Polyisobutylene‐based polyurethanes. II. Polyureas containing mixed PIB/PTMO soft segments

The design, synthesis, characterization, and structure–property behavior of polyureas containing novel soft segments of mixed polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) chains and conventional hard segments is presented. Modest amounts (12%) of PTMO in the soft PIB phase significantly increase both the tensile strength and elongation of the polyureas. These polyureas exhibit not only oxidative/hydrolytic stabilities far superior to Bionate® and Elast‐Eon® considered the most oxidatively stable polyurethanes on the market but also display mechanical properties (29 MPa tensile strength and 200% elongation) approaching those of conventional thermoplastic polyurethanes. The surfaces of these polyureas are covered/protected by PIB segments, which will lead to excellent biocompatibility. Our results demonstrate that the PTMO segments facilitate stress transfer from the continuous mixed soft phase to the dispersed hard phase, which strengthens and flexibilizes PIB‐based polyureas and thus significantly improves elastomeric properties without compromising oxidative and hydrolytic stability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2787–2797, 2009     

PIB‐based polyurethanes. IV. The morphology of polyurethanes containing soft co‐segments*

Novel polyurethanes consisting of polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) or PIB/poly(hexamethylene carbonate) (PC) soft co‐segments in combination with 4,4′‐methylene‐bis(cyclohexyl isocyanate)/1,6‐hexanediol, 1,4‐butanediol, or 1,6‐hexamethylene diamine hard segments exhibit excellent mechanical properties (upto 31 MPa tensile strength with 700% elongation) together with unprecedented oxidative/hydrolytic stability. A structural model of the morphology of these polyurethanes was developed that reflects this combination of properties. The key new elements of our model are H bridges between the PTMO and PC type soft and urethane hard segments, which compatibilize the soft and hard domains, and the presence of large quantities of chemically resistant PIB soft segments that protect the other oxidatively/hydrolytically vulnerable constituents. A variety of FTIR, DSC, SAXS, AFM, and DMTA experiments strongly support the proposed morphological model. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6180–6190, 2009     

Polyisobutylene‐based polyurethanes. V. Oxidative‐hydrolytic stability and biocompatibility

The oxidative/hydrolytic stability of polyurethanes (PUs) containing exclusively polyisobutylene (PIB), or mixed PIB/polytetramethylene oxide (PTMO), or mixed PIB/polyhexamethylene carbonate (PC) soft segments was investigated. The tensile strengths and elongations of various PUs were determined before and after agitating in 35% HNO₃ or 20% H₂O₂/0.1 M CoCl₂ solutions and retentions were quantified. The presence of PIB imparts significant oxidative/hydrolytic resistance. The tensile strength and elongation of PUs containing 70% PIB, or those of mixed PIB/PC soft segments with 50% PIB, remained essentially unchanged upon exposure to HNO₃; in contrast, PUs containing mixed PIB/PTMO soft segments with 50% PIB underwent significant degradation. The tensile strength of PUs with mixed PIB/PC (60/10%) soft segment increased after exposure to HNO₃, most likely because of oxidative crosslinking of PC segments. PIB/PTMO‐ and PIB/PC‐based PUs and commercially available PUs (Elast‐Eon® and Carbothane®) were exposed to H₂O₂/CoCl₂ solutions for up to 14 weeks. Although the experimental PIB/PC‐based PUs exhibited negligible change in mechanical properties and no surface damage, Elast‐Eon® and Carbothane® showed significant surface damage. PIB‐based polyureas and Bionate® were implanted in rats for 4 weeks in vivo, and their biocompatibility was investigated. The biocompatibility of PIB‐based materials was superior to Bionate®. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2194–2203, 2010     

Polyisobutylene‐based segmented polyureas. I. Synthesis of hydrolytically and oxidatively stable polyureas

Novel segmented polyurea elastomers containing soft polyisobutylene (PIB) segments were synthesized and characterized. The key ingredient, primary amine‐telechelic PIB oligomers (NH₂‐PIB‐NH₂) with number average molecular weights of 2500 and 6200 g/mol were synthesized. PIB‐based polyureas were prepared by using various aliphatic diisocyanates and diamine chain extenders with hard segment contents between 9.5 and 46.5% by weight. All copolymers displayed microphase morphologies as determined by dynamic mechanical analysis. Tensile strengths of nonchain‐extended and chain‐extended polyureas showed a linear dependence on the urea hard segment content. PIB‐based polyureas prepared with NH₂‐PIB‐NH₂ of M_n = 2500 g/mol, 4,4′‐methylendbis(cyclohexylisocyantate), and 1,6‐diaminohexane containing 45% hard segment exhibited 19.5 MPa tensile strength which rose to 23 MPa upon annealing at 150 °C for 12 h. With increasing hard segment content, elongation at break decreased from ～ 450% to a plateau of 110%. The hydrolytic and oxidative stability of PIB‐based polyureas were unprecedented. Although commercial “oxidatively resistant” thermoplastic polyurethanes degraded severely upon exposure to boiling water or concentrated nitric acid, the experimental polyureas survived without much degradation in properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 38–48, 2009     

Polyisobutylene‐based polyurethanes with unprecedented properties and how they came about

This highlight concerns the birth, development, and present status of unique polyurethanes consisting of polyisobutylene soft segments and conventional hard segments (PIB‐based PUs) exhibiting unprecedented combinations of mechanical properties and oxidative/hydrolytic/biological stability. Impetus for developments was to improve the rather poor chemical resistance of conventional polyurethanes by replacing their soft segments with polyisobutylene segments. Research started in the 1980s with the synthesis of α,ω‐polyisobutylene diols (HO‐PIB‐OH) by the inifer technique and preparation of PIB‐based PUs, which indeed exhibited outstanding stabilities, however, had poor mechanical properties. Because of cumbersome early techniques and expensive reagents, worldwide research and industrial interest waned and developments went into hibernation. Recent discoveries, including living isobutylene polymerization, improved end‐functionalizations, inexpensive ingredients, and new insight into PU morphology, lead to simple and less expensive synthesis strategies and, consequently, to resumption of fundamental and applied research. Presently, we can produce kilogram quantities of polyurethanes and polyureas with unprecedented combinations of excellent physical–mechanical–environmental–biological and processing properties. This highlight focuses on facts and insights, which occurred since the discovery and shaped developments. These events are worth reviewing and analyzing because they illustrate how contemporary academic research is driven by curiosity (fun) and economic considerations (money). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Morphology and tensile properties of model thermoplastic polyurethanes with MDI/butanediol based monodisperse hard segments

Morphology and tensile properties of model thermoplastic polyurethanes (TPUs) containing polyisobutylene (PIB) or poly(tetramethylene oxide) (PTMO) based soft segment and 4,4‐methylene bis(phenyl isocyanate) (MDI) and 1,4‐butanediol (BDO) based monodisperse hard segments (HSs), consisting of exactly two to four MDI units extended by BDO, were investigated. Using FT‐IR spectroscopy, increased hydrogen bonded C?O fraction was observed in model TPUs as the HS size increased. The hydrogen bonded C?O fraction was higher in PIB based TPUs compared with PTMO based TPUs, indicating higher phase separation in PIB based TPUs. The morphology of TPUs was investigated using AFM phase imaging, which showed ribbon‐like or interconnected hard domains in PTMO based model TPUs and randomly dispersed hard domains in PIB based model TPUs. SAXS revealed that the degree of phase separation in the model TPUs was higher than in their polydisperse analogues. Domain spacing as well as interfacial thickness increased with the increasing HS size, and both values were higher in PTMO based TPUs. The tensile analysis indicated that model TPUs exhibited higher modulus and slightly higher elongation compared with their polydisperse analogues. Only in PTMO based model TPUs, strain induced crystallization was observed above 300% elongation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2485–2493     

Polyisobutylene‐based polyurethanes: VII. structure/property investigations for medical applications

The outstanding hydrolytic and oxidative stabilities of polyisobutylene‐based polyurethanes (PIB‐based PUs) were reported earlier. Herein, we summarize recent investigations aimed at further enhancing hydrolytic‐oxidative stabilities (in terms of resistance to aqueous buffer, nitric acid and CoCl₂/H₂O₂) together with excellent mechanical properties. The purity and dryness of ingredients together with precise NCO/OH stoichiometry (～1.05) are essential to obtain PIB‐based PUs with improved properties. Static and dynamic mechanical properties were optimized by analyzing stress–strain traces, thermal (TGA, DSC) responses, self‐organization (XRD) profiles, and rheological (DMA, creep) information. According to microstructure and surface analyses (AFM, contact angle) annealing increases the segregation of individual segments and increases surface hydrophobicity, which in turn enhances the shielding of hydrolytically oxidatively vulnerable carbamate bonds by inert PIB barriers, and thus significantly improves hydrolytic‐oxidative stability. Annealing does not much affect bulk properties, such as static and dynamic mechanical and thermal properties; however, it increases damping over a wide temperature range. Annealed PIB‐based PU containing 72.5% PIB exhibits outstanding hydrolytic‐oxidative stability together with ～26 MPa tensile strength, ～500% elongation, and ～77 Microshore hardness. PIB‐based PUs are significantly more resistant to hydrolytic and oxidative degradation than ElastEon? E2A, a commercially available PDMS‐based PU, widely used for medical applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 532–543     

Polyisobutylene‐based polyurethanes. VI. Unprecedented combination of mechanical properties and oxidative/hydrolytic stability by H‐bond acceptor chain extenders

We describe the design, synthesis, characterization, and testing of novel polyurethanes (PUs) exhibiting unprecedented combinations of outstanding mechanical properties and oxidative/hydrolytic stabilities. This achievement is due to the use of polyisobutylene (PIB) soft segments plus flexible H‐bond acceptor chain extenders (HACEs): the PIB imparts superior oxidative/hydrolytic stability and the HACE produces reinforcing H‐bonds, which lead to outstanding mechanicals. Oxidative/hydrolytic stability was quantitated by retention of tensile strength and elongation after exposure to nitric acid. PUs containing 60–70% PIB retain their mechanical properties, whereas Carbothane®, Bionate®, and Elast‐Eon?, PUs marketed for chemical stability, degrade severely under the same conditions. Various HACEs were identified (e.g., hexaethylene glycol, tripropylene glycol, tributylene glycol, 3,3′‐diamino‐N‐methyl‐dipropylamine, etc.) and their effect on mechanical properties was investigated. A PIB‐ and HACE‐containing PU exhibited 29.2 MPa tensile strength, 620% elongation, and 80 Shore A hardness. Properties were analyzed in terms of stress–strain profiles, differential scanning calorimetry traces, dynamic mechanical thermal analysis plots, and oxidative/hydrolytic stability. The properties of various PIB‐based rubbers, that is, thermoplastic PUs, SIBSTAR®, and thermoset butyl rubber are compared. The novel PUs are promising candidates for biomaterials and industrial applications where a combination of mechanical properties and oxidative/hydrolytic stability is of the essence. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2361–2371, 2010     

Synthesis and thermal transition behavior of model thermoplastic polyurethanes containing MDI/butanediol‐based monodisperse hard segments

Amine‐terminated monodisperse hard segments (MDHSs) containing two to four 4,4′‐methylenebis (phenyl isocyanate) extended by 1,4‐butanediol have been synthesized using carboxybenzyl protecting‐deprotecting strategy. Pure MDHSs in large scale were obtained in good yield and their structures were confirmed by ¹H‐, ¹³C‐NMR spectroscopy and GPC‐MALLS. Differential scanning calorimetry (DSC) showed that as the hard segment (HS) size increased, the melting and glass transition temperature and the change of heat capacity at glass transition of ethyl capped MDHSs increased. Model thermoplastic polyurethanes (TPUs) were synthesized using the reaction of bischloroformate of poly (tetramethylene oxide) (PTMO) diol or polyisobutylene (PIB) diol with amine‐terminated MDHSs. X‐ray diffraction results indicated the amorphous structure of model TPUs. DSC revealed HS related endotherms, regardless of SS, which were attributed to the local ordering of the HSs. Additional endotherms in PTMO based model TPUs might arise from the dissociation of hydrogen bonding between PTMO and HSs. The lower T_g in model TPUs compared to the polydisperse analogues observed by dynamic mechanical analysis (DMA) indicated higher microphase separation of monodisperse HSs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3171–3181     

Morphology and Mechanical Properties of Thermoplastic Polyurethanes Containing Polyisobutylene/Poly(tetramethylene oxide) Mixed Segments

We investigated the thermal properties, microphase separated structure and mechanical properties of a series of thermoplastic polyurethanes (TPUs) containing both polyisobutylene (PIB) and poly(tetramethylene oxide) (PTMO) diols in the soft segment (SS). A series of TPUs were prepared with the same weight fraction of the SS but different ratio between PIB and PTMO diols. Molecular weight of the PTMO diol and chemical structure of the hard segment (HS) also varied. Dynamic mechanical analysis (DMA) measurements did not reveal strong microphase separation between PIB and PTMO in the SS. While it has been assumed that incorporating PTMO diol into the SS can enhance the phase mixing between the hard segment (HS) and SS, our results indicated that, in most cases, the degree of microphase separation of TPUs based on mixed diols is slightly higher than that of TPUs based on only PIB diol.     

Metallo‐supramolecular Crosslinked Polyurethanes

The effects of incorporating metal‐binding ligands as chain extenders in polyurethane elastomers were investigated. Segmented polyurethanes based on 2 kDa poly(tetramethylene oxide) (PTMO) and 4,4‐methylenebis(cyclohexyl isocyanate) were polymerized using a two‐step process in which 2,6‐bis(1‐ethyl‐5‐(methoxymethyl)‐1H‐benzo[d]imidazol‐2‐yl)pyridine was added as a chain extender. The resulting polyurethanes were then metallated using stoichiometric amounts of Zn(II) metal salts with different counterions. The resulting metallopolymers have substantially improved Young's moduli, increased failure stress, and improved thermomechanical behavior. The materials were microphase‐separated into anisotropic hard domains within a PTMO matrix. Simultaneous small‐angle X‐ray scattering and tensile testing revealed the minority hard segment domains remain relatively intact during elongation, likely due to the strength of the metal–ligand complex. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1744–1757     

Polyisobutylene‐based polyurethanes. IX. synthesis,characterization, and properties of polyisobutylene‐based poly(urethane‐ureas)

Polyisobutylene (PIB)‐based polyurethanes (PUs) exhibit unparalleled hydrolytic‐oxidative‐biologic stability and are melt processible, however, their mechanical (strength) properties are modest mainly due to insufficient H bonds. We posited and demonstrate that the ultimate properties of PIB‐PUs are enhanced, while their melt processibility is maintained, by the judicious introduction of urea linkages, i.e., strong bifurcated H bonds, in the chain. The incorporation of bifurcated H bonds in PIB‐PUs was achieved by using the conventional butane diol chain extender (CE) in combination with controlled amounts of amino alcohol as co‐chain extender (co‐CE). Polyurethanes containing both urethane and urea linkages are polyurethane‐ureas (PUU). Specifically, PIB‐PUUs prepared with PIB‐diol/MDI together with 80/20 mole % butane diol/amino butanol exhibited ～30 MPa tensile strength, ～550% elongation, ～80 Shore A hardness, and ～137 °C flow temperature. Other amino alcohols, i.e., amino ethanol, ‐propanol, and ‐hexanol, were less effective co‐CEs. ¹H‐NMR and FT‐IR spectroscopies indicate the presence of bifurcated H bonds in PIB‐PUUs prepared with CE/co‐CE combinations. Characterization by differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical thermal analysis, and creep experiments also suggest bifurcated H bonds in PIB‐PUU. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2361–2369     

Shape‐memory behavior of segmented polyurethanes with an amorphous reversible phase: The effect of block length and content

Segmented thermoplastic polyurethanes (TPU)s with amorphous soft segments from the reaction of hexamethylene diisocyanate and 1,2‐butanediol and crystalline hard segments from 4,4′‐methylenediphenyl diisocyanate and 1,6‐hexanediol showed sharp glass‐transition temperatures that could be used as shape‐recovery temperatures. The thermal, mechanical, and shape‐memory effect of these TPUs of various block compositions and lengths were studied by differential scanning calorimetry, dynamic mechanical testing, and tensile testing. As the block lengths decreased, phase mixing increased and hysteresis in the shape‐memory behavior decreased. Too low a content of hard segments increased the hysteresis in the shape‐memory behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2652–2657, 2000     

Polyisobutylene‐based polyurethanes X: PU nanocomposites with s‐containing soft segments

Sulfur‐containing polyisobutylene (PIB)‐based polyurethane nanocomposite (PIB_s‐PU/NC) was synthesized using HO? CH₂CH₂? S? PIB? S? CH₂CH₂? OH for the soft segment, conventional hard segments of MDI and BDO, and organically modified montmorillonite (OmMMT) nanolayers. The properties of PIB_s‐PU/NC containing 72.5% PIB and 0.5% OmMMT were studied and contrasted with unmodified PIB_s‐PU. PIB_s‐PU/NC produces colorless optically clear films exhibiting enhanced tensile strength, elongation, oxidative–hydrolytic stability, and creep resistance relative to that of PIB_s‐PU. FTIR spectroscopy indicates H bonded S atoms between soft and hard segments, and OmMMT nanolayers. DSC and XRD suggest randomly dispersed low‐periodicity crystals and urea groups between galleries. We propose that minute amounts of OmMMT nanolayers become covalently attached to polyurethane chains and beneficially affect properties by acting as co‐chain extender/reinforcing filler. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2760–2765     

Polyisobutylene‐based polyurethanes. VIII. Polyurethanes with ‐O‐S‐PIB‐S‐O‐ soft segments

We describe the synthesis, characterization, and select properties of a novel polyurethane (PU) prepared using a new polyisobutylene diol, HO‐CH₂CH₂‐S‐PIB‐S‐CH₂CH₂‐OH, soft segment and conventional hard segments. The diol is synthesized by terminal functionalization of ally‐telechelic PIB followed by low‐cost thiol‐ene click chemistry. Properties of ‐S‐ containing PU (PIB_S‐PU) containing 72.5% PIB were investigated and compared to similar PUs made with HO‐PIB‐OH (PIB_O‐PU). Hydrolytic resistance was studied by contact with phosphate‐buffered saline, oxidative resistance by immersing in concentrated HNO₃, and metal ion oxidation resistance by exposure to CoCl₂/H₂O₂. Hydrolytic and oxidative resistances of PIB_S‐PU and PIB_O‐PU are similar and superior to a commercial PDMS‐based PU, Elast‐Eon? E2A. According to ¹H NMR spectroscopy the ‐S‐ in PIB_S‐PUs remained unchanged upon treatment with HNO₃, however, oxidized mainly to ‐SO₂‐ by CoCl₂/H₂O_2. Static mechanical properties of PIB_S‐PU and PIB_O‐PU are similar, except creep resistance of PIB_S‐PU is surprisingly superior. The thermal stability of PIB_S‐PUs is ～15 °C higher than that of PIB_O‐PU. FTIR spectroscopy indicates H bonded S atoms (N‐H…S) between soft and hard segments, which noticeably affect properties. DSC and XRD studies suggest random low‐periodicity crystals dispersed within a soft matrix. Energy dispersive X‐ray spectroscopy–scanning electron microscopy indicates homogeneous distribution of S atoms on PIB_S‐PU surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1119–1131     

Temperature‐dependent changes in the hydrogen bonded hard segment network and microphase morphology in a model polyurethane: Experimental and simulation studies

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. 2018 , 56, 182–192     

Micro‐phase‐separation behavior of amphiphilic polyurethanes involving poly(ethylene oxide) and poly(tetramethylene oxide)

The temperature dependence of thermal, morphological, and rheological properties of amphiphilic polyurethanes was examined with differential scanning calorimetry (DSC), wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering (SAXS), rheological measurements, and Fourier transform infrared spectroscopy. Multiblock (MPU) and triblock (TPU) polyurethanes were synthesized with two crystallizable segments—poly(ethylene oxide) (PEO) as a hydrophilic block and poly(tetramethylene oxide) (PTMO) as a hydrophobic block. DSC and WAXS measurements demonstrated that the microphase of MPUs in the solid state is dominantly affected by the PEO crystalline phase. However, high‐order peaks were not observed in the SAXS measurements because the crystallization of the PEO segments in MPUs was retarded by poor sequence regularity. The microphase in the melt state was induced by the hydrogen bonding between the N? H group of hexamethylene diisocyanate linkers and the ether oxygen of PEO or PTMO blocks. As the temperature increased, the smaller micro‐phase‐separated domains were merged into the larger domains, and the liquidlike ordering was eventually disrupted because of the weakening hydrogen bonding. However, the fully homogeneous state of an MPU with a molar ratio of 5/5 PEO/PTMO (MPU55) was not confirmed even at much higher temperatures with both SAXS and rheological measurements. However, the SAXS patterns of TPU showed weak but broad second‐order peaks below the melting temperature of the PEO block. Compared with MPU55, the ordering of the TPU crystalline lamellar stacks was enhanced because of the high sequence regularity and the low hydrogen‐bonding density. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2365–2374, 2003     

Pi‐conjugated chain extenders for the synthesis of optoelectronic segmented polyurethanes

The optical properties of mechanochromic materials change under mechanical stress. Segmented polyurethanes are elastomers composed of amorphous, saturated chain soft segments, and rigid pi‐conjugated hard domains. Within aggregates of hard domains pi–pi interactions may form and result in perturbation of the optoelectronic properties of the system. Disruption and restoration of these electronic interactions within the material may lead to observable mechanochromic response. A series of oligothiophene diols and diamines, as well as a naphthalene diimide diol, have been synthesized for incorporation into the hard domains of segmented polyurethanes and polyureas using long poly(tetramethylene oxide) chains as soft segments. The resulting polymers were evaluated to determine their extent of polymerization and their thermal stability. The optical properties of the materials were studied in solution and as thin films. Where possible the electrochemical properties of the polymers were also explored. The length of the soft segment chains in the segmented polyurethanes hindered electronic coupling of hard domains. Future work involving smaller, more solubilizing soft segments may allow for easier material characterization and mechanochromic response. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Sugar‐based hydrophilic polyurethanes and polyureas

Novel linear homogeneous polyurethanes and polyureas with enhanced hydrophilic character have been successfully prepared from sugar‐based monomers having their hydroxyl groups free or partially protected. By the reaction of primary hydroxyl groups of xylitol with dimethyl hexamethylene dicarbamate (HMDC) or di‐tert‐butyl‐4,4′‐diphenyl methyl dicarbamate (MDC), two new linear semicrystalline polyurethanes [PU(X‐HMDC) and PU(X‐MDC)] have been prepared. Likewise, by the reaction of xylitol with the analogous diisocyanates hexamethylene diisocyanate (HMDI) or 4,4′‐methylenebis(phenyl isocyanate) (MDI), similar polyurethanes [PU(X‐HMDI) and PU(X‐MDI)] were obtained. However, these latter polyurethanes present some degree of crosslinking because of the higher reactivity of the diisocyanate comonomers. Linear hydrophilic polyureas having free hydroxyl groups joined to the main chain have also been prepared by the reaction of the same diisocyanates (HMDI and MDI) with 1,6‐diamino‐1,6‐dideoxy‐D ‐mannitol and 1,6‐diamino‐1,6‐dideoxy‐3:4‐O‐isopropylidene‐D ‐mannitol. As far as we are aware, this kind of polyhydroxylated polyurea has not been previously described in the literature. The new polymers were characterized by standard methods (elemental analyses, gel permeation chromatography, IR, and NMR). The polyurethanes were hydrolytically degradable under physiological conditions, in contrast with less‐hydrophilic linear polyurethanes previously described. The thermal properties of the novel polymers were investigated by thermogravimetric analysis and differential scanning calorimetry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and properties of segmented main‐chain liquid‐crystalline polyurethanes with a high aspect ratio mesogenic diol as a chain extender

Main‐chain liquid‐crystalline polyurethanes were synthesized based on a high aspect ratio mesogenic diol (4‐{[4‐(6‐hydroxyhexyloxy)‐phenylimino]‐methyl}‐benzoic acid 4‐{[4‐(6‐hydroxyhexyloxy)‐phenylimino]‐methyl}‐phenyl ester) as a chain extender; polycaprolactone (PCL) diol soft segments of different number‐average molecular weights (530, 1250, or 2000); and different diisocyanates, including 1,4‐hexamethylene diisocyanate (HMDI), 4,4′‐methylene bis(cyclohexyl isocyanate) (H₁₂MDI), and 4,4′‐methylene bis(phenyl isocyanate) (MDI). The structure of the polymers was confirmed with Fourier transform infrared spectroscopy, and differential scanning calorimetry and polarizing microscopy measurements were carried out to examine the liquid‐crystalline and thermal properties of the polyurethanes, respectively. The mesogenic diol was partially replaced with 20–50 mol % PCL. A 20 mol % mesogen content was sufficient to impart a liquid crystalline property to all the polymers. The partial replacement of the mesogenic diol with PCL of various molecular weights, as well as the various diisocyanates, influenced the phase transitions and the occurrence of mesophase textures. Characteristic liquid‐crystalline textures were observed when a sufficient content of the mesogenic diol was present. Depending on the flexible spacer length and the mesogenic content, grained and threadlike textures were obtained for the HMDI and H₁₂MDI series polymers, whereas the polyurethanes prepared from MDI showed only grained textures for all the compositions. The polymers formed brittle films and could not be subjected to tensile tests. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1527–1538, 2002