70% have both low tensile strength and elongation at break. This behavior is distinctly different from segmented polyurethanes of comparable soft segment content obtained from petrochemical polymeric diols that possess terminal hydroxyl groups. The poor elastic properties of these segmented polyurethanes were ascribed to the low molecular weight of the polymers as well as due to the presence of the six-carbon “dangling chain”, which may influence the morphology of the resulting segmented polyurethanes. To further understand this behavior, four segmented polyurethanes with the SSC of 70, 60, 50, and 40%, respectively, were synthesized from a polyricinoleate diol with an Mn of 2580, diphenylmethane diisocyanate (MDI) and butanediol. The objective of this work was to study the effect of SSC on the morphology of the resulting polyurethanes, and to correlate the morphology with the properties of these bio-based segmented polyurethanes. Polymers were characterized by GPC, viscometry and spectroscopic methods. Thermal and mechanical properties of the polymers indicated good microphase separation. Microphase morphology was also noted by SAXS and AFM. Finally, “spherulitic-like” superstructures were noted in the solution cast films that are believed to arise from the nucleation and crystallization of the hard segments.

The effects of long-range connectivity between urea hard domains on the microphase morphology and mechanical properties of novel, segmented, non-chain extended polyureas based on single isocyanate molecules were analyzed. This was achieved by systematic disruption of the intermolecular bidentate hydrogen bonding between the urea hard segments by the incorporation of a hydrogen bond screener, LiCl. A systematic decrease in the breadth of the service temperature window and mechanical properties of the polyureas were observed in the presence of LiCl, due to the disruption of the long range connectivity between the hard segments. The above mentioned effects were also found to be dependent on the symmetry of the diisocyanate hard segments.

Segmented thermoplastic polyurethanes, polyureas and polyurethaneureas (TPU) based on a given hard segment and two chemically different soft segments display interesting microphase morphologies and thermal, mechanical and surface properties. In these systems the final TPU morphology is mainly controlled by the structure, amount and molecular weight of the soft segment oligomers and the nature and extent of specific intermolecular interactions between the mixed soft segments themselves and with the urethane hard segments. These interactions lead to variable compatibilities between the soft and hard segments resulting in interesting TPU morphologies. The proper choice of the two chemically different soft blocks provides more flexibility in controlling the extent of microphase separation, size and shape of the microphase domains and offers new possibilities for controlling the properties of TPUs. In this study coarse grained computer simulations were carried out to better understand the nature of intermolecular interactions and to elucidate the equilibrium microphase morphologies of TPUs with two different soft segments at 300 K. Model TPU systems investigated are comprised of poly(tetramethylene oxide) (PTMO) or poly(hexylethyl carbonate) (PHEC) and polydimethylsiloxane (PDMS) or polyisobutylene (PIB) soft segments with molecular weights in the range of 500-2500 g/mol. Hard segments consisted, in all cases, of diphenylmethane diisocyanate (MDI) based urethane repeat units and ranged from 25 to 50% by weight. Through coarse grained Dissipative Particle Dynamics (DPD) simulations it was demonstrated that by varying the composition and the chain lengths of the soft and hard blocks, quite different morphologies from homogeneous (or mixed) to gradient and to completely microphase separated structures were attainable. As expected, fairly hydrophobic soft blocks such as PIB and PDMS favored strong microphase separation when compared with relatively hydrophilic PHEC and PTMO segments. For comparison, morphologies of the TPUs based on single soft segments (PTMO, PHEC, PDMS and PEO) with varying molecular weights and hard segment contents were also simulated. (C) 2016 Elsevier Ltd. All rights reserved.

Segmented, nonchain extended polyurethanes and polyureas based on PTMO soft segments (SS) and hard segments (HSs) based on only single molecules of a diisocyanate were synthesized. Type and nature of the diisocyanate was systematically varied in order to analyze the effect of HS symmetry and type of linkage between the HS and SS on the structure‐property relationship of these segmented copolymers. Results showed that the increased symmetry of the diisocyanates allows a more efficient packing of the HSs which leads to a microphase‐separated structure with the crystalline hard ribbon or thread‐like domains percolated throughout the SS matrix, even with a low HS content (ca. 13 wt.%). The service window of these segmented copolymers was significantly influenced by the symmetry and type of linkage between the HS and SS. Most copolymers also showed evidence of strain hardening accented by the strain induced crystallization of the PTMO SS.

Raw soybean oil was hydroxylated with acetic acid and hydrogen peroxide to prepare soy-based polyols of various functionalities. These polyols were reacted with a modified diphenyl methane diisocyanate (Isonate 143L) to make polyurethane networks. The sol fractions decreased as the hydroxyl number of the polyol increased, and the glass-transition temperatures increased with the hydroxyl number, as did the rubbery plateau storage modulus and Young's modulus of the networks. When the glass-transition temperatures of each network were plotted as a function of the polyol's hydroxyl number, a linear relationship was observed over the range investigated. This trend closely matched that of our previous work with soy-based polyurethane networks. A second series of networks was prepared with the same polyols but with different isocyanates. The nature of the crosslinker was shown to somewhat influence the sol fractions, glass-transition temperatures, and stress–strain behavior of the networks. A linear relationship was recorded between the storage modulus at 125°C of a network and the average functionality of the polyol from which it was synthesized. Finally, two separate polyurethane networks were prepared through the blending of two polyols: one based on petroleum and the other based on soy. These networks were also characterized, and the compatibility of each blend was addressed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Novel, segmented non-chain extended polyureas were synthesized. Soft segments (SS) were based on poly(tetramethylene glycol) (PTMO) (average molecular weight 1000 or 2000 g/mol) and hard segments (HS) were based on a single molecule of a diisocyanate, which was either 1,6-hexamethylene diisocyanate (HDI), 1,4-phenylene diisocyanate (pPDI) or 1,4-trans-cyclohexyl diisocyanate (CHDI). An increase in the SS molecular weight was found to lead to an increased formation of SS crystallites below 0 °C, which increased the low temperature modulus. Both 1K and 2K PTMO-based polyureas showed a microphase separated morphology, where the HS formed thread-like, crystalline structures that were dispersed in the continuous SS matrix. Upon deformation, the HS were found to breakdown into distinctly smaller threads, which oriented along the direction of the strain; this effect was found to be partially reversible and time dependent. Both the 1K and 2K polyureas based on HDI HS were found to be thermally stable and potentially melt-processible.

Ionomeric polymer transducers (sometimes called “ionic polymer–metal composites,” or “IPMCs”) are a class of electroactive polymers that are able to operate as distributed electromechanical actuators and sensors. Traditionally, these transducers have been fabricated using water-swollen Nafion membranes. This work seeks to overcome the hydration dependence of these transducers by replacing water with an ionic liquid. In the current work, two ionic liquids are studied as diluents for ionomeric polymer transducers based on Nafion membranes. The two ionic liquids used are 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-Im). These two ionic liquids were chosen for their low viscosity and high conductivity. Furthermore, although many of the physical properties of the two ionic liquids are similar, the EMI-Tf ionic liquid is water miscible whereas the EMI-Im ionic liquid is hydrophobic. These important similarities and differences facilitated investigations of the interactions between the ionic liquids and the Nafion polymer. This paper examines the mechanisms of electromechanical transduction in ionic liquid-swollen transducers based on Nafion polymer membranes. Specifically, the morphology and relevant ion associations within these membranes are investigated by the use of small-angle X-ray scattering (SAXS), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. These results reveal that the ionic liquid interacts with the membrane in much the same way that water does, and that the counterions of the Nafion polymer are the primary charge carriers in the ionic liquid-swollen films. The results of these analyses are compared to the macroscopic transduction behavior in order to develop a molecular/morphological model of the charge transport mechanism responsible for electromechanical coupling in these membranes.

Novel segmented polyurethanes with hard segments based on a single diisocyanate molecule with no chain extenders were prepared by the stoichiometric reactions of poly(tetramethylene oxide)glycol ( M n =1000 g/mol) (PTMO-1000) and 1,4-phenylene diisocyanate (PPDI), trans -1,4-cyclohexyl diisocyanate (CHDI), bis(4-isocyanatocyclohexyl)methane (HMDI) and bis(4-isocyanatophenyl)methane (MDI). Time dependent microphase separation and morphology development in these polyurethanes were studied at room temperature using transmission FTIR spectroscopy. Solvent cast films on KBr discs were annealed at 100 °C for 15 s and microphase separation due to self organization of urethane hard segments was followed by FTIR spectroscopy, monitoring the change in the relative intensities of free and hydrogen-bonded carbonyl (C O) peaks. Depending on the structure of the diisocyanate used, while the intensity of free C O peaks around 1720–1730 cm −1 decreased, the intensity of H-bonded C O peaks around 1670–1690 cm −1 , which were not present in the original samples, increased with time and reached saturation in periods ranging up to 5 days. Structure of the diisocyanate had a dramatic effect on the kinetics of the process and the amount of hard segment phase separation. While PPDI and CHDI based polyurethanes showed self-organization and formation of well ordered hard segments, interestingly no change in the carbonyl region or no phase separation was observed for MDI and HMDI based polyurethanes. Quantitative information regarding the relative amounts of non-hydrogen bonded, loosely hydrogen bonded and strongly hydrogen bonded and ordered urethane hard segments were obtained by the deconvolution of C O region and analysis of the relative absorbances in C O region.

The effect of time and temperature on the air oxidation of soybean oil in the absence of catalysts or added initiators was investigated. It was possible to divide the air oxidation of soybean oil into three regimes. The first regime of air oxidation resulted in insignificant change in the hydroxyl number. During this regime, it was proposed that natural antioxidants, which are present in raw soybean oil, were consumed and peroxide formation occurred. A drastic increase in hydroxyl number due to the formation and subsequent decomposition of peroxides marked the second regime of air oxidation. In the third regime of air oxidation, free radical crosslinking of the soybean oil occurred, and an insoluble gel was formed. The three regimes of air oxidation were used as a guide for the preparation of soy-based polyols and crosslinked polymers. Crosslinked, tack-free coatings were prepared from a metal catalyzed oxidation of soybean oil, where soybean oil and ambient oxygen were the only reactants. Higher temperatures (125°C) were more efficient than lower (50°C) for obtaining high gel fractions and tack-free coatings. Cure of the coatings was expedited with exposure of the coating to UV irradiation after initial heating. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 690–697, 2006

Polyurethane Networks (PUNs) were synthesized using polyols derived from soybean oil, petroleum, or a blend of the two in conjunction with diisocyanate. The soybean-based polyols (SBPs) were prepared using air oxidation, or by hydroxylating epoxidized soybean oil. Some of the networks were subjected to several solvents to determine their respective swelling behavior and solubility parameters. Sol-fractions were also determined, and DMA experiments were utilized to monitor the changes in storage modulus and tan δ with temperature for networks with sol and with the sol extracted. A linear relationship was noted between the hydroxyl number of a SBP and the glass transition temperature of its corresponding unextracted PU network within the range of hydroxyl numbers (i.e., 55–237 mg KOH/g) and glass transition temperatures (i.e., −21–+83°C) encountered in this work. This same linear relationship was realized between the weighted hydroxyl number of soy and petroleum-based polyol blends and the glass transition temperature of the resulting unextracted and extracted network PUs within the ranges utilized in this study (i.e., 44–57 mg KOH/g, −54–19°C). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1432–1443, 2006

New novel segmented polyurethane and polyurea copolymers have been synthesized without chain extenders and the structure-property behavior of these systems has been investigated. It is shown that by the proper choice of diisocyanate and its symmetry, one can obtain highly microphase separated systems without chain extenders and that the materials also display useful mechanical behavior. In particular, it is shown that due to the bidentate hydrogen bonding achieved in the segmented ureas, a significant modulus “service temperature window” is also obtained. It is also verified that not only can strong microphase separation be obtained with low weight fraction hard segment content (14%) but that the hard phase, which is comprised of monodisperse “single molecule” units, also displays a percolated thread-like structure throughout the dominant soft segment material — the latter being based on ca. 1000g/mol polytetramethylene oxide.

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.

The solid-state structure–property behavior of highly branched segmented poly(urethane urea) (PUU) copolymers and their linear analog was investigated. A limited study of their solution rheological behavior was also undertaken. The linear PUUs were synthesized by the two-step prepolymer method, whereas the oligomeric A2+B3 methodology was utilized to synthesize the highly branched materials. The soft segments (SS) were either poly(tetramethylene oxide) (PTMO) or poly(propylene oxide) (PPO). All copolymers utilized in this study, with one exception, contained 28 wt% hard segment (HS) content. DMA, SAXS, and AFM studies indicated that the linear as well as the highly branched PUUs were microphase separated. The SS Tg of the highly branched PUUs was nearly identical to that of their respective linear analogs. However, the linear copolymers exhibited broader and less temperature sensitive rubbery plateaus, both attributed to one or both of two reasons. The first is better hydrogen bonding organization of the HS phase as well as greater HS lengths than in the highly branched analogs. The second parameter is that of a potentially higher chain entanglement for the linear systems relative to the branched analogs. Tapping-mode AFM phase images confirmed the microphase morphology indicated by SAXS and DMA. Ambient temperature strain-induced crystallization was observed in the PUU based on PTMO 2040 g/mol at a uniaxial strain of ca. 400%, irrespective of the chain architecture. Stress–strain, stress relaxation, and mechanical hysteresis of the highly branched copolymers were in general slightly poorer than that of their linear analogs. Ambient temperature solution viscosity of the highly branched materials in dimethyl formamide was substantially lower that that of the linear samples of nearly equal molecular weight.

The time-dependent morphology development in a segmented polyurethane, which was prepared by the reaction of equimolar amounts of 1,4-phenylene diisocyanate (pPDI) and poly(tetramethylene oxide)glycol of 〈Mn〉 of 975 g/mol, was investigated. No chain extender was utilized during the synthesis, and the resultant monodisperse hard segments constituted 14 wt % of the copolymer. Time-dependent microphase separation and morphology development was studied at room temperature by using solvent-cast films which were heated above the hard segment melting temperature, 55 °C, to erase the semicrystalline microphase morphology. Atomic force microscopy showed that, following heat treatment, the hard phase first developed into short rods within 30 min, followed by a growth period during which the short rods grew longer and eventually into a well-defined percolated structure. Morphology development was also followed by FTIR spectroscopy. While the intensity of the free CO peak at 1730 cm-1 decreased, the intensity of the ...

Poly(propylene oxide) (PPO) was incorporated in a controlled manner between poly(dimethylsiloxane) (PDMS) and urea segments in segmented polyurea copolymers and their solid state structure–property behavior was investigated. The copolymers contained PDMS segments of MW 3200 or 7000 g/mol and an overall hard segment content of 10–35 wt%. PPO segments of MW 450 or 2000 g/mol were utilized. Equivalent polyurea copolymers based on only PDMS as the soft segment (SS) component were used as controls. The materials (with or without PPO) utilized in this study were able to develop microphase morphology as determined from dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). DMA and SAXS results suggested that the ability of the PPO segments to hydrogen bond with the urea segments results in a limited inter-segmental mixing which leads to the formation of a gradient interphase, especially in the PPO-2000 co-SS containing copolymers. DMA also demonstrated that the polyureas based on only PDMS as the SS possessed remarkably broad and nearly temperature insensitive rubbery plateaus that extended up to ca. 175 °C, the upper temperature limit depending upon the PDMS MW. However, the incorporation of PPO resulted in more temperature sensitive rubbery plateaus. A distinct improvement in the Young's modulus, tensile strength, and elongation at break in the PPO-2000 and PDMS-7000 containing copolymers was observed due to inter-segmental hydrogen bonding and the formation of a gradient interphase. However, when PPO was incorporated as the co-SS, the extent of stress relaxation and mechanical hysteresis of the copolymers increased relative to the segmented polyureas based on the utilization of only PDMS as the soft segment component.

Three nearly identical linear low density polyethylene resins based on copolymers of ethylene with 1-butene (B), 1-hexene (H) and 1-octene (O) were utilized to investigate the effect of short chain branch length on the mechanical properties of blown and compression molded (quenched and slow cooled) films. The content of short chain comononer in the three copolymers was ca. 2.5–2.9 mol% that corresponded to a density of 0.917–0.918 g/cm 3 . Within a given series, the tensile properties of these films do not show any significant difference at slow deformation rates (up to 510 mm/min), even though the DSC and TREF profiles of ‘H’ and ‘O’ differed slightly in comparison to ‘B’. However, at higher deformation rates (ca. 1 m/s), the breaking strength of these films was found to increase with increasing short chain branch length. In addition, the Spencer impact and Elmendorf tear strength of the blown films were also observed to increase with increasing short chain branch length. Further, dart impact strength and high-speed puncture resistance (5.1 m/s) of 1-octene and 1-hexene based samples was also observed to be higher than that based on 1-butene. The blown films displayed low and comparable levels of equivalent in-plane birefringence and crystalline orientation by wide angle X-ray scattering. This confirms that the differences in mechanical properties in the blown film series are not attributable to differences in molecular orientation. The deformation behavior of both the compression molded and blown films were also investigated in a well-defined controlled regime by analyzing their essential work of fracture. It was found that the essential work of fracture of films based on 1-hexene and 1-octene was higher than that of films based on 1-butene. While the origin of these differences in mechanical properties with increasing short chain branch length is not fully understood, the present investigation confirms this effect to be pronounced at high deformation rates for both the blown and compression molded quenched films.

Thermoplastic segmented polyurethane and polyurea copolymers whose monodisperse hard segments are based on only a single diisocyanate molecule are discussed. The solid-state structure-property behavior of these materials demonstrates that a proper selection of the level of symmetry and/or cohesiveness of the hard microdomains may allow elimination of the traditional requirement of chain extension to obtain melt processable segmented urethanes, and more specifically, urea copolymers with useful structural properties.

Many polyurethane elastomers display excellent mechanical properties and adequate biocompatibility. However, many medical-grade polyurethanes are prepared from aromatic diisocyanates and can degrade in vivo to carcinogenic aromatic diamines, although the question of whether the concentrations of these harmful degradation products attain physiologically relevant levels is currently unresolved and strongly debated. It is therefore desirable to synthesize new medical-grade polyurethanes from less toxic aliphatic diisocyanates. In this paper, biocompatible segmented polyurethane elastomers were synthesized from aliphatic diisocyanates (1,4-diisocyanatobutane (BDI) and lysine methyl ester diisocyanate (LDI)), novel diurea diol chain extenders based on tyrosine and tyramine, and a model poly(ethylene glycol) (PEG) diol soft segment. The objectives were to design a hard segment similar in structure to that of MDI-based polyurethanes and also investigate the effects of systematic changes in structure on mechanical and biological properties. The non-branched, symmetric polyurethane prepared from BDI and a tyramine-based chain extender had the highest modulus at 37 degrees C. Introduction of symmetric short-chain branches (SCBs) incorporated in the tyrosine-based chain extender lowered the modulus by an order of magnitude. Polyurethanes prepared from LDI were soft polymers that had a still lower modulus due to the asymmetric SCBs that hindered hard segment packing. Polyurethanes prepared from tyramine and tyrosine chain extenders thermally degraded at temperatures ranging from 110 to 150 degrees C, which are lower than that reported previously for phenyl urethanes. All four polyurethanes supported the attachment, proliferation, and high viability of MG-63 human osteoblast-like cells in vitro. Therefore, the non-cytotoxic chemistry of these polyurethanes make them good candidates for further development as biomedical implants.

A series of seven linear homopolymers of poly(methylmethacrylate) ranging from 12,470 to 365,700 g/mol M w , were utilized to further explore scaling relationships between viscosity and concentration in a good solvent at 25 °C and to investigate the impact of these relationships on fiber formation during electrospinning. For each of the polymers investigated, chain dimensions (hydrodynamic radius and radius of gyration) were measured by dynamic light scattering to determine the critical chain overlap concentration, c * . The experimentally determined c * , was found to be in good agreement with the theoretically determined value that was calculated by the criteria c * ∼1/[ η ], where the intrinsic viscosity was estimated from the Mark–Houwink parameters, K and a (at 25 °C in dimethyl formamide) obtained from the literature. The plot of the zero shear viscosity vs. c / c * distinctly separated into different solution regimes, viz. dilute ( c / c * c / c * c / c * >3). The crossover between semidilute unentangled and semidilute entangled regimes in the present investigation occurred at c / c * ∼3, which, therefore, marked the onset of the critical chain entanglement concentration, c e , according to the procedure utilized by Colby and co-workers [Colby RH, Rubinstein M, Daoud M. J de Phys II 1994;4(8):1299–310. [52] ]. Electrospinning of all solutions was carried out at identical conditions to ascertain the effects of solution concentration, molecular weight, molecular weight distribution and viscosity on fiber formation and morphological features of the electrospun material. Only polymer droplets were observed to form from electrospinning of solutions in the dilute concentration regime due to insufficient chain overlap. As the concentration was increased, droplets and beaded fibers were observed in the semidilute unentangled regime; and beaded as well as uniform fibers were observed in the semidilute entangled regime. Uniform fiber formation was observed at c / c * ∼6 for all the narrow MWD polymers ( M w of 12,470–205,800 g/mol) but for the relatively broad MWD polymers ( M w of 34,070 and 95,800 g/mol), uniform fibers were not formed until higher concentrations, c / c * ∼10, were utilized. Dependence of fiber diameter on concentration and viscosity was also determined, viz. fiber dia∼( c / c * ) 3.1 and fiber dia ∼ η 0 0.71 respectively. These scaling relationships were in general agreement with that observed by Mckee et al. [McKee MG, Wilkes GL, Colby RH, Long TE. Macromolecules 2004;37(5):1760–67. [33] ].

Soluble model segmented poly(urethane urea)s (PUU) with or without hard segment (HS) branching were utilized to explore the importance of hydrogen bonding and chain architecture in mediating the long-range connectivity of the HS phase. The HS content of all the PUU copolymers was 22 wt %, and the soft segment (MW 970 g/mol) was a heterofed random copolymer of 50:50 ethylene oxide:propylene oxide, which possesses a single terminal hydroxyl group (monol). An 80:20 isomeric mixture of 2,4- and 2,6-toluene diisocyanate, 4,4',4''-triphenylmethane triisocyanate and water were utilized during the chain extension step of the synthesis to incorporate HS branching. DSC and SAXS results on the final plaques indicated that the samples were still able to establish a microphase morphology even in the presence of the highest extent of HS branching utilized in the study. The tapping-mode AFM phase image of the PUU sample without HS branching exhibited the presence of long ribbonlike hard domains that percolated through the soft matrix. The long-range connectivity of the HS was increasingly disrupted with higher levels of HS branching. Accompanying such disruption was a systematic mechanical softening of the PUU samples. FT-IR indicated that incorporation of HS branching disrupted the hydrogen-bonded network within the hard phase. These results demonstrate the importance of hydrogen bonding and chain architecture in mediating the long-range connectivity and percolation of the HS and achieving dimensional stability.

A series of methacrylated poly(propylene oxide)/reduced styrene content/dimethacrylate resin systems have been prepared. These modified vinyl esters may be ideal for coatings, toughened matrix resins for fiber-reinforced composites, bridge deck wear surface resins, and structural adhesive applications. Network systems cured with room-temperature and elevated-temperature cure methods have been studied. The network morphologies were investigated by DMA and TEM analyses. The K1c values of the adhesives increases when systems were cured with the room-temperature cure package. The lap-shear strength of these systems were investigated for structures including composite-to-composite, composite-to-steel, and composite-to-concrete following ASTM D1002. Lap-shear adhesive strengths of all of the adhesives, which had appropriate viscosities on composite substrates, were in the structural regime with values of ∼13.8 MPa. Room-temperature cure schedules (with and without a postcure) resulted in good adhesive ...

Electrical charging and residual charge decay of electro-spun nonwoven webs comprised of two electrically dissimilar polymers were studied in an effort to investigate their filtration properties. Polystyrene (PS) and polyacrylonitrile (PAN) were electrospun separately, in a layer-by-layer configuration and simultaneously in a side-by-side bi-component apparatus into thin webs on a polypropylene spunbond substrate. During electrospinning of the PS and PAN polymer solutions, the fibers became positively charged when positive voltage was applied to the solution-filled spinning nozzle and became negatively charged when negative voltage was applied. This study was undertaken to examine the effect of cooperative charging from electrospinning of the two polymers, the effect of the three types of web constructions on charge retention, and filtration properties of the fibers. It was found that single, multilayered, and bi-component webs retained surface charges in the thousands of volts that diminished very little over a 20-hour period, but eventually bled off while resting for three months. Filtration properties were found to be exceptionally high for some, but not all, electrospun samples; filtration was found to have a weak dependence on both surface charge and web geometrical factors, particularly the fiber diameter, that influence pressure drop of the aerosol test.

A novel methodology for in situ cross-linking of polymeric fibers during electrospinning is described. The electrospinning apparatus was modified to facilitate UV irradiation of the electrospun fibers while in flight to the collector target. Three polymers with different mol % of the photoreactive cinnamate functional group (4, 9, and 13 mol %) were synthesized and utilized for this study. Fibers of cinnamate functionalized poly(methyl methacrylate-co-2-hydroxyethyl acrylate) were cross-linked in situ by UV irradiation during electrospinning. Subsequent FTIR measurements on irradiated and nonirradiated electrospun fibers indicated both [2π + 2π] cycloaddition of the vinylene CC and trans−cis photoisomerization of the cinnamate group. Furthermore, the irradiated copolymers were observed to form insoluble gels which indicated that the photodimerization was the primary photoprocess during UV irradiation, leading to the formation of a cross-linked network. As expected, it was found that the gel fraction incre...

The effect of the variables of polydimethylsiloxane (PDMS) soft segment (SS) length, hard segment (HS) type and content as well as choice of chain extender (its MW and symmetry) on the morphology of segmented polyurethane and polyurea copolymers was investigated. The methods of dynamic mechanic analysis, small angle X-ray scattering, atomic force microscopy, and mechanical testing were used in this analysis. Average PDMS MW of 900, 2500 or 7000 g/mol were utilized and the hard segment content ranged from 16 to 50 wt%. HMDI was used as the diisocyanate. All copolymers were synthesized via the prepolymer method. The PDMS MW had a marked effect on the morphology of the materials. Copolymers with PDMS MW of 2500 and 7000 g/mol were clearly found to be well microphase separated relative to those containing the 900 g/mol PDMS SS. The polyurea sample with a PDMS MW of 7000 and HS content of 25 wt% exhibited a remarkable service temperature window (for rubber-like behavior) of ca. 230 °C (from −55 to 175 °C) whereas it was ca. 200 °C wide (from −55 to 145 °C) for the equivalent polyurethane sample. In general, the degree of microphase separation was found to be greater in the polyurea samples due to their more cohesive bidentate hydrogen bonding.

The influence of the extent of hydrogen bonding in mediating the long-range connectivity and percolation of the hard segment phase in model tri-segment oligomeric polyurethanes (PU) was explored by using LiCl as a molecular probe. A 22 wt% hard segment containing model PU plaque based on a mono-functional oligomeric polyether, 80:20 2,4:2,6 isomeric mixture of toluene diisocyanate, and water as a chain extender was employed. Samples cast from 20 wt% solutions in dimethyl acetamide were utilized. The tapping-mode atomic force microscopy (AFM) phase image of the solution cast film sample (soft segment Tg −63 °C) without LiCl exhibited the presence of long interconnected ribbon-like hard domains. The long-range connectivity and percolation of the hard phase that arose during plaque formation gave rise to a brittle rigid solid. A systematic break-up of the hard domains was also observed by AFM when the concentration of LiCl was increased from 0.1 to 1.5 wt%. DSC analysis indicated that the samples were able, however, to maintain a microphase separated morphology even at the highest LiCl concentration utilized in the study. FT-IR data confirmed that LiCl interacts with the hard domains of the model PU samples by disrupting the hydrogen bonding capability of the urea hard segments. A systematic softening of the samples was observed with increasing LiCl content as confirmed by thermomechanical analysis. Thus, this study indicates that hydrogen bonding plays an important role in assisting the hard segments in PU to develop long-range connectivity and percolation of this phase through the soft matrix.

Low molecular weight model trisegmented polyurethanes based on monofunctional polyols, or ‘monols’, with water-extended toluene diisocyanate (TDI) based hard segments (HS) are investigated. The formulations of the materials generated are similar to those of flexible polyurethane foams with the exceptions that the conventional polyol is substituted by an oligomeric monofunctional polyether of ca. 1000 g/mol molecular weight; and no surfactant is utilized. Plaques formed from these model systems are shown to be solid materials at ambient even at their relatively low molecular weights of 3000 g/mol and less. SAXS, DSC, and AFM are utilized to investigate the microphase separated morphologies of the samples generated. WAXS results show that the local packing of the HS is of a similar nature as that in actual flexible polyurethane foams. AFM phase images, for the first time, reveal the ability of the HS to self-assemble through bidentate hydrogen bonding and form lath-like percolated structures, resulting in solid plaques, even though the overall volume of the system is well dominated by the two terminal liquid-like polyether segments.

Epoxidized soybean oil was effectively converted to carbonated soybean oil (CSBO) containing five-membered cyclic carbonates by reaction with carbon dioxide in the presence of tetrabutylammonium bromide as catalyst at 110°C in high yield. CSBO could easily react with di- or tri- primary amines to give the corresponding nonisocyanate polyurethane networks (NIPUs). A model reaction between CSBO and n-butylamine showed the effective ring opening of five-membered cyclic carbonate moieties in the triglyceride molecules by the amine to form β-hydroxyurethane systems. NIPUs were further characterized by the three techniques of solvent extraction, dynamical mechanical analysis, and limited tensile testing. The data from these methods confirmed the network character of all materials and also showed how the levels of extractables, Tg, and mechanical properties varied with type of amine and, in the case of ethylenediamine, the effect of stoichiometry. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 883–891, 2004

Approximately 30 years after their preparation, the nanoscale morphology of a series of ‘model’ segmented polyurethane elastomers has been further elucidated using the technique of tapping mode AFM. The materials investigated are based on 1,4-butanediol extended piperazine based hard segments and employ poly(tetramethylene oxide) soft segments. The chemistry of these polyurethanes was specifically controlled in a manner which yielded monodisperse hard segments precisely containing either one, two, three, or four repeating units. Phase images obtained via AFM, for the first time, enable visual representation of the microphase separated morphology of these materials. AFM images also confirmed the presence of a spherulitic morphology, as shown several years ago using SALS and SEM. In addition, applying AFM to films of freshly prepared solution cast samples, the observed lath-like hard domains are suggested to preferentially orient with their long axis along the radial direction of the spherulites, while the respective crystalline hard segments comprising the hard domains are, in turn, preferentially oriented perpendicular to the spherulitic radius. The hard domain connectivity was found to increase with increasing percentage hard segment content of the polymers.

Simultaneous electrospinning of two polymer solutions in a side-by-side fashion is conducted for two bicomponent polymer systems—poly (vinyl chloride)/segmented polyurethane (PVC/Estane®) and poly(vinyl chloride)/poly(vinylidiene fluoride) (PVC/PVDF). The new experimental device is described and suitable process conditions to electrospin bicomponent fibers are described. Field emission scanning electron microscopy and energy dispersive spectroscopy were utilized to interpret the results regarding local structure and chemical composition, respectively.

Recent advances in the catalyst technology associated with the production of poly(propylene glycol) (PPG) have allowed for the fabrication of ultralow monol content PPG macrodiols (Acclaim™ polyols), which are highly bifunctional and can be produced in substantially higher molecular weights and with narrower molecular weight distributions than previously possible. These factors have enabled the preparation of higher value elastomers and may allow for the first manufacture of economically attractive PPG-based poly(urethane-urea) (PUU) fibers. In the past, many performance polyurethane and PUU elastomers used poly(tetramethylene ether glycol) (PTMEG) for the soft segments either alone or in combination with other macrodiols. The work presented here details the investigation of the morphological features of PUU systems with mixed soft segments of PPG, PTMEG, and a low molecular analog of PPG, tri(propylene glycol) (TPG) in an effort to ascertain the influence of structural features on the mechanical and thermal properties of the elastomers. Also of interest was whether the incorporation of PPG and TPG would either prohibit or greatly hinder the formation of strain-induced PTMEG crystallites. It was found that, even when only 60 wt % of the soft segments consisted of PTMEG, those soft segments were still able to undergo recognizable strain-induced crystallization as detected by wide-angle X-ray scattering. It was also seen that, as the ratio of PPG to PTMEG was varied, there were systematic changes in the soft segment glass transition and cold crystallization characteristics. Inclusion of PPG and TPG resulted in PTMEG's diminished ability to undergo cold and strain-induced crystallization, as seen with differential scanning calorimetry and wide-angle X-ray scattering. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3520–3529, 2003

The effects of methyl acrylate (MA) incorporation (0–15 mol%) on the glass transition, melting behavior, and the peak temperature of the stabilization exotherm in acrylonitrile (AN) based copolymers were studied. A qualitative decrease in crystalline content with increasing MA content was observed using wide angle X-ray scattering (WAXS). The lower crystallinity of the high MA content copolymers could also be noted by the magnitudes of the modulus drop at Tg using dynamic mechanical analysis (DMA) and the step change in heat capacity at Tg using differential scanning calorimetry (DSC). The DSC and differential thermal analysis (DTA) results indicated that the melting temperature of the copolymers decreased with increasing MA content. The magnitude of the crystallization exotherms decreased with successive melting/crystallization cycles. DTA experiments demonstrated that the stabilization reaction, which transforms polyacyrlonitrile into an insoluble, rigid structure, is delayed by the presence of the comonomer.

Lithium bromide (LiBr) was incorporated in formulations based on molded flexible polyurethane foams in order to alter systematically the phase separation behavior and thus give insight into urea phase connectivity. The formulations of the materials generated were similar to those of molded flexible polyurethane foams except that a surfactant and a low molecular weight cross-linking agent (such as diethanol amine) were not used. The resulting materials were evaluated by using the techniques of atomic force microscopy (AFM), SAXS, and DSC. Atomic force microscopy and SAXS were used to demonstrate that the materials with and without LiBr were microphase separated and possessed average interdomain spacings of ca. 90 A, typical of flexible polyurethane foams. AFM phase images also showed that incorporation of LiBr reduced the urea phase aggregation, which is known to take place in flexible polyurethane foams, and led to a more homogeneous distribution of the urea microdomains in the soft polyol phase....