Effects of Poly(Propylene Oxide)–Poly(Ethylene Oxide)–Poly(Propylene Oxide) Triblock Copolymer on the Gelation of Poly(Ethylene Oxide)–Poly(Propylene Oxide)–Poly(Ethylene Oxide) Aqueous Solutions

Poly(ethylene oxide)-poly(propylene oxide)–poly(ethylene oxide) ((EO)_n–(PO)_m–(EO)_n) block copolymers, commercially available as Pluronics (BASF Corp.) and Poloxamers (ICI Corp.), have been widely applied in medicine, biochemistry, and other fields because of their ability to form reversible micelles and physical gels in aqueous solution. Generally, for PEO–PPO–PEO block copolymers with higher ethylene oxide concentration, the micellization and gelation in aqueous solution are easier. However, if we introduce the reverse block copolymer PPO–PEO–PPO into PEO–PPO–PEO aqueous solutions, the micellization and gelation of the system will be more complex. In this work, the reverse block copolymer PO₁₄–EO₂₄–PO₁₄ (17R4) was added to the Pluronics EO₂₀–PO₇₀–EO₂₀ (P123), EO₁₀₀–PO₆₅–EO₁₀₀ (F127), and EO₁₃₃–PO₅₀–EO₁₃₃ (F108) aqueous solutions with different molar ratios. The rheological properties of different mixtures were measured to study the additive effect on the gelation behavior. The sol–gel transition temperature of the P123, F127, and F108 solutions shifted to a higher temperature when 17R4 was added to the solutions. In addition, the existence of 17R4 greatly affected the stability of gels. These results help to better understand the gelation of Pluronic aqueous solutions.     

Micromechanical Behavior and Glass Transition Temperature of Poly(Methyl Methacrylate)–Rubber Blends

Abstract

The microhardness of transparent rubber‐toughened poly(methyl methacrylate) (RTPMMA) was investigated by means of the microindentation technique. Core‐shell particles (CSP) with a rubbery shell were used as reinforcing material for the production of RTPMMA. The increasing volume fraction of CSP within the poly(methyl methacrylate) (PMMA) matrix is shown to soften the material, diminishing the hardness (H) value of RTPMMA of about 40% of the initial value at 35 vol% CSP content. Creep experiments under the indenter are reported. The creep constant is found to increase by adding CSP up to a leveling‐off value. On the other hand, the thermal variation of the creep constant for the blends shows a maximum. Results reveal a good correlation of the glass transition temperature (T _g) value deduced from microindentation, and the values obtained from differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques. Contrary to expectation H is shown to decrease with increasing glass transition temperature. In the case of the drawn materials, the indentation anisotropy is shown to gradually increase with draw ratio and CSP content. This finding is explained on the basis of the higher orientation of the PMMA molecules near the periphery of CSP.     

Hydrogen Bonding Interactions in Miscible Blends of Poly(hydroxyether ester)s with Poly(N‐vinyl pyrrolidone)

Studies on the miscibility and intermolecular specific interactions in the blends of two structurally similar poly(hydroxyether ester)s, poly(hydroxyether terephthalate ester) (PHETE), and poly(hydroxyether benzoate) (PHEB) with poly(4‐vinyl pyrrolidone) (PVPy) are reported. In the miscible blends there are intermolecular specific interactions between PHEEs and PVPy. It was found that intercomponent hydrogen‐bonding interactions in PHETE/PVPy blends are much stronger than those in PHEB/PVPy blends. It seems that the higher ratio of hydroxyl to carbonyl groups results in the stronger intermolecular hydrogen bonding interactions. The difference in intermolecular specific interactions between the two miscible systems is interpreted on the basis of the impact of macromolecular structures on intermolecular specific interactions. The structural characteristics of macromolecular chains, such as chain connectivity, accessibility (or screening effect), and rigidity of the macromolecular chains have a profound effect on the intermolecular interactions. These factors constitute steric hindrance and reduce the specific interactions among functional groups. These factors can become dominant in the blends of polymers.     

Effects of Molecular Weight on Thermal Degradation of Poly(α-methyl styrene) in Nitrogen

The effects of molecular weight on the thermal degradation behavior of poly(α-methyl styrene) (PAMS) was investigated by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) and thermogravimetric analysis (TGA). The Py-GC/MS analysis results showed that the degradation of PAMS with different molecular weights in nitrogen produced only the monomer, alpha-methylstyrene. The TGA results showed a pronounced reduction in the decomposition temperature with increasing molecular weight. The degradation kinetic parameters, calculated by the Kissinger and the Coats–Redfern methods, further revealed that the activation energy and the pre-exponential factor decreased with increasing molecular weight. Most importantly, the degradation order of the PAMS in nitrogen remained around 1, independent of the molecular weight, suggesting the maintenance of the depolymerization mechanism. All the above results provided an insight into the effects of molecular weight on the thermal degradation behavior of PAMS.     

A Study on Properties of Poly(vinyl chloride)/Poly(α-methylstyrene-acrylonitrile) Binary Blends

Blends of poly(vinyl chloride) (PVC) and poly(α-methylstyrene-acrylonitrile) (α-MSAN) with variable composition of 0 to 100 wt% were prepared by melt mixing. Properties of binary blends were extensively studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), heat distortion temperature (HDT), mechanical properties, melt flow rate (MFR), and scanning electron microscope (SEM). A single glass transition temperature (T_g ) was observed by DSC and DMTA, indicating miscibility between PVC and α-MSAN. The results of ATR-FTIR indicated that specific strong interactions were not present in the blends and the miscibility was due to interaction between –CN and PVC. With increasing amount of α-MSAN, considerable increase occurred in HDT, flexural strength, and flexural modulus compared with reverse s-shaped decrease in impact strength and elongation at break. Synergism was observed in tensile strength and MFR. No phase separation was observed in SEM photographs, indicating miscibility between PVC and α-MSAN. In addition, morphology of the impact-fractured surfaces, including roughness and non-fused particles, correlated well with the mechanical properties and MFR.     

Nanostructured Thermosetting Blends of Phenolic Thermosets and Poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) Triblock Copolymer

The amphiphilic triblock copolymer, poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) (PEO‐b‐PPO‐b‐PEO) was incorporated into novolac resin to prepare thermosetting blends. The morphology of the thermosetting blends was investigated by means of atomic force microscopy (AFM) and small‐angle x‐ray scattering (SAXS) and the nanostructures were obtained. It was identified that the reaction‐induced phase separation occurred in the blends of phenolic thermosets with the model poly(propylene oxide) (PPO), whereas poly(ethylene oxide) (PEO) was miscible with novolac resin after and before the curing reaction. In terms of miscibility and phase behavior of the subchains of the triblock copolymer with novolac resin, it was demonstrated that the formation of nanostructures in the thermosets followed a mechanism of reaction‐induced microphase separation.     

Study of Miscibility in Polymer Blends Obtained from Binary Inclusion Complexes of γ-Cyclodextrin and Polycarbonate/Poly(Ethylene Terephthalate)

In this work the synthesis and characterization of the nanostructure of polymer blends of polycarbonate (PC) and poly(ethylene terephthalate) (PET) obtained from their inclusion complexes with γ-cyclodextrin are reported. The blends prepared by this method present differences in their miscibility compared with those blends obtained by conventional methods like solution casting, coprecipitation, or melt blending. In order to understand the influence of molecular weight in the inclusion complex process, PCs of M_w = 64,000 and 28,000 g/mol were used. The analysis of the nanostructured blend by Fourier transform infrared (FTIR), ¹H-nuclear magnetic resonance (¹H-NMR), wide-angle X-ray diffraction (WAXD), differential scanning colorimetry (DSC), and thermogravimetric analysis (TGA) suggests the existence of specific intermolecular interactions between PC and PET that promote miscibility in this normally immiscible polymer blend. Studies by FTIR confirm that the miscibility found was not due to a transesterification reaction during DSC analysis. There were also differences in the morphology of the blends, observed by optical microscopy, obtaining a more homogeneous phase for blends formed in inclusion complexes. The results obtained strongly suggest an improvement in miscibility of the PC/PET blends.     

Shear Effect on Morphology of Poly(Butylene Terephthalate)/Poly(Styrene‐co‐Acrylonitrile) Blends

Abstract

The shear flow effect on the morphology of poly(butylene terephthalate)(PBT)/poly(styrene‐co‐acrylonitrile)(SAN) was studied by a parallel plate type shear apparatus. In PBT/SAN = 20/80 blend, particle size of dispersed domains was governed by both break‐up and coalescence processes, and it was much affected by shear rate. The minimum particle size was observed at a certain shear rate. This phenomenon can be explained by the shear matching effect of PBT and SAN; that is, the viscosity ratio of PBT to SAN changed with shear rate and the finest morphology was obtained at the appropriate viscosity ratio. Similar behavior was also observed for PBT/SAN = 70/30 (PBT was the matrix), even though the particle size was larger than that of PBT/SAN = 20/80. For PBT/SAN = 10/90 blend, the sample showed a complicated appearance during shearing. A translucent region correlated to the fine morphology was observed more than twice with increasing shear rate. This phenomenon could not be explained by the viscosity matching effect only. It was affected by small changes in the balance of breaking‐up and coalescence effects.     

Maleic Acid–alt–Styrene Copolymer as Compatibilizer for Poly(Ethylene Oxide)-Poly(Styrene)Blends

Maleic acid-alt-styrene (MAaS) copolymer with number-average molecular weight [Mbar] _n = 2500 was used as a compatibilizer in blends of poly(ethylene oxide) (PEO) and poly(styrene) (PS). PEO with weight-average molecular weight [Mbar] _w = 10⁵ (PEO₁₀₀) and two PS samples with [Mbar] _w = 9 × 10⁴ and 4 × 10⁵, respectively (PS₉₀ and PS₄₀₀, respectively) were used. A depression of the melting temperature T _m of PEO in blends containing MAaS relative to pure PEO and PEO/PS blends was observed. The melting enthalpy ΔH _m for the PEO/PS blends containing MAaS was lower than those of pure PEO and PEO/PS blends without compatibilizer. The crystallization kinetics of PEO and the blends were studied by differential scanning calorimetry (DSC) at different crystallization temperatures T _c. Flory-Huggins interaction parameters χ₁₂ for the blends were estimated. Their values are in good agreement with those obtained for similar systems and suggest that the free energy of mixing ΔG _mix should be negative. Polarized optical microscopy shows differences in the macroscopic homogeneity of the blends containing compatibilizer that could be attributed to a compatibilization process.     

Preparation and Characterization of Gelatin–Poly(L-lactic) Acid/Poly(hydroxybutyrate-co-hydroxyvalerate) Composite Nanofibrous Scaffolds

Poly(L-lactic) acid (PLLA) scaffolds, prepared by electrospinning technology, have been suggested for use in tissue engineering. They remain a challenge for application in biological fields due to PLLA's slow degradation and hydrophobic nature. We describe PLLA, PLLA/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and PLLA/PHBV/gelatin (Gt) composite nanofiberous scaffolds (Gt–PLLA/PHBV) electrospun by changing the electrospinning technology. The morphologies and hydrophilicity of these fibers were characterized by scanning electron microscopy (SEM) and water contact angle measurement. The results showed that the addition of PHBV and Gt resulted in a decrease in the diameters and their distribution and greatly improved the hydrophilicity. The in-vitro degradation test indicated that GT–PLLA/PHBV composite scaffolds exhibited a faster degradation rate than PLLA and PLLA/PHBV scaffolds. Dermal fibroblasts viabilities on nanofibrous scaffolds were characterized by [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] (MTT) assay and cell morphologies after 7 days culture. Results indicated that the GT–PLLA/PHBV composite nanofibers showed the highest bioactivity among the three scaffolds and increased with increasing time. The SEM images of cells/scaffolds composite materials showed the GT–PLLA/PHBV composite nanofibers enhanced the dermal fibroblasts's adhesion, proliferation, and spreading. It is suggested that the nanofibrous composite scaffolds of GT–PLLA/PHBV composites would be a promising candidate for tissue engineering scaffolds.     

Poly(3,4-ethylene dioxythiophene): Poly(styrene sulfonate)的共振拉曼光谱研究

通过拉曼光谱方法分别对PEDOT:PSS掺杂和去掺杂状态进行了详细分析. 实验结果表明, 去掺杂的PEDOT:PSS由于其在激发波长附近的吸收增强而引起了共振效应, 拉曼信号得到大幅度增强, 可见, 以633 nm(He-Ne)激光为激发波长的拉曼光谱是研究PEDOT:PSS掺杂状态的有效方法. 此外, 显微拉曼光谱也是分析聚合物发光二极管器件内各层材料的有效手段.     

Toughening of Poly (Butylene Terephthalate) with Epoxy-Filled Poly (Ethylene–Octene) Copolymer

Toughened poly (butylene terephthalate) (PBT) with triglycidyl isocyanurate (TGIC)-filled poly (ethylene–octene) (POE) was prepared by melt reaction extrusion. For retarding the reaction extent between PBT and the epoxy component, the TGIC was first blended with POE to enwrap its reactive epoxy groups. Then, the TGIC-filled POE was used to melt blend with PBT. The Fourier transform infrared (FTIR) spectra showed that no other peaks appeared in the POE/TGIC specimens except for those originally existing in pure POE and TGIC. The rheological results further confirmed that no reaction occurred between the epoxy and the POE matrix. When the POE/TGIC was blended with PBT, a distinct increase of the viscosity suggested that the migration of the TGIC from POE to PBT during the melt processing induced chain extension reactions of PBT. The results obtained from DSC and DMA revealed that the chain extension of PBT induced by the reaction with TGIC restricted the mobility of PBT chains leading to a limitation of the recrystallization-remelting process and an increase of the glass transition temperature of PBT. The mechanical tests showed that the presence of TGIC in the POE phase distinctly improved the toughness of PBT. Compared to the case of a PBT/POE (80/20, wt%/wt%) blend, the elongation at break and impact strength of the system filled with 5 phr TGIC were increased more than three and six times, respectively.     

Effect of the amounts of glycidyl methacrylate on the mechanical and dynamic properties of styrene–butadiene–glycidyl methacrylate terpolymer/silica composites

GMA-SBRs with GMA contents in the range of 0.06–0.71 wt.% were synthesized and used to evaluate the properties of the silica composites for fuel-efficient tires. The chemical structures of the GMA-SBRs were analyzed using Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance (¹H NMR), size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). GMA-SBRs can enhance filler–rubber interaction through covalent bond formation between the silica filler and rubber molecules. After compounding, the cure characteristics and mechanical and dynamic properties of the GMA-SBR silica-filled composites were analyzed. The mechanical properties, including the Mooney viscosity, bound rubber, swelling ratio, and moduli, exhibited obvious differences with increasing GMA content. However, the optimum content of GMA in the GMA-SBR, in terms of dynamic properties such as the Payne effect which represents the change in dynamic modulus against the strain to determine the extent of filler flocculation and tan δ at 60 °C representing tire rolling resistance, was ~0.6 wt.%. These results are due to improved silica dispersion, resulting from increased covalent bond formation between GMA-SBR and the silica surface. This approach assists in the determination of functional group contents in functionalized emulsion styrene–butadiene rubber for fuel-efficient tires, leading to a decrease in vehicular greenhouse gas emission.     

Effect of Poly(butyl acrylate)-g-poly(styrene-co-acrylonitrile)’s Core/shell Ratio on Mechanical and Thermal Properties of Poly(butyl acrylate)-g-poly(styrene-co-acrylonitrile)/α-methylstyrene-acrylonitrile Binary Blends

Poly(butyl acrylate)-g-poly(styrene-co-acrylonitrile) terpolymer (PBA-g-SAN) with different core/shell ratios and α-methylstyrene-acrylonitrile (α-MSAN) were mixed via melt blending (25/75, W/W). It was found that the core/shell ratio of PBA-g-SAN played an important role in the toughening of rigid α-MSAN. According to an analysis of the impact strength and the morphologies of the impact fractured surfaces, the optimum core/shell ratio with the highest toughening efficiency was 60/40. Considering the results of dynamic mechanical thermal analysis (DMTA), the blends retained the high glass transition temperature (T_g) of α-MSAN because of the immiscibility between the two components. Moreover, increasing the core/shell ratio did not result in sacrificing the heat distortion temperature of the blends, which was attributed to the almost unchanged high temperature T_g of α-MSAN. The tensile strength, flexural strength, and modulus declined slightly with the increasing core content of PBA-g-SAN, which suggested that the stiffness of the blends decreased with the increasing core/shell ratio. This study showed that 60/40 was the optimum core/shell ratio used for toughening modification; it achieved a good balance between mechanical and heat resistance performance.     

Properties of Poly(butylene terephthalate)/Bisphenol A Polycarbonate Blends Toughening with Epoxy-Functionalized Acrylonitrile–Butadiene–Styrene Particles

Glycidyl methacylate functionalized acrylonitrile–butadiene–styrene particles (ABS-g-GMA) prepared via an emulsion polymerization method were used to toughen poly(butylene terephthalate) (PBT)/bisphenol A polycarbonate (PC) blends. DMA results showed PBT was partially miscible with PC and the addition of ABS-g-GMA improved the miscibility between PBT and PC. DSC tests further testified that the introduction of ABS-g-GMA improved the miscibility of PBT and PC according to the T_m depression criterion. SEM displayed a very good dispersion of ABS-g-GMA particles in the PBT/PC blends and the dispersed phase size of PC decreased due to the compatibilization effect of ABS-g-GMA. The mechanical properties showed that the addition of 10 wt% ABS-g-GMA was sufficient to induce a super-tough fracture behavior to the PBT/PC blends and a notched impact strength of more than 1000J/m was achieved. The Vu-Khanh test showed that stable crack propagation took place for PBT/PC blends with the addition of ABS-g-GMA and led to ductile failure.     

Polypropylene/Poly (Trimethylene Terephthalate)–Blend Fibers

Polypropylene (PP)/polyester (PES)–blend fibers were prepared by extruder melt spinning. The polymer blend consisted of PP and a “master batch” (MB) based on polytrimethylene terephthalate (PTT) or polyethylene terephthalate (PET), binary PTT/PET or PP/PTT blends, and also on a ternary PP/(PTT/PET) blend. The phase structure of PP/PES–blend fibers was examined. PES microfibers showed separation from the PP matrix in blend fibers. The impact of MB composition and rheological characteristics on phase structure parameters indicate a significant contribution of the PTT in the binary MB on the length of dispersed PES microfibers in the PP matrix. However, the blends of PP and ternary MB (PP/PTT/PET) have a lower diameter and length of the PES microfibers. The presence of PTT/PET (PES) enhances the structural and mechanical properties of the blend PP/PES fibers. In addition, PTT increases the tensile strength of the PP/PES–blend fibers if a binary MB is used, while the fiber nonuniformity is reduced in the presence of a ternary MB.     

Action–Angle Variables in a Particular Case of the Restricted Three-Body Problem

Doklady Physics - The restricted problem of three bodies (material points) moving under the action of Newtonian gravitational attraction is considered. The masses of the main attracting points are...     

Study on Fractal Character of High Impact Polystyrene with Poly(cis‐butadiene) Rubber Partly Miscible Blends by Fractal Measure Relations and Box‐Counting Methods

Abstract

Phase formation and evolution of high‐impact polystyrene/poly(cis‐butadiene) rubber (HIPS/PcBR) blends during melting and mixing processes were investigated by scanning electron micrographs analysis. The diameter, d _p , was used to describe the evolution of the phase morphology of HIPS/PcBR blends during mixing. Scale functions, S _N (r) and S _M (r), were defined to confirm the self‐similarity of the phase morphology. The plots of S _N (r)/S _N (r) _m [the maximum of S _N (r)] vs. r/r _m (the maximum of r) and S _M (r)/S _M (r) _m [the maximum of S _M (r)] vs. r/r _m showed the phase morphology had self‐similarity. Furthermore, the fractal dimension, D, of different HIPS/PcBR blends was calculated by two different methods (fractal measure relations and box‐counting methods). The results showed that the fractal dimension was an effective parameter for study of the phase morphology of polymer blends.     

Poly(acrylamide‐co‐acrylic acid)/Poly(vinyl pyrrolidone) Polymer Blends Prepared by Dispersion Polymerization

The structure and properties of a three‐component system, a poly(acrylamide‐co‐acrylic acid)/poly(vinyl pyrrolidone) [P(AM‐co‐AA)/PVP] polymer blend prepared by dispersion polymerization, were studied. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the resulting P(AM‐co‐AA) microspheres with diameters between 200–300 nm were well‐dispersed in the PVP matrix. Fourier transform infrared spectra (FTIR) showed that intermolecular hydrogen bonding interaction occurred between the dispersed phase and the continuous phase. The mechanical properties of P(AM‐co‐AA)/PVP polymer blends were also determined. With different mass ratios of acrylamide to acrylic acid, it was found that the blends had better mechanical properties with increased AA content.