Flexible Molecular Chains Research Articles

Tailoring new bisphenol a ethoxylated shape memory polyurethanes

AbstractShape memory polyurethanes (SMPUs) have generated great attention because of their unique properties. These properties are result of a particular molecular structure consisting of flexible molecular chains with low glass transition temperatures alternating with hard urethane segments. In this field, bisphenol A (BA) has been used for a long time as chain extender due to the good properties of the obtained SPMU materials. Nevertheless, the high toxicity of this compound has caused a high decrease on its use. For this reason, it has been selected a lower toxicity compound, bisphenol A ethoxylate (BAE). In this work, it is described a new SMPUs based on BAE and the influence of the hard segment on the thermo‐mechanical properties and shape memory capacity. For that, both the proportion of the components and the diisocyanate employed (2,4‐toluene diisocyanate (TDI), 4,4′‐methylene bis(phenylisocyanate) (MDI) or a TDI/MDI mixture) have been modified. Then, depending on the molecular architecture achieved, the polyurethanes present different properties, which were studied by different techniques, such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic‐mechanical thermal analysis (DMTA). It has been observed that glass transition temperature (Tg) increases as the hard phase content in the PU samples increases. In addition, Tg‐MDI > Tg‐MDI‐TDI > Tg‐TDI, so it is possible to control the Tg of the material, that is, shape memory transition temperature varying the diisocyanate. Finally, the shape memory capacity of the PUs was evaluated by thermo‐mechanical analysis (TMA). All the synthesized PUs have shown good shape memory effect with fixation ratios up to 80% and recovery ratios close to 100%.

Separation of dimethyl carbonate/methanol azeotropic mixture by pervaporation with dealcoholized room temperature-vulcanized silicone rubber/nanosilica hybrid active layer

Less pollution, low toxicity, high binding force, dealcoholization-type, room temperature-vulcanized (RTV) silicone rubber and alkyl-modified nanosilica were applied to obtain a nano SiO2/RTV pervaporation (PV) hybrid active layer. The layer is applied to the PV membrane separation technology of dimethyl carbonate (DMC)/methanol azeotrope given its flexible molecular chain and its structure that is conducive to the transmission of DMC. The nanoSiO2/RTV active layer was characterized by reflection infrared spectroscopy, X-ray diffraction, thermogravimetry, and swelling analyses. The PV membrane was characterized by scanning electron microscopy and contact angle measurement. The permeation flux, separation factor, swelling/diffusion selectivity, and activation energy of the hybrid membrane were evaluated by PV test. Results showed that the alkyl-modified nanosilica reduced the order of RTV and the contact angle with the azeotrope, facilitated the preferential infiltration of DMC, and increased the permeation flux of DMC during PV. The separation factor increased first and then decreased with increasing amount of alkyl nanosilica. This finding could be due to the following: the alkyl group on the surface of nanosilica has DMC selection ability, the excessively high content of nanosilica causes the free volume of the active layer to increase, and methanol can penetrate quickly. NanoSiO2/RTV hybrid membrane M−30 possessed a permeation flux of 3.8 kg/m2h at 50 °C and a separation factor of 4.42; whereas M−15 had a separation factor of 5.60 at 30 °C and a permeation flux of 1.2 kg/m2h. It is preferentially separated from DMC compared with the results reported in literature. The overall separation efficiency reached a new height.

Triply Biobased Thermoplastic Composites of Polylactide/Succinylated Lignin/Epoxidized Soybean Oil

Soybean oil is beneficial to improve the compatibility between polylactide (PLA) and succinylated lignin (SAL), which leads to the preparation of a host of biobased composites containing PLA, SAL, and epoxidized soybean oil (ESO). The introduction of SAL and ESO enables the relatively homogeneous morphology and slightly better miscibility obtained from triply PLA/SAL/ESO composites after dynamic vulcanization compared with unmodified PLA. The rigidity of the composites is found to decline gradually due to the addition of flexible molecular chains. According to the reaction between SAL and ESO, the Tg of PLA/SAL/ESO composites is susceptible to the movement of flexible molecular chains. The rheological behaviors of PLA/SAL/ESO under different conditions, i.e., temperature and frequency, exhibit a competition between viscidity and elasticity. The thermal stability of the composites displays a slight decrease due to the degradation of SAL and then the deterioration of ESO. The elongation at break and notched impact strength of the composites with augmentation of ESO increase by 12% and 0.5 kJ/m2, respectively. The triply biobased PLA/SAL/ESO composite is thus deemed as a bio-renewable and environmentally friendly product that may find vast applications.

Improving the compatibility of cold-mixed epoxy asphalt based on the epoxidized soybean oil

Cold-mixed epoxy asphalt (CEA) has been used for paving steel bridges and high-grade roads because of its properties superiority and environmental protection. In order to obtain CEA with excellent performance, it is a significant mean to improve the compatibility between asphalt and epoxy resin (ER) by introducing epoxidized soybean oil (ESO). The viscosity and glass transition temperature (Tg) decrease, and the asphalt dispersed more uniformly in the ER with increasing ESO concentration. Based on the dynamic mechanical analysis, the CEA-ESO30 shows only one Tg and excellent compatibility between asphalt and ER. The elongation at break and storage modulus of CEA-ESO was higher than CEA, indicating that the flexible ESO molecular chain in the curing networks might improve the stiffness of CEA-ESO. The FTIR spectra exhibited that the ESO reacted with the curing agent to form 3D networks with ER, which may result in good compatibility between asphalt and ER.

A 3D polyacrylonitrile nanofiber and flexible polydimethylsiloxane macromolecule combined all-solid-state composite electrolyte for efficient lithium metal batteries.

All-solid-state polymer electrolytes have received widespread attention due to their superior safety over liquid electrolytes that are prone to leaks. However, poor ionic conductivity and uncontrollable lithium dendrite growth have greatly limited the rapid development of polymer electrolytes. Hence, we report a composite polymer electrolyte combining a polyacrylonitrile (PAN) electrospun fiber membrane, flexible polydimethylsiloxane (PDMS) macromolecules and a polyethylene oxide (PEO) polymer. The introduction of PDMS with a highly flexible molecular chain, ultra-low glass transition energy and high free volume can help optimize lithium ion migration paths and improve the interface compatibility between the electrolyte and the electrode. In addition, the nano-network structure of the PAN nanofiber membrane can promote the interaction between adjacent polymer molecular chains and improve the mechanical properties of the composite electrolyte to suppress the lithium dendrite growth. The synergistic effect of the PDMS and PAN electrospun nanofiber membranes endows the composite electrolyte with superior ionic conductivity and excellent electrochemical stability towards lithium metal. The interface impedance of the Li/Li symmetric battery with the composite electrolyte after 15 days of continuous standing has no significant change compared with the initial state, and the battery can maintain stable cycling for 1200 h without short circuit under a dynamic current of 0.3 mA cm-2. The obtained composite polymer electrolyte has potential application prospects in the field of high-energy lithium metal batteries.

Structure and Properties of Aromatic Polyimide Fibers Fabricated by a Novel “Reaction-Spinning” Method

In this work, two sets of high performance polyimide (PI) fibers fabricated by a more environmentally-friendly and highly efficient “reaction-spinning” method were firstly reported. The relationship between the spinning rate, chemical structure and the imidization degree of the PI precursor fibers were investigated, and the results indicated a moderate low spinning speed and relatively flexible molecular chains are both favorable for the partial imidization reaction in the spinning process. 2D WAXD results demonstrate that the rigid PDA-based PI fibers possess a higher alignment of polymer chains along the fiber axis during the spinning compared to the flexible ODA-based PIs, resulting in enhanced mechanical properties, with the tensile strength of 1.2-2.8 GPa and modulus of 53.6-111.2 GPa, respectively. Meanwhile, ODA sets of PI fibers exhibit a higher loop strength and knot strength than the commercial Aramid and PBO fibers. The process used in this study has a significant potential for realizing industrial level production of high strength and high modulus PI fibers. Open image in new window

Lossless Fast Drop Self‐Transport on Anisotropic Omniphobic Surfaces: Origin and Elimination of Microscopic Liquid Residue

Surfaces enabling directional drop self-transport have exceptional applications in digital microfluidics, chemical analysis, bioassay, and microreactor technology. While such properties have been obtained by engineering a surface with anisotropic microstructures, a microscopic liquid residue-though it might be invisible macroscopically-is generally left behind the transported drop, resulting in undesired transport loss and severely limiting practical applications of the surface. Here, the origin of microscopic liquid residue is studied by investigating directional drop self-transport on anisotropic surfaces made of radially arranged omniphobic microstripes. It is revealed that the occurrence of a liquid residue is governed by a transport-velocity-dependent dynamic wetting mechanism involving the formation of entrained thin liquid films at high capillary numbers while the local dynamic receding contact angle vanishes. Rayleigh-like breakup of the liquid films leads to the microscopic liquid residue. It is further shown that a liquid-like coating featuring highly flexible molecular chains can effectively suppress the formation of entrained liquid films at high transport velocities, thereby facilitating lossless and fast drop self-transport on anisotropic omniphobic surfaces.

Synthesis and Properties of Branched Polymer Based on Modified Chitosan for Enhanced Oil Recovery

In this study, chitosan and polyamide-amine(PAMAM) were utilized to prepare a branched polymer based on modified chitosan (HPDCS) for enhanced oil recovery(EOR). The structure of the product was confirmed by FT-IR, 1HNMR and SEM. Compared with hydrolyzed polyacrylamide (HPAM), HPDCS exhibited better thickening properties and shear resistance due to its special branched structure and the flexible molecular chains can be deformed through the pore throat of the porous medium, which can avoid serious damage to the molecular chains. After a 45-hour reaction period with biological enzyme, the apparent viscosity of the HPDCS solution decreased significantly, and the viscosity retention rate was only 67.7%, indicating that the introduction of chitosan in the polymer could improve the biodegradability of polymers to a certain extent. Based on sandpacked tube displacement experiments, the HPDCS could build high resistance factor and residual resistance factor in the corresponding porous medium which indicated that the HPDCS performed excellent mobility control ability. Besides, compared with HPAM, the HPDCS solution of 2000 mg/L showed better oil recovery of 24.12% in the corresponding porous medium, which demonstrated that the branched polymer has a more outstanding EOR ability.

Preparation of Epoxy Shape Memory Polymers for Deployable Space Structures Using Flexible Diamines

In order to develop epoxy shape memory polymers (ESMPs) with high switching temperature and excellent toughness for deployable space structures, the crosslink density and chain flexibility of candidate ESMP samples were tunned by adding two flexible poly(oxypropylene) diamines, Jeffamine D-230 (D230) and Jeffamine D-400 (D400), as a secondary curing agent. The desired switching temperature of ESMPs for deployable space structures was set within the range of 120-135°C. By adding D230 and D400, the switching temperature of the ESMPs could be adjusted to within this range by increasing their crosslink density, and their impact strength could be significantly increased due to the stress relaxation properties of the diamines’ flexible molecular chains. The modulus and tensile strength of the ESMPs increased, but elongation at break decreased, in proportion to the diamine content. The ESMPs with a suitable switching temperature for deployable space structures had a high elongation at break greater than 22 % and good shape recovery and shape fixity ratios. The larger the value of shape recovery ratio, the faster the shape recovery speed.

Adjusting the Linear Range of Au-MOF Fluorescent Probes for Real-Time Analyzing Intracellular GSH in Living Cells.

A series of Au-loaded metal-organic frameworks (MOFs) were synthesized in this study and further employed for real-time quantitative analysis of intracellular glutathione (GSH) level. Different linear ranges can be acquired by altering the size of gold and MOF particles, or adjusting the proportion of 2-aminoterephthalic acid/1,4-benzenedicarboxylate linkers, which is also observed on fluorescein isothiocyanate-attached Au-MOFs. Further study reveals that the flexible molecular chain of GSH with the -COOH/-NH2 and -SH terminals may readily tie on relevant gold nanoparticles through its -NH2/-COOH groups, which then restricts the intramolecular motions of fluorescence probes and thus induces marked fluorescence enhancement. On the basis of these observations, the intracellular GSH levels of different cells including L02 cells, Hela, and U87 as well as HepG2 cancer cells can be rapidly evaluated by these Au-MOF probes.

Fabrication of (PPC/NCC)/PVA composites with inner-outer double constrained structure and improved glass transition temperature

Improving glass transition temperature (Tg) and mechanical property of the environment-friendly poly(propylene carbonate) via intermacromolecular complexation through hydrogen bonding is attractive and of great importance. A novel and effective strategy to prepare (polypropylene carbonate/nanocrystalline cellulose)/polyvinyl alcohol ((PPC/NCC)/PVA) composites with inner-outer double constrained structure was reported in this work. Outside the PPC phase, PVA, as a strong skeleton at microscale, could constrain the movement of PPC molecular chains by forming hydrogen bonding with PPC at the interface of PPC and PVA phases; inside the PPC phase, the rod-like NCC could restrain the flexible molecular chains of PPC at nanoscale by forming multi-hydrogen bonding with PPC. Under the synergistic effect of this novel inner-outer double constrained structure, Tg, mechanical properties and thermal stability of (PPC/NCC)/PVA composite were significantly increased, e.g. Tg of the composite researched the maximum value of 49.6 °C, respectively 15.6 °C, 5.7 °C and 4.2 °C higher than that of PPC, PPC/NCC and PPC/PVA composite.

Thermal properties of polyurethane elastomer with different flexible molecular chain based on para-phenylene diisocyanate

This work focuses on the relationship between flexibility of molecular chains and thermal properties of polyurethane elastomer (PUE), which laid the foundation of further research about how to improve thermal properties of PUE. A series of PUE samples with different flexibility of molecular chains was prepared by using 1,4-butanediol (1,4-BDO)/bisphenol-a (BPA) blends with different mole ratios including 9/1, 8/2, 7/3, 6/4 and 5/5. As comparison, PUE extended with pure 1,4-BDO and BPA was also synthesized. These samples were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), etc. The results showed that with the decrease in flexibility of molecular chains the glass transition temperature (Tg) increased and low-temperature properties became worse. Besides, all samples had a certain degree of microphase separation, and soft segments in some samples were crystallized, i.e. the decreasing flexibility of molecular chains led to the impossibility of chains tightly packing and crystalline domains forming so that the degree of microphase separation decreased and the thermal properties became worse.

A molecular dynamics study of the effect of glycosidic linkage type in the hemicellulose backbone on the molecular chain flexibility.

The macromolecular conformation of the constituent polysaccharides in lignocellulosic biomass influences their supramolecular interactions, and therefore their function in plants and their performance in technical products. The flexibility of glycosidic linkages from the backbone of hemicelluloses was studied by evaluating the conformational freedom of the φ and ψ dihedral angles using molecular dynamic simulations, additionally selected molecules were correlated with experimental data by nuclear magnetic resonance spectroscopy. Three types of β-(1→4) glycosidic linkages involving the monosaccharides (Glcp, Xylp and Manp) present in the backbone of hemicelluloses were defined. Different di- and tetrasaccharides with combinations of such sugar monomers from hemicelluloses were simulated, and free energy maps of the φ - ψ space and hydrogen-bonding patterns were obtained. The glycosidic linkage between Glc-Glc or Glc-Man (C-type) was the stiffest with mainly one probable conformation; the linkage from Man-Man or Man-Glc (M-type) was similar but with an increased probability for an alternative conformation making it more flexible, and the linkage between two Xyl-units (X-type) was the most flexible with two almost equally populated conformations. Glycosidic linkages of the same type showed essentially the same conformational space in both disaccharides and in the central region of tetrasaccharides. Different probabilities of glycosidic linkage conformations in the backbone of hemicelluloses can be directly estimated from the free energy maps, which to a large degree affect the overall macromolecular conformations of these polymers. The information gained contributes to an increased understanding of the function of hemicelluloses both in the cell wall and in technical products.

Highly toughened polylactide with epoxidized polybutadiene by in-situ reactive compatibilization

Relatively high contents of rubber are commonly required to trigger the brittle-to-ductile transition when using rubber components to toughen polylactide (PLA). However, the strength may drop remarkably after incorporation of large amount of rubber. The main motivation of the present work is to achieve a good toughness-strength balance in a PLA/rubber system with less amount of rubber phase (90/10 w/w). In this study, polybutadiene (PB) was used to toughen PLA due to the flexible molecular chains. In attempt to enhance the compatibility of PB in PLA matrix, epoxidized polybutadiene (EPB) with different epoxidation degree were prepared by an in situ peroxy-formic acid method. The compatibility, phase morphologies, mechanical properties and thermal properties of the PLA/EPB blends were investigated respectively. It was found that epoxy group of EPB showed a significant effect in enhancing compatibility between rubber phase and PLA matrix, giving rise to a remarkable decrease in the particle diameter of rubber phase. When both of the good compatibility and the appropriate particle size of the rubber phase were realized, the impact toughness of PLA/EPB blend was improved by 13 times for that of pure PLA, while the tensile strength still preserved as a level of 77% (based on the value of pure PLA). The interfacial compatibilization between PLA and EPB was achieved through the formation of graft-copolymer being a compatibilizer caused by the in-situ reaction between EPB and PLA in the melt blend process. This result proves the introduction of active groups into PLA blends to be a platform to design their performance via regulating the phase structure.

Immobilization of Papain on Flexible Magnetic Nanoparticles

Flexible magnetic nanoparticles decorated with dialdehyde starch (DAS) were developed and used as a novel enzyme support for the covalent conjugation of papain. The analyses of Fourier transform infrared (FTIR) spectroscopy confirmed the preparation of magnetic particles with flexible long molecular chains on their surfaces and conjugation of papain with the Fe3O4-DAS nanoparticles. Considering that the immobilized papain was found to exhibit better tolerance to the variations of temperature and medium pH, an advantage of easy to magnetic separation and lack of negative effect on biological activity, the kind of flexible magnetic bioconjugate support should be a good immobilized enzyme carrier, and has potential application in textile, leather, food industries.

Research on Flexural Fatigue of Fiber Bundles for Lay-Flat Hose

This paper studies the flexural fatigue performance for hose reinforcement layer fiber bundles including polyester fibers, para-aramid fiber and liquid crystal polyester fiber. Bending fatigue life and changes of three fiber bundles strength during the course of fatigue development were measured. Morphology of three fiber bundles was observed by scanning electron microscopy. From the analysis of the molecular structure of the three fibers, the Molecular chain flexibility is one of the main factors of impacting resistance to bending fatigue performance. Liquid crystal polyester fiber bundles have excellent mechanical properties and the high strength retention in bending fatigue test, which is an ideal material for the production of high-strength hose.

Novel styrene polymers functionalized with phosphorus–nitrogen containing molecules: Synthesis and properties

A phosphorus and nitrogen-containing compound with high phosphorus content, AC2NP2, was firstly synthesized by the Kabachnik–Fields reaction and followed by esterification with acryloyl chloride. The synthesized comonomer was then incorporated into different amounts of polystyrene via radical solution polymerization. The copolymers were well characterized using Fourier transform infrared (FTIR), UV/vis spectrophotometer, nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), microscale combustion calorimeter (MCC) and LOI. The results showed that the AC2NP2 was easily incorporated into the backbone of polystyrene, and the copolymers prepared have high transparency. The glass transition temperature (Tg) of the copolymers was decreased with increasing the AC2NP2 content, due to the introduction of much more flexible molecular chain. The TGA results revealed that the introduction of AC2NP2 units slightly decreased the initial decomposition temperatures, but significantly improved the thermal stability of copolymers at high temperature regions under both nitrogen and air atmosphere. Furthermore, all the copolymers exhibited much lower flammability as compared with virgin polystyrene.

A comparative study of epoxy resin cured with a linear diamine and a branched polyamine

The molecular topology of amine curing agents is expected to greatly affect the curing reaction and properties of the epoxy resins, yet the exact influence still remains little understood. Herein we find out two representative aliphatic amines: linear propanediamine (PDA) and branched N,N,N′,N′-tetra(3-aminopropyl)-1,3-propanediamine (TAPA), and use them to cure diglycidyl ether of bisphenol A (DGEBA). The curing reaction, dynamic mechanical properties, and thermal stability of DGEBA/PDA and DGEBA/TAPA are systematically investigated and compared. Differential scanning calorimetry (DSC) confirms TAPA and PDA have very close reactivity much higher than that of commercial Jeffamine T-403 with the branched molecular structure. The curing kinetic analysis shows TAPA causes the higher isothermal conversion at the lower temperature (e.g., 40°C), the autocatalysis and diffusion-associated kinetics feature the isothermal reactions, and the extended Kamal model turns out to be able to well predict the curing rate. Then, the isoconversional analysis with the Vyazovkin methods demonstrates compared to PDA, TAPA leads to the lower effective activation energy at the very beginning due to its catalytic tertiary amino groups, but the reversed trend emerges in the deep-conversion stage, especially, in the glass-transition regime, owing to its flexible aliphatic molecular chains. Furthermore, the isothermal conversion at the higher temperatures is predicted from the nonisothermal experiments. Finally, dynamic mechanical analysis (DMA) shows cured DGEBA/TAPA exhibits the higher glass- and β-relaxation temperatures and crosslink density than DGEBA/PDA, and thermogravimetric analysis (TGA) reveals TAPA-cured epoxy has the excellent thermal stability with the higher char yield.

A Novel SERS-Active Tag Based on Bimetallic Flowerlike Au-Ag Nanoparticles

Bimetallic nanoparticles have received considerable attention due to their unique optical, magnetic and other properties. Their composition, architecture, shape and size can be adjusted relatively easily in order to change their properties, which provide great potential for their diverse applications. Bimetallic Au-Ag nanoparticles are very attractive because they exhibit remarkable optical properties due to their surface plasmon resonance (SPR) absorption. In this investigation, a simple synthesis process for novel, bimetallic flowerlike Au-Ag composite nanoparticles was developed. Biocompatible folic acid-conjugated chitosan with flexible molecular chains were used as the structure-directing agent in nanoparticle synthesis. The structure and properties of Au-Ag nanoparticles were studied using a variety of analytical techniques including high resolution transmission electron microscopy. These nanoparticles contained an Au core and an Ag shell and the shape and thickness of the Ag shell could be easily controlled by varying the synthesis condition. The formation and growth of flowerlike bimetallic Au-Ag composite nanoparticles was investigated and its mechanism proposed. On the basis of flowerlike Au-Ag nanoparticles which can produce surface enhanced Raman scattering (SERS), a novel SERS tag was formed, which consisted of an Au-Ag flowerlike nanoparticle, embedded Rhodamine B (RhB, a Raman reporter molecule), and a folic acid-conjugated chitosan outer layer. This new SERS tag (RhB@Au-Ag tag) exhibited greatly increased SERS intensity of RhB and hence showed great potential for tumor cell targeting and detection.

New Anhydrous Proton Exchange Membrane for Intermediate Temperature Proton Exchange Membrane Fuel Cells

Herein, we study the preparation and characterization of a new kind of proton exchange membrane. In the proton-conducting membrane of poly(vinylidene fluoride) (PVDF)/poly(ethylene oxide) (PEO)/dodecyl benzenesulfonic acid (DBS-H), we use PEO as "proton solvent" due to its flexible molecular chain. Moreover, the electronegativity of the O atom on PEO may be used to attract protons under anhydrous conditions. The membranes are thermally stable up to 200 °C with less than 3 % mass loss. At 150 °C, without extra humidification, the proton conductivity of 60 % PVDF/22 % PEO/18 % DBS-H membrane is approximately 10 (-3) S cm(-1).