Structural and end‐group effects on bulk and surface properties of hyperbranched poly(urea urethane)s

The hydroxy end groups of aromatic and aliphatic hyperbranched poly‐(urea urethane)s prepared with an AA* + B*B₂ one‐pot method were modified with phenylisocyanate, butylisocyanate, and stearylisocyanate. The success of the modification reaction was verified with ¹H NMR and IR spectroscopy. Linear model poly‐(urea urethane)s were prepared, too, for comparison. The bulk properties of OH functionalized hyperbranched poly(urea urethane)s, compared with those of linear analogues and modified hyperbranched poly(urea urethane)s, were studied with differential scanning calorimetry, thermogravimetric analysis, and temperature‐dependent Fourier transform infrared measurements. Transparent and smooth thin films could be prepared from all polymer samples and were examined with a light microscope, a microglider, and an atomic force microscope. The properties of the polymer surface were examined by measurements of the contact angle and zeta potential. For all samples, the properties were mainly governed by the strong interactions of the urea and urethane units within the backbone, whereas the influence of the nature of the end groups and of the branched structure was reduced in comparison with other hyperbranched polymer systems. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3376–3393, 2005     

Dielectric relaxation and aging effect in interpenetrating network polymers of poly(urethane)-poly(methyl methacrylate)

The permittivity and loss of poly(methyl methacrylate) (PMMA) network crosslinked with trimethylol-1,1,1 propane and its interpenetrating network polymers with 10, 34, and 50% (by weight) poly(urethane) have been measured from 100 to 400 K over a frequency range of 12 to 1 × 10⁵ Hz. Two relaxation processes, γ and β, are observed in the PMMA network, and a third process, α_pu, in the 10% poly(urethane) IPN. At higher concentrations of poly(urethane), the γ process is removed from the temperature-frequency range of our study. Crosslinking in pure PMMA slows the segmental motions involved in the β process and raises its activation energy. Physical aging of the 10 wt% poly(urethane)-PMMA causes its γ process to become indiscernible and the α_pu process to become better resolved. A discussion of these results in terms of local regions of segmental motion is provided.     

Amphiphilic segmented polyurethanes as surface modifying additives

Amphiphilic segmented polyetherurethanes were prepared from methylene diphenylene diisocyanate (MDI), poly(ethylene glycol) 1500 (PEG), and a fatty acid monoglyceride as a chain extender. The polymers were not soluble in water or methanol, but dissolved readily in organic solvents. The amphiphilic properties were demonstrated as a large hysteresis in the water contact angles, exceeding 110°. The amphiphilic polymers were shown to modify the surface properties of a poly(ether urethane) (PEU) and a poly(ether urethane urea) (PEUU) when added in 1–10 wt %, presumably due to migration of the additive to the surface. The surfaces of particularly the PEU blends became highly amphiphilic, exhibiting contact angles hystereses up to 90–100°. A surface saturation effect was observed at 5% added amphiphilic polymer. A difference in the behavior of PEU and PEUU was ascribed to differences in solubility of the additive in the matrix. On long-term exposure to water the PEUU blends increased their amphiphilic behavior.     

Polymeric coating of surface modified nitinol stent with POSS-nanocomposite polymer

Stent angioplasty is a successful treatment for arterial occlusion, particularly in coronary artery disease. The clinical communities were enthusiastic about the use of drug-eluting stents; however, these stents have a tendency to be a contributory factor towards late stage thrombosis, leading to mortality in a significant number of patients per year. This work presents an innovative approach in self-expanding coronary stents preparation. We developed a new nanocomposite polymer based on polyhedral oligomeric silsesquioxanes (POSS) and poly(carbonate-urea)urethane (PCU), which is an antithrombogenic and a non-biodegradable polymer with in situ endothelialization properties. The aim of this work is to coat a NiTi stent alloy with POSS-PCU. In prolonged applications in the human body, the corrosion of the NiTi alloy can result in the release of deleterious ions which leads to unwanted biological reactions. Coating the nitinol (NiTi) surface with POSS-PCU can enhance surface resistance and improve biocompatibility. Electrohydrodynamic spraying was used as the polymer deposition process and thus a few experiments were carried out to compare this process with casting. Prior to deposition the NiTi has been surface modified. The peel strength of the deposit was studied before and after degradation of the coating. It is shown that the surface modification enhances the peel strength by 300%. It is also indicated how the adhesion strength of the POSS-PCU coating changes post-exposure to physiological solutions comprised of hydrolytic, oxidative, peroxidative and biological media. This part of the study shows that the modified NiTi presents far greater resistance to decay in peel strength compared to the non-modified NiTi.     

Highly sensitive and ultrafast response surface acoustic wave humidity sensor based on electrospun polyaniline/poly(vinyl butyral) nanofibers

Polyaniline (PANi) composite nanofibers were deposited on surface acoustic wave (SAW) resonator with a central frequency of 433 MHz to construct humidity sensors. Electrospun nanofibers of poly(methyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(vinylidene fluoride), poly(vinyl butyral) (PVB) were characterized by scanning electron microscopy, and humidity response of corresponding SAW humidity sensors were investigated. The results indicated that PVB was suitable as a matrix to form nanofibers with PANi by electrospinning (ES). Electrospun PANi/PVB nanofibers exhibited a core–sheath structure as revealed by transmittance electron microscopy. Effects of ES collection time on humidity response of SAW sensor based on PANi/PVB nanofibers were examined at room temperature. The composite nanofiber sensor exhibited very high sensitivity of ∼75 kHz/%RH from 20 to 90%RH, ultrafast response (1 s and 2 s for humidification and desiccation, respectively) and good sensing linearity. Furthermore, the sensor could detect humidity as low as 0.5%RH, suggesting its potentials for low humidity detection. Attempts were done to explain the attractive humidity sensing performance of the sensor by considering conductivity, hydrophilicity, viscoelasticity and morphology of the polymer composite nanofibers.     

Amphiphilic co-networks with moisture-induced surface segregation for high-performance nonfouling coatings

Herein we report the design of a photocurable amphiphilic co-network consisting of perfluoropolyether and poly(ethylene glycol) segments that display outstanding nonfouling characteristics with respect to spores of green fouling alga Ulva when cured under high humidity conditions. The analysis of contact angle hysteresis revealed that the poly(ethylene glycol) density at the surface was enhanced when cured under high humidity. The nonfouling behavior of nonbiocidal surfaces against marine fouling is rare because such surfaces usually reduce the adhesion of organisms rather than inhibit colonization. We propose that the resultant surface segregation of these materials induced by high humidity may be a promising strategy for achieving nonfouling materials, and such an approach is more important than simply concentrating poly(ethylene glycol) moieties at an interface because the low surface energy has been maintained in our work.     

Physical aging of an epoxy subsequent to relative humidity jumps through the glass concentration

In our previous work, we showed that the structural recovery responses of an epoxy after relative humidity (RH)-jumps through the glass concentration have similar phenomenology to, but different kinetics from, those obtained by temperature (T)-jumps. In this article, we report results from physical aging experiments of the same epoxy after RH-jumps. The results show that time-RH superposition and time–aging time superposition can be used to describe the viscoelastic responses in RH-jump experiments. The similarities and differences between RH-jump and T-jump conditions are also presented. In addition, the difficulties in modeling the combined effects of temperature and relative humidity changes that result from these differences are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2107–2121, 2004     

Corrosion studies of polyaniline/coconut oil poly(esteramide urethane) coatings

Advancements in the area of conducting polymers have been towards their application as effective corrosion protective coatings to replace the use of heavy metals as additives in the coatings industries, which are now considered to be an environmental as well as health hazard. With the aim to utilize a sustainable resource based polymer for the development of an anti‐corrosive conducting coating material, coconut oil based conducting blend coatings of polyaniline and poly(esteramide urethane) were prepared by loading different ratios (2, 4 and 8 wt%) of polyaniline in poly(esteramide urethane). Then their physico‐chemical, thermal, morphological, conductivity and anti‐corrosive coating characteristics were investigated. The effect of a 2 year environmental aging process on the coated samples was analyzed by thermal methods as well as by corrosion studies. Results showed that the corrosion protective performance of the blend coatings was far superior than that of plane poly(esteramide urethane). These coatings showed enhanced corrosion protection in acid as well as alkaline environments upto 360 and 192 hr respectively. Conductivity of the blends was found to be in the range 2.5 × 10^?5–5.7 × 10^?4 S/cm^?1. An increase in the thermal stability of the blend coatings and a decrease in their conductivity was noticed in the aged samples which was attributed to the crosslinking effect. The corrosion protective performance of the coatings remained almost unaffected even after 2 years of aging. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of multivalent cations,temperature, and aging on SOM thermal properties

Multivalent cations are suggested to influence the supramolecular structure of soil organic matter (SOM) via inter- and intra-molecular interactions with SOM functional groups. In this study, we tested the combined effect of cations, temperature treatment, and isothermal aging on SOM matrix properties. Samples from a peat and a mineral soil were either enriched with Na, Ca, and Al or desalinated in batch experiments. After treatment at 25, 40, 60, and 105 °C and after different periods of aging at 19 °C and 31 % relative humidity, we investigated the physicochemical matrix stability and the thermal stability against combustion. We hypothesized that multivalent cations stabilize the SOM matrix, that these structures disrupt at elevated temperatures, and that aging leads to an increase in matrix stability. The results show that cation-specific effects on matrix rigidity started to evolve in the peat only after 8 weeks of aging and were significantly lower than the temperature effects. Temperature treatment above 40 °C caused a non (or not immediately) reversible loss of water molecule bridges (WaMB) and above 60 °C a partly reversible melting process probably of semi-crystalline poly(methylene). Thermal stability increased with increasing cation valence and degree of protonation and was much less affected by temperature. Generally, Na-treated and control samples revealed lower thermal stability and lower increase in matrix rigidity with aging than those treated with Ca, Al, and H. We conclude that drying at elevated temperatures (>40 °C) may irreversibly change SOM structure via disruption of labile cross-links and melting of semi-crystalline domains.     

Catalysts and temperature driven melt polycondensation reaction for helical poly(ester‐urethane)s based on natural L‐amino acids

Catalyst and temperature driven melt polycondensation reaction was developed for natural L‐amino acid monomers to produce new classes of poly(ester‐urethane)s. Wide ranges of catalysts from alkali, alkali earth metal, transition metal and lanthanides were developed for the condensation of amino acid monomers with diols to yield poly(ester‐urethane)s. A‐B Diblock and A‐B‐A triblock species were obtained by carefully choosing mono‐ or diols in model reactions. More than two dozens of transition metal and lanthanide catalysts were identified for the polycondensation to yield high molecular weight poly(ester‐urethane)s. Theoretical studies revealed that the carbonyl carbon in ester possessed low electron density compared to the carbonyl carbon in urethane which driven the thermo‐selective polymerization process. Optical purity of the L‐amino acid residues in the melt polycondensation process was investigated using D‐ and L‐isomers and the resultant products were analyzed by chiral‐HPLC and CD spectroscopy. CD analysis revealed that the amino acid based polymers were self‐assembled as β‐sheet and polyproline type II secondary structures. Electron and atomic force microscopic analysis confirmed the formation of helical nano‐fibrous morphology in poly(ester‐urethane)s. The newly developed melt polycondensation process is very efficient and optimized for wide range of catalysts to produce diverse polymer structures from natural L‐amino acids. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1065–1077     

Enhanced biocompatibility in biostable poly(carbonate)urethane

In this work, we synthesized two MDI-based polyurethanes, including a poly(ether)urethane (PEU) and a poly(carbonate)urethane (PCU), by using different soft segments, poly(tetramethylene oxide) and poly(hexyl, ethyl)carbonate diol (M approximately 2,000). We demonstrated that, in addition to the enhanced biostability of PCU over PEU, the biological performances of PCU in vitro were also improved in general. These included, better cellular attachment and proliferation, less platelet activation, as well as reduced monocyte activation. The unusual wide-ranging enhancement in biocompatibility for PCU was believed to be related to the larger micro-phase separation in PCU (approximately 25 nm) that caused distinct protein adsorption on the surface. The total number of adherent monocytes (nonactivated and activated) on the bare sample surfaces, albumin pre-adsorbed sample surfaces, and fibrinogen pre-adsorbed sample surfaces.     

Optically transparent superhydrophobic TEOS-derived silica films by surface silylation method

Optically transparent silica films were prepared at room temperature (~27°C) by keeping the molar ratio of TEOS:MeOH:H₂O (0.001 M NH₄F) constant at 1:19.29:6.20, respectively. A surface chemical modification of the films was done with alkylchlorosilanes at different concentrations from 0 to 1 vol. % and aging times varied from half to 2 h. The DMCS and TMCS surface modified silica films showed the static water contact angle of 146° and 162°, respectively. When the DMCS and TMCS modified films were cured at temperatures higher than 240 and 275°C, respectively, the films became superhydrophilic. Further, the humidity study was carried out at a relative humidity of 90% at 30°C temperature over 60 days. We characterized the water repellent silica films by Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, % of optical transmission, humidity tests and contact angle measurements.     

Thermodynamics of dimethylene urethane and poly(dimethylene urethane) in the range from T → 0 to 490 K at standard pressure

By high-precision dynamic calorimetry the temperature dependences of heat capacity of dimethylene urethane (DMU) between 320 and 370 K and partially crystalline poly(dimethylene urethane) (PDMU) in the range 326-490 K at standard pressure have been determined within ±1.5%. The thermodynamic characteristics of fusion of the substances, namely the temperature interval of melting, temperature, enthalpy and entropy of fusion, as well as the characteristics of devitrification and glassy state for poly(dimethylene urethane) have been estimated. The first and the second cryoscopic constants have been calculated for dimethylene urethane. The experimental data obtained in the present work and literature findings on the heat capacity of the substances were used to calculate their thermodynamic functions: the heat capacity C°_p (T), enthalpy H°(T)−H°(0), entropy S°(T) and Gibbs function G°(T)−H°(0) over the range from T→0 to (370-480) K. Based on the data, the thermodynamic characteristics of polymerization process with five-membered ring opening Δ_polH°, Δ_polS° and Δ_polG° of dimethylene urethane with the formation of linear partially crystalline poly(dimethylene urethane) have been evaluated.     

Novel silver/polyurethane nanocomposite by in situ reduction: Effects of the silver nanoparticles on phase and viscoelastic behavior

A novel silver/poly(carbonate urethane) nanocomposite was prepared through in situ reduction of a silver salt (AgNO₃) added to a solution consisting of a commercial poly(carbonate urethane) dissolved in N,N‐dimethylformamide (DMF). In this system, the presence of the poly(carbonate urethane) was proved to protect the silver nanoparticles, whose formation was confirmed by means of UV–vis spectroscopy, from aggregation phenomena. The silver morphology developed in the solid state after DMF casting was imaged by FESEM. Homogeneous dispersion of silver nanoprisms in the poly(carbonate urethane) matrix was clearly observed. The effects of dispersion of silver nanoparticles within the poly(carbonate urethane) matrix were investigated by means of ATR‐FTIR and multifrequency dynamic mechanical thermal analyses. The obtained results revealed that the presence of silver nanoparticles modifies both the phase and the viscoelastic behaviors of poly(carbonate urethane). As a matter of fact, the hydrogen bond formation in the hard and soft segments was found to be hindered and the molecular motions of the soft segments were restricted, because a comparatively higher activation energy was required for the related α‐relaxation process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 344–350, 2008     

Poly(urethane-oxazolidone): Synthesis, characterisation and shape memory properties

Poly(urethane-oxazolidone) were synthesized by reacting isocyanate-terminated oxazolidone with hydroxy-telechelic poly(tetramethylene oxide) (PTMO). The molar ratios of the reactants were varied to get polymers of varying oxazolidone and urethane compositons. The polymers were characterized by DSC, FTIR, XRD, dynamic mechanical thermal analysis and chemical analyses. An increase in the concentration of urethane and oxazolidone groups caused a decrease in tensile strength and elongation of the poly(urethane-oxazolidone). The polymers possessed crystallites of PTMO whose melting transition temperature decreased on enhancing the oxazolidone concentration. The polymers exhibited thermo-responsive shape memory properties, which was confirmed and quantified by cyclic tensile tests. The influence of oxazolidone modification and the consequent soft/hard segment variation on the thermal, mechanical, dynamic-mechanical and shape recovery properties of the resultant polymers was investigated. The oxazolidone moities conferred enhanced shape recovery and shape fixity to the polyurethane.     

Preparation of Reinforced poly (BisGMA-UDMA) Graphene-Based Nanocomposites Via Moderate in Situ SET-LRP

In the present study, cross-linked poly (dimethacrylate- urethane dimethacrylate) [poly (BisGMA-UDMA)] functionalized-graphene oxide nanosheets were prepared via single-electron transfer living radical polymerization (SET-LRP) using the ‘grafting from’ strategy, under mild conditions. This method first involves the covalent attachment of Br-containing groups onto the surface of grapheme sheets to give the initiating-groups-containing graphene (G-Br). After that, the succeeding SET-LRP polymerization in DMSO in the presence of a Cu wire/Me₆TREN catalytic system at room temperature leads to the grafting of poly (BisGMA-UDMA) chains onto the graphene surface. The resulting graphene-poly (dimethacrylate- urethane dimethacrylate) (G-PDMA-UDMA) nanocomposites were characterized using FT-IR, XRD, DSC, AFM, FE-SEM, and TEM analysis techniques. It was proved that polymer chains were successfully introduced to the surface of the graphene planes. After grafting with poly (BisGMA-UDMA), the dispersibility of the modified GO sheets significantly improved. When compared to G-PDMA, the resulting G-PDMA-UDMA nanocomposite revealed around 75%, 97%, and 65%, increase in compressive strength, Young's modulus and toughness, respectively. Such smart graphene-based nanocomposites can be used as promising biomaterials in orthopaedic and dental applications with the desired mechanical properties.     

Blends of a siloxane/urea/urethane-segmented copolymer with an IPDI-based polyetherurethane

A series of copolymer blends have been prepared using a poly(ether urethane) and a poly(siloxane–urea–urethane). The copolymers were prepared by a hardsegment first, two-step polymerization method. The hard segments of the copolymers were derived from isophorone diisocyanate (IP) and 1,4-benzenedimethanol (B), and the soft segments were based on polytetrahydrofuran (PTMO, M_w = 2000), and polydimethylsiloxane (PDMS, M_w =27,000), respectively. The siloxanecontaining copolymer, PDMS27K-IP-B2 (2 moles diol chain extender/mole PDMS27K), was used as the minor component (1.6, 2.5 and 6.0 wt%) in a series of blends. These blends were found to preserve the mechanical properties of the poly(ether–urethane) as well as the surface properties of the poly(siloxane–urea–urethane).     

Physical aging in amorphous poly(ethylene furanoate): Enthalpic recovery,density, and oxygen transport considerations

The current work utilizes three separate techniques to study the physical aging process in amorphous poly(ethylene furanoate) (PEF), which is a recently introduced engineering thermoplastic with enhanced properties compared to petroleum‐sourced poly(ethylene terephthalate). Differential scanning calorimetry aging experiments were conducted at multiple aging temperatures and times, and the resultant enthalpic recovery values compared to the theoretical maximum enthalpy loss evaluated from calculations involving extrapolation of the equilibrium liquid line. Density measurements reveal densification of the matrix for the aged versus unaged samples, and provide an estimate for the reduction in free volume for the aged samples. Complementary oxygen permeation and pressure‐decay sorption experiments provide independent verification of the free volume reduction mechanism for physical aging in glassy polymers. The current work provides the first detailed aging study for PEF. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 389–399     

Synthesis and properties of novel segmented polyurethanes containing alkyl phosphatidylcholine side groups

In this article, we report the synthesis and properties of novel segmented polyurethanes containing alkyl phosphatidylcholine side groups. Alkyl phosphatidylcholine groups were attached to the hard blocks of the polyurethanes. A novel diol, 9-(2-hydroxy-1-hydroxymethyl-1-methyl-ethylcarbamoyl)-nonyl-phosphatidylcholine (HDEAPC), was synthesized and characterized by FTIR, ¹H-NMR and mass spectroscopy. Two types of polyurethanes, poly(ether urethane)s and poly(carbonate urethane)s, containing alkyl phosphatidylcholine side groups were synthesized using methylenebis(phenylene isocyanate) (MDI), polytetramethyleneoxide (PTMO), poly(1,6-hexyl-1,5-pentylcarbonate) diol (PHPCD), 1,4-butanediol (BDO) and HDEAPC. The obtained phosphatidylcholine polyurethanes had relatively high molecular weights and good mechanical strength, as characterized by GPC and Instron. XPS and contact angle studies revealed that there was enrichment of alkyl phosphatidylcholine side groups near the surface of the polyurethanes. Biocompatibility was evaluated by protein adsorption using conventional polyurethanes as references. The surface of phosphatidylcholine poly(carbonate urethane)s effectively suppressed protein adsorption.     

The investigation on the effect of surface radiation oxidation of bamboo fiber‐filled PMMA composite

The aim of this investigation was to study the effect of surface thermal oxidation of bamboo/poly(methyl methacrylate) composite by irradiation. Thermal oxidative effects on the surface energy of bamboo fiber were measured by radiation as a function of exposure time and temperature. Oxidized bamboo/poly(methyl methacrylate), after exposure to air at temperatures of 100°C and 110°C, had a range of maximum surface energies from 38 to 41 mJ/m². Comparisons between Fourier transform infrared carbonyl peak growth and the surface energy showed that both methods detect oxidation, though the increase in surface energy was detected before the carbonyl peak growth was noticeable. The work of adhesion predicted by the surface free energies obtained in this work between a coated calcium carbonate and bamboo fiber changes by 10% due to the oxidation of the polymer at 110°C. The structural results were discussed in the oxidation chemistry of the macromolecule.