Thermo‐responsive polyurethane hydrogels based on poly(ethylene glycol) and poly(caprolactone): Physico‐chemical and mechanical properties

In this work, we present the synthesis and characterization of chemically crosslinked polyurethanes (PU) composed of poly(ethylene glycol) (PEG) and poly(caprolactone) diol (PCL‐diol), as hydrophilic and hydrophobic segments respectively, poly(caprolactone) triol (PCL‐triol), to induce hydrolysable crosslinks, and hexamethylene diisocyanate (HDI). The syntheses were performed at 45 °C, resulting in polyurethanes with different PEG/PCL‐diol/PCL‐triol mass fractions. All the PUs are able to crystallize and their thermal properties depend on the global composition. The water uptake capacities of the PU increase as the PEG amount increases. The water into hydrogels is present in different environments, as bounded, bulk and free water. The PU hydrogels are thermo‐responsive, presenting a negative dependence of the water uptake with the temperature for PEG rich networks, which gradually changes to a positive behavior as the amount of poly(caprolactone) (PCL) segments increases. However, the water uptake capacity changes continuously without an abrupt transition. Scanning electron microscopy (SEM) analyses of the hydrogel morphology after lyophilization revealed a porous structure. Mechanical compression tests revealed that the hydrogels present good resilience and low recovery hysteresis when they are subject to cycles of compression–decompression. In addition, the mechanical properties of the hydrogels varies with the composition and crosslinking density, and therefore with the water uptake capacity. The PU properties can be tuned to fit for different applications, such as biomedical applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43573.     

Polyurethanes based on 2,2‐Dinitropropane‐1,3‐diol and 2,2‐bis(azidomethyl)propane‐1,3‐diol as potential energetic binders

On the base of 2,2‐bis(azidomethyl)propane‐1,3‐diol (BAMP) and 2,2‐dinitropropane‐1,3‐diol (DNPD) four different polyurethanes were synthesized in a polyaddition reaction using hexamethylene diisocyanate (HMDI) and diisocyanato ethane (DIE). The obtained prepolymers were mainly characterized using vibrational spectroscopy (IR) and elemental analysis. For determination of low and high temperature behavior, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used. Investigations concerning friction and impact sensitivities were carried out using a BAM drop hammer and friction tester. The energetic properties of the polymers were determined using bomb calorimetric measurements and calculated with the EXPLO5 V6.02 computer code. The obtained values were compared with the glycidyl azide polymer (GAP). The compounds turned out to be insensitive toward friction (>360 N) and less sensitive toward impact (40 J). The good physical stabilities, along with their sufficient thermal stability (170–210 °C) and moderate energetic properties renders these polymers into potential compounds for applications as binders in energetic formul;ations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43991.     

Polyurethane/poly(ethylene‐co‐ethyl acrylate) and functional carbon black‐based hybrids: Physical properties and shape memory behavior

A polyurethane (PU) was developed from poly(dimethylamine‐co‐epichlorohydrin‐co‐ethylenediamine) (PDMAE) and polyethylene glycol (PEG) as soft segment and 2,4‐toluene diisocyanate (TDI) incorporating as hard segment. Later PU was blended with poly(ethylene‐co‐ethyl acrylate) (PEEA). Poly(vinyl alcohol)‐functionalized carbon black (CB‐PVA) nanoparticles was used as filler. The structure, morphology, mechanical, crystallization, and shape memory behavior (heat and voltage) were investigated methodically. Due to physical interaction of the blend components, unique self‐assembled network morphology was observed. The interpenetrating network was responsible for 83% rise in tensile modulus and 46% increase in Young's modulus of PU/PEEA/CB‐PVA 1 hybrid compared with neat PU/PEEA bend. Electrical conductivity was increased to 0.2 Scm^?1 with 1 wt % CB‐PVA nanofiller. The original shape of sample was almost 94% recovered using heat induced shape memory effect while 97% recovery was observed in an electric field of 40 V. Electroactive shape memory results were found better than heat stimulation effect. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43481.     

Carbon nanotubes‐filled thermoplastic polyurethane–urea and carboxylated acrylonitrile butadiene rubber blend nanocomposites

This article reports the preparation and characterization of multiwalled carbon nanotubes (MWCNTs)‐filled thermoplastic polyurethane–urea (TPUU) and carboxylated acrylonitrile butadiene rubber (XNBR) blend nanocomposites. The dispersion of the MWCNTs was carried out using a laboratory two roll mill. Three different loadings, that is, 1, 3, and 5 wt % of the MWCNTs were used. The electron microscopy image analysis proves that the MWCNTs are evenly dispersed along the shear flow direction. Through incorporation of the nanotubes in the blend, the tensile modulus was increased from 9.90 ± 0.5 to 45.30 ± 0.3 MPa, and the tensile strength at break was increased from 25.4 ± 2.5 to 33.0 ± 1.5 MPa. The wide angle X‐ray scattering result showed that the TPUU:XNBR blends were arranged in layered structures. These structures are formed through chemical reactions of ? NH group from urethane and urea with the carboxylic group on XNBR. Furthermore, even at a very low loading, the high degree of nanotubes dispersion results in a significant increase in the electrical percolation threshold. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40341.     

Synthesis of high solid content waterborne polyurethanes with controllable bimodal particle size distribution

A series of waterborne polyurethane dispersions were synthesized by one‐pot reaction and step‐wise reaction, respectively. The effects of synthetic methods and DMPA content on the particle size distribution (PSD), solid contents and viscosity were studied by laser particle size analyzer, Brookfield viscometer and TEM analysis. High solid content and low viscosity waterborne polyurethanes (WPUs) with controllable bimodal PSD were prepared by one‐pot reaction using 2,2‐dimethylol propionic acid (DMPA) as the only self‐emulsifier. Meanwhile, 40% solid content WPUs with unimodal PSD were obtained by step‐wise reaction at the same formula. With the increment of DMPA content, the ratio of large particles to small particles decreased and two peaks of the particle size finally became one peak by one‐pot reaction while the PSD remained unimodal by step‐wise reaction. The reason leading to the difference of PSD between one‐pot reaction and step‐wise reaction was analyzed and the relationships among PSD, viscosity and solid content were discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40420.     

Synthesis and characterization of polyhydroxylated polybutadiene binding 2,2′‐thiobis(4‐methyl‐6‐tert‐butylphenol) with isophorone diisocyanate

A macromolecular hindered phenol antioxidant, polyhydroxylated polybutadiene containing thioether binding 2,2′‐thiobis(4‐methyl‐6‐tert‐butylphenol) (PHPBT‐b‐TPH), was synthesized via a two‐step nucleophilic addition reaction using isophorone diisocyanate (IPDI) as linkage. First, the ? OH groups of PHPBT reacted with secondary ? NCO groups of IPDI to form the adduct PHPBT‐NCO, then the PHPBT‐b‐TPH was obtained by one phenolic ? OH of 2,2′‐thiobis(4‐methyl‐6‐tert‐butylphenol) (TPH) reacting with the PHPBT‐NCO. The PHPBT‐b‐TPH was characterized by Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance (¹H‐NMR), ¹³C‐NMR, and thermogravimetric analysis, and its antioxidant activity in natural rubber was studied by an accelerated aging test. Influences of reaction conditions on the two nucleophilic reactions between ? OH group and ? NCO group were investigated. In addition, catalytic mechanism for the reaction between PHPBT‐NCO and TPH was discussed. The results showed that the adduct PHPBT‐NCO could be obtained by using dibutyltin dilaurate (DBTDL) as catalyst, and the suitable temperature and DBTDL amount were 35°C and 3 wt %, respectively. However, triethylamine (TEA) was more efficient than DBTDL to catalyze the reaction between PHPBT‐NCO and TPH because of steric hindrance effect. In addition, it was found that the thermal stability and antioxidant activity of PHPBT‐b‐TPH were higher than those of the low molecular weight antioxidant TPH. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40942.     

Electrospun polyvinyl alcohol/waterborne polyurethane composite nanofibers involving cellulose nanofibers

TEMPO‐oxidized cellulose nanofibers (TOCNs) were used as nanofillers in this work. Composite nanofibers of polyvinyl alcohol (PVA)/waterborne polyurethane (WPU) reinforced with TOCNs were produced by electrospinning. The reinforcing capability of TOCNs was investigated by tensile tests. Scanning electron microscopy (SEM), X‐ray diffraction, and thermogravimetry analyses were also carried out in order to characterize the appearance, crystallinity, and reinforcing effect of the cellulose nanofibers. SEM results showed that PVA/WPU/TOCNs composite nanofibers presented a highly homogeneous dispersion of TOCNs. The reinforced composites had about 44% increase in their mechanical properties with addition of only 5 wt % of TOCNs while about 42% decrease in elongation at break. The TOCNs reinforced composite nanofibers were more thermally stable than pure PVA/WPU nanofibers. The development of crystalline structure in the composite fibers was observed by XRD. Since PVA, WPU, and TOCNs are hydrophilic, non‐toxic, and biocompatible, and therefore, these nanocomposite nanofibers could be used for tissue scaffolding, filtration materials, and medical industries as wound dressing materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41051.     

Silk‐inspired polyurethane containing glyalaglyala tetrapeptide. III. morphological,thermal, and mechanical features of electrosprayed and electrospun deposition

Morphological, thermal, and mechanical features of electrosprayed and electrospun deposition of the silk‐inspired polyurethane (PU) containing GlycineAlanineGlycineAlanine (GlyAlaGlyAla, the featured peptide sequence of silkworm silk fibroin) tetrapeptide, which was synthesized by the traditional liquid‐phase peptide synthesis method and the classical two‐step polymerization method using Boc‐protected amino acids and diisocyanates as starting materials, were characterized. The results show that the synthesized silk‐inspired PU dissolved in tetrahydrofuran (THF) can be easily electrosprayed or electrospun into the film form, although its molecular weight ranging from 13,000 to 15,000 is quite low. Elastomeric fibrous membranes with surface morphologies of “droplets,” “bead‐on‐string,” and “nonwoven fibers” have been obtained by electrospraying and electrospinning the silk‐inspired PU/THF solution of varying concentrations. The thermograms confirm high thermostability of the silk‐inspired PU between 350 and 400°C due to the polar peptide linkages. The tanδ peak of dynamic mechanical analysis curve corresponding to its glass transition temperatures is detected at ?34.3°C. Its elongation at break is about 140–150%, and the breaking tensile strength ranges from 22 to 27 MPa, which is consistent with the data of other PUs containing l ‐alanine residue. Information provided by this study can be used to better understand the correlation between the natural and man‐made silk polymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40245.     

Drug‐loaded polyurethane/clay nanocomposite nanofibers for topical drug‐delivery application

In this study, polyurethane/nanoclay nanocomposite nanofibrous webs were prepared by electrospinning. An antiseptic drug, chlorhexidine acetate (CA), was loaded onto montmorillonite clay and was then incorporated into polyurethane nanofibers. For comparison, the CA drug was loaded directly into the polyurethane solution dope used to electrospin the nanofibers. The emphasis was on investigating the effect of the drug loading into the nanoclay vis‐à‐vis direct drug loading on the drug‐release behavior of nanofibrous webs. The nanofibrous webs were also evaluated for other properties, such as moisture vapor transmission, porosity determination, contact angle measurement, and antibacterial activity, which are important for topical drug‐delivery application. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40230.     

聚氨酯硬泡隔热保温材料在通信工程中应用

本文以包头市通信管道工程为例,阐述了聚氨酯硬泡隔热保温材料在跨河桁架管道中的作用、施工方法以及应用前景。