Electrospinning of linear and highly branched segmented poly(urethane urea)s

Electrospun fibrous mats were formed from linear and highly branched poly(urethane urea)s. The highly branched poly(urethane urea)s were synthesized using an A₂+B₃ methodology, where the A₂ species is an oligomeric soft segment. Since the molecular weight of the A₂ oligomer is above the entanglement molecular weight, the highly branched polymers formed electrospun fibers unlike typical hyperbranched polymers that do not entangle. Stress-strain experiments revealed superior elongation for the electrospun fibrous mats. In particular, the highly branched fiber mats did not fail at 1300% elongation, making the electrospun mats promising for potential applications where enhanced tear strength resistance is required.     

The effect of microstructure on the rate-dependent stress-strain behavior of poly(urethane urea) elastomers

Segmented poly(urethane urea) materials (PUUs) exhibit versatile mechanical properties and have drawn great interest due to their potential for protection against projectile impacts and blast loadings. To optimize the performance of PUUs for various high rate applications, specific features of their mechanical behavior have to be suitably tailored by altering the microstructure. Hence the micromechanisms governing the mechanical behavior must be identified, understood and leveraged. In this study, the effects of varying microstructure on the rate-dependent mechanical behavior were examined for select PUU materials. As expected, increasing the hard segment content increased the stiffness and the flow stress levels. Interestingly, it was observed that promoting phase mixing among the hard and soft segment domains of the PUU material greatly enhanced its rate-dependent stiffening and strain hardening behavior. These insights can help design PUUs for articles that manifest improved protective abilities under impact, while maintaining their flexibility during normal use. The potential applications for such materials are extensive, including face masks and goggles, which require excellent folding/un-folding capabilities, while also providing superior impact resistance.     

New insight into microstructure-mediated segmental dynamics in select model poly(urethane urea) elastomers

Segmental dynamics in a series of 4,4′-dicyclohexylmethane diisocyanate–diethyltoluenediamine–poly(tetramethylene oxide) based poly(urethane urea) (PUU) elastomers have been investigated through a multi-scale characterization approach. This includes broadband dielectric analysis, solid-state nuclear magnetic resonance (NMR), plate impact, and impulsive stimulated scattering. Dielectric relaxation measurements applicable at frequencies up to 10⁶ Hz are useful for interpreting the high strain-rate deformation response; i.e. at the moment of target interaction with an accelerating impact or MHz stress wave excitation. Additionally, the capability of solid-state NMR to differentiate the microstructure-mediated segmental dynamics; correspondingly, the presence of a rigid phase (those in the phase-mixed regions) and a mobile phase associated with the soft-segment domains is demonstrated. These new insights not only further elucidate the microstructure details discerned through atomic force microscopy, but also enable the prediction of the macroscopically dynamic response in these model PUUs, particularly on the temporal scale over the range of μs–ns.     

Phase-mixing and molecular dynamics in poly(urethane urea) elastomers by solid-state NMR

The dynamical heterogeneity in a series of 4,4′-dicyclohexylmethane diisocyanate-diethyltoluenediamine-poly(tetramethylene oxide) based poly(urethane urea) (PUU) elastomers was studied by solid-state nuclear magnetic resonance (NMR) methods. Extensive phase mixing was evidenced by the ¹H wideline signal, which can be approximately fitted by a single exponential model. ¹³C T₁ relaxation time measurements indicate that the hard segments (HS) exhibit some small-amplitude mobility, likely “activated” by neighboring soft segments (SS). Fitting of the time-domain wideline separation (TD-WISE) data was employed to characterize the extent of phase mixing, which revealed that a PUU elastomer contains four fractions: rigid-HS, mobile-HS, rigid-SS, and mobile-SS regions. For a variety of SS MWs, the dynamics and relative portions of rigid vs. mobile fractions among HS were substantially similar, while those for the SS exhibit large contrast. Furthermore, the dynamics in the rigid-SS fraction is at least an order of magnitude slower than that in mobile-SS for all PUUs. Greater phase-mixing substantially lowers the SS mobility, facilitating SS to undergo glass transition at high strain rates, thus can be key to enhancing dynamic mechanical strengthening.     

Hydrophilic porous polymers based on high internal phase emulsions solely stabilized by poly(urethane urea) nanoparticles

Stable oil-in-water (o/w) Pickering high internal phase emulsions (HIPEs) having an internal phase of up to 95 vol% were prepared with a low-energy emulsification method. A poly(urethane urea) (PUU) aqueous nanodispersion was used as aqueous phase. The PUU nanoparticles of the aqueous nanodispersion acted as a mechanical barrier, and prevented droplet coalescence in the Pickering HIPEs. In addition, open porous hydrophilic polymer foams were obtained by polymerization of the Pickering HIPEs, and the morphology of the foams were tailored by changing the oil:water ratio, PUU nanoparticle and NaCl concentrations. The method used herein provides a simple way to prepare morphology controlled hydrophilic polymer foams using o/w Pickering HIPEs as template.     

Simple and versatile method for the one‐pot synthesis of segmented poly(urethane urea)s via in situ‐formed AB‐type macromonomers

We present a one‐pot method for the synthesis of poly(urethane urea)s (PUUs) with uniform (monodisperse) hard segments that eliminates tedious approaches to control the exothermic nature of isocyanate–amine reaction, is less sensitive to impurities and involves no isolation of intermediates. Reaction of two moles of hexamethylene diisocyanate with one mole of polycaprolactone of various molecular weights under optimum time and temperature led to NCO‐terminated polyurethane prepolymers. Addition of an equimolar quantity of benzoic acid and excess dimethylsulfoxide at ambient temperature produced quantitative yields of PUUs with high molecular weight. The structure of the PUUs was fully characterized using spectroscopic methods and a reasonable mechanism for the reaction sequences was determined via preparation and characterization of a model compound. Dynamic mechanical thermal analysis data confirmed the phase‐separated structure of the PUUs. Evaluation of stress‐strain curves revealed the wide‐ranging mechanical properties depending on soft‐segment molecular weight. Monitoring the remaining weight and molecular weight of polymers incubated in phosphate‐buffered saline showed hydrolytic degradability with rate depending on soft‐segment molecular weight. Also, a preliminary investigation of the interaction of L929 fibroblast cells with the prepared polymers confirmed no cytotoxicity and acceptable cytocompatibility for the PUUs. Copyright © 2010 Society of Chemical Industry     

Preparation and Characterization of Structurally Graded Poly(urethane urea) Elastomers

Poly(urethane urea) elastomers with graded structure in the thickness direction were prepared using gradient temperature molding. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to characterize the gradual change of structures within the elastomers. The degree of microphase separation in prepared samples would increase gradually with the increase of the curing temperature. Moreover, the interfaces between hard and soft segments also exhibit gradual changing trend, becoming more significant along the same direction. Effect of chain extender content and magnitude of temperature gradient on structure gradient was investigated. Mechanical properties of graded poly(urethane urea) elastomers were also studied.     

Synthesis, characterization and biodegradation studies of poly(ester urethane)s

Bis-isocyanoto polyester was synthesized by the polymerization of PPSe with MDI and reacted with 1,3-propanediol chain extender to obtain poly(ester urethane)s. The effect of chain extender and PPSe content in polyurethane was investigated. The polymers were characterized by ¹H NMR, FT-IR, viscosity measurement, TGA and XRD. Their biodegradability was investigated by the hydrolytic degradation in NaOH solution (3% and 10%); enzymatic degradation by Rhizopus delemar lipase and soil burial degradation using garden-composted soil. Furthermore, the degraded film was characterized by molecular weight, intrinsic viscosity, DSC, XRD, FT-IR and surface morphology by SEM. The biodegradation study revealed that hydrolysis and soil burial degradation affected morphology of the PEUs. Hydrophobicity and hard segment seem to resist the hydrolytic and enzymatic degradability of PEU. Hydrolytic degradation was very rapid in 3% and 10% NaOH solutions at 37 °C, within 2 days 20% weight loss was observed. PEUs showed a much slower degradation rate under the R. delemar lipase at 37 °C. Experimental data showed that as soft segment increases biodegradation rate decreased. A significant rate of degradation was occurred in all PEU samples under soil burial condition. Surface morphology, which interconnected to good adhesion of bacteria on polymer surface, is considered to be a factor sensible for the biodegradation rate under soil burial condition.     

Influence of compositional variables on the morphological and dynamic mechanical behavior of fatty acid based self-crosslinking poly (urethane urea) anionomers

Fatty acid based self-crosslinking polyurethane urea (PUU) anionomers can find potential applications in coatings field due to enhanced chemical resistance properties. To optimize their performance in coatings, the molecular features that influence the microphase morphology and dynamic mechanical (DM) behavior of polymer films must be understood and exploited. In this work, comprehensive materials characterization of model PUU anionomers films with oxidative-crosslinking microstructure is addressed. For this, linoleic fatty acid based precursor (LPE) was included in polymer backbone which provides reactive sites for autooxidative polymerization. Three series of compositions were prepared with urea content of 8.4%, 13.2% and 18.1% where within each series LPE content has been increasing in same proportion. Different experimental techniques like FTIR, DSC, DMA and mechanical testing were utilized to study the effect of compositional variables on the extent of phase segregation, domain structure and mechanical properties of fully cured polymer samples. The extent soft segment (SS) oxidative crosslinking had marked effect on the microphase morphology and DM properties of materials of lowest urea content. Significant phase mixing was observed with evolvement of single heterogenous phase in the sample with highest LPE content. Samples with 13.2% urea shows less sensitivity toward increased SS crosslinking in their microphase morphology change. Their mechanical and DM properties were observed to be dominated by interlocked hard domains. With higher urea content, such kind of hard segment cohesion results due to greater strength of bidenate H-bonding among urea linkages. While samples with highest % urea, were clearly found to be well microphase separated compared to other two series with highest HS interconnectivity and have marginal effect of extent of SS crosslinking on microphase separation. This study gives an insight about effect of extent of complex oxidative crosslinking on the microphase separation and DM behavior of segmented PUU anionomers based films with different urea content which is useful in designing such materials in coating system with specific surface structure and function.     

pH- and temperature-sensitive multiblock copolymer hydrogels composed of poly(ethylene glycol) and poly(amino urethane)

A series of novel pH- and temperature-responsive multiblock copolymers (poly(PEG/HEP urethane)) consisting of poly(ethylene glycol) (PEG) and poly(amino urethane) (PAU) were synthesized, and their physicochemical properties were studied. The amphiphilic block copolymers were synthesized from PEG, 1,4-bis(hydroxyethyl) piperazine (HEP) and 1,6-diisocyanato hexamethylene (HDI) in the presence of dibutyltin dilaurate as a catalyst. The resulting polymers were examined by FT-IR, ¹H and ¹³C NMR spectroscopies and gel permeation chromatography (GPC). The solution properties of the copolymers were studied by turbidity measurement and fluorescence spectroscopy. The copolymers showed a pH-dependent soluble-insoluble transition in diluted aqueous solutions. The concentrated polymer solutions exhibited a thermo-induced sol-gel-sol phase transition at pH 6.8-7.4. The gel window covers the physiological conditions. After a subcutaneous injection of the multiblock copolymer solution into mice, a transparent and soft gel was formed immediately. The in vitro release of a model anticancer drug, chlorambucil, persisted over 2 weeks under physiological conditions.     

Synthesis, characterization and degradation of biodegradable thermoplastic elastomers from poly(ester urethane)s and renewable soy protein isolate biopolymer

New biodegradable poly(ester urethane)/soy protein isolate (PEU/SPI) hybrids were prepared by in situ polymerization. The chemical incorporation of the SPI into the backbone chain of the PEU was facilitated by the reaction of the amine functional groups of SPI with methylene diphenyl diisocyanate (MDI). X-ray diffraction results showed that the chemical incorporation of SPI into PEU significantly changed the molecular structure of the PEU. The PEU/SPI hybrids exhibited higher thermal decomposition temperature and significant increase in the modulus compared with that of pure PEU. Microscopic examination of the morphology of PEU/SPI hybrids confirmed very fine and homogeneous SPI dispersion in PEU. The hydrolytic degradation of the PEU in a phosphate buffer solution was accelerated by incorporation of SPI, which was confirmed by water absorption and scanning electron microscopy of the samples after up to 10 weeks immersion in the buffer solution. This study provides a facile and innovative method of controlling the biodegradation rate of pure PEU with the additional advantage of environmentally-benign biodegradation of the hybrid PEU/SPI polymer, making the concept potentially widely applicable.     

pH/temperature-sensitive 4-arm poly(ethylene glycol)-poly(amino urethane) copolymer hydrogels

A series of novel pH/temperature-sensitive 4-arm poly(ethylene glycol)-poly(amino urethane) copolymers was synthesized via addition polymerization. The resulting copolymers were characterized by ¹H, ¹³C NMR, Fourier transform infrared spectroscopy and gel permeation chromatography. Poly(amino urethane) (PAU) segment acts as a pH/temperature-sensitive block. The copolymer aqueous solutions showed a sol-to-gel-to-aggregation phase transition as a function of pH and temperature when the pH of the copolymer solution is higher than 6.8. The sol-gel phase transition could be controlled by varying the PAU block length and copolymer concentration. The gel window covers the physiological conditions and a white gel was formed rapidly after subcutaneously injecting the copolymer solution (30 wt%) into SD rats. The in vitro release of chlorambucil, an anticancer drug, was sustained over 14 days under physiological conditions.     

Synthesis,characterization, and pervaporation properties of segmented poly(urethane‐urea)s

Poly(urethane‐urea)s (PUUs) from 2,4‐tolylene diisocyanate (2,4‐TDI), poly(oxytetramethylene)diols (PTMO) or poly(butylene adipate)diol (PBA), and various diamines were synthesized and characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, and density measurements. Transport properties of the dense PUU‐based membranes were investigated in the pervaporation of benzene–cyclohexane mixtures. It was shown that the pervaporation characteristics of the prepared membranes depend on the structure and length of the PUU segments. The PBA‐based PUUs exhibit good pervaporation performance along with a very good durability in separation of the azeotropic benzene–cyclohexane mixture. They are characterized by the flux value of 25.5 (kg μm m⁻² h⁻¹) and the separation factor of 5.8 at 25°C, which is a reasonable compromise between the both transport parameters. The PTMO‐based PUUs display high permeation flux and low selectivity in separation of the benzene‐rich mixtures. At the feed composition of 5% benzene in cyclohexane, their selectivity and flux are in the range of 3.2 to 11.7 and 0.4 to 40.3, respectively, depending on the length of the hard and soft segments. The chemical constitution of the hard segments resulting from the chain extender used does not affect the selectivity of the PUU membranes. It enables, however, the permeability of the membranes to be tailored. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1615–1625, 1999     

The synthesis, characterization and biocompatibility of poly(ester urethane)/polyhedral oligomeric silesquioxane nanocomposites

The primary goal of this study is to develop a facile and inexpensive synthesis method for a new biodegradable and biocompatible poly(ester urethane) (PEU)/polyhedral oligomeric silesquioxanes (POSS) nanocomposite via in situ homogeneous solution polymerization reaction into prescribed macromolecular structure and properties including improved biocompatibility, thermal and hydrolytic stability, and stiffness and strength. Cell culture studies, nuclear magnetic resonance spectroscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetry, and dynamic mechanical analysis measurements were used to confirm the structure and property improvements. The results show that the targeted PEU/POSS nanocomposites (which are remarkably different from conventional polymers, polymer nanocomposites and microcomposites) have significant improvements in mechanical properties and degradation resistance at small POSS concentrations (≤6 wt%). The nanocomposites exhibited excellent support for cell growth without any toxicity. POSS concentration did not affect cell adhesion or cell growth, but it significantly changed the surface structure of the PEU into a 3-dimensional matrix with regular pores that may allow cells to better access the growth factors/nutrients, waste exchange, and tissue remodeling. The PEU/POSS nanocomposites were resistant to degradation over a period of six months when exposed to a buffer solution. These desirable characteristics suggest that the nanocomposites may hold great promise for future high-end uses such as in biomedical devices, especially at cardiovascular interfaces.     

Effect of Soft Segment Length and Chain Extender Structure on Phase Separation and Morphology in Poly(urethane urea)s

The phase separation and morphology in poly(urethane urea)s were investigated as soft segment length and chain extender structure were varied. Increases in soft segment length led to increased phase separation that resulted in greater mobility of the soft segment. This was shown by lower soft segment glass transition temperatures in differential scanning calorimetry (DSC) as well as a shift of E_max″ and tan δ_max to lower temperatures. Also the structure of the chain extender affected the degree of phase separation and mixing of the soft and the hard blocks in an interphase. Atomic force microscopy (AFM) was used to visualize the structure of the phase‐separated domains. The hard domains were in the form of spheres 5–10 nm, or long needles 5 nm thick and 50–300 nm long. As the soft segment length increased, there were more pure soft segment phase areas between the hard domains. At high hard segment content, a larger scale structure was found, consisting of both hard and soft segments.

DSC thermograms of poly(urethane urea)s containing different soft segment lengths.     

Influences of poly(ether urethane) introduction on poly(ethylene oxide) based polymer electrolyte for solvent-free dye-sensitized solar cells

A poly(ether urethane) (PEUR)/poly(ethylene oxide) (PEO)/SiO₂ based nanocomposite polymer is prepared and employed in the construction of high efficiency all-solid-state dye-sensitized nanocrystalline solar cells. The introduction of low-molecular weight PEUR prepolymer into PEO electrolyte has greatly enhance the electrolyte performance by both improving the interfacial contact properties of electrode/electrolyte and decreasing the PEO crystallization, which were confirmed by XRD and SEM characteristics. The effects of polymer composition, nano SiO₂ content on the ionic conductivity and I₃⁻ ions diffusion of polymer-blend electrolyte are investigated. The optimized composition yields an energy conversion efficiency of 3.71% under irradiation by white light (100 mW cm⁻²).     

A novel biodegradable multiblock poly(ester urethane) containing poly(l-lactic acid) and poly(butylene succinate) blocks

A novel biodegradable multiblock poly(ester urethane) (PEU), consisting of poly(l-lactic acid) (PLLA) and poly(butylene succinate) (PBS) blocks, has been successfully synthesized via chain-extension reaction of dihydroxyl terminated PLLA (PLLA-OH) and PBS prepolymers (PBS-OH) using toluene-2,4-diisocyanate (TDI) as a chain extender. The chemical structures and molecular weights of PEUs, containing different block lengths and weight fractions of PLLA and PBS, were characterized by ¹H NMR and GPC. The effects of the structures on the physical properties of PEUs were systematically studied by means of DSC, TGA, WAXD and tensile testing. The DSC results indicated that PLLA segment was compatible well with PBS segment in amorphous phase and the crystallization of PEU was predominantly caused by PBS segment, which was also confirmed by WAXD. The results of tensile testing showed that the extensibility of PLLA was largely improved by incorporating PBS segment. The PEU can be used as a potential substitute for some petroleum-based thermoplastics.     

Poly(urethane) cationomers from poly(propylene) glycol and isophorone diisocyanate: emulsion characteristics and tensile properties of cast films

Poly(urethane) (PU) cationomers were synthesized from poly(propylene) glycol (PPG), isophorone diisocyanate (IPDI), and N-methyldiethanolamine (MDEA) following a prepolymer mixing process. Emulsions were obtained by adding water to the prepolymer solutions. Particle size and emulsion viscosity were studied in response to the MDEA content, degree of neutralization, and solid content of emulsion. It was found that at fixed solids content emulsion viscosity can be varied over 100 times depending on the MDEA content of the prepolymer and the degree of neutralization with acetic acid. Tensile properties of the emulsion cast film showed the increase in modulus and strength with degree of neutralization, as well as MDEA content.     

Synthesis and characterization of novel thermoplastic poly(oligophosphazene‐urethane)s

BACKGROUND: Polyurethanes are some of the most popular polymers used in a variety of products, such as coatings, adhesives, flexible and rigid foams, elastomers, etc. Despite the possibility of tailoring their properties, polyurethanes suffer a serious disadvantage of poor thermal stability. Many attempts have been made in order to improve the thermal stability of polyurethanes. RESULTS: A new hydroxyl‐terminated oligomer containing sulfone groups, 2,2‐bis(4‐hydroxy‐4,4‐sulfonyldiphoneloxy)tetraphenoxyoligocyclotriphosphazene (HSPPZ), was synthesized. HSPPZ was characterized using Fourier transform infrared (FTIR), NMR and gel permeation chromatography analyses. A series of novel thermoplastic poly(oligophosphazene‐urethane)s were then synthesized via the reaction of NCO‐terminated polyurethane prepolymer with HSPPZ containing chain‐extender diols. Their structure and properties were investigated using FTIR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X‐ray diffraction, water contact angle measurement and tensile measurements. CONCLUSION: Compared to conventional thermoplastic polyurethanes, poly(oligophosphazene‐urethane)s exhibit better thermal stability, low‐temperature resistance and hydrophobicity, but their mechanical properties are slightly poorer. Copyright © 2009 Society of Chemical Industry