Preparation of microporous polymers in the form of particles and a thin film from hyperbranched polyphenylenes

The use of a hyperbranched polymer as a building block for the synthesis of a microporous organic polymer was demonstrated. Hyperbranched polyphenylenes (HBPs) were prepared from (3,5‐dibromophenyl)boronic acid, which contained numerous unreacted bromophenyl end groups. Utilizing metal‐catalyzed coupling reactions between these functional groups, cross‐linked porous polymers were obtained. Although the HBPs did not show porosity, their cross‐linked polymers had highly porous structures with Brunauer–Emmett–Teller surface areas of up to 2030 m²/g. An insoluble porous thin film was fabricated by spin casting of a solution containing a HBP followed by Sonogashira cross‐coupling reaction. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2336–2342     

Utilization of Moiré interferometry to study strain transfer across polymer interfaces within multilayer thermoplastic elastomers

In this paper, a moiré interferometry technique was used to study the viscoelastic strain distributions within and across the interfaces of multilayer thermoplastic elastomers, which were fabricated as models for functionally modulus‐graded materials. Two types of interfaces, those formed from miscible and immiscible pairs of the same thickness, were fabricated within multilayer thermoplastic samples. The analysis of the moiré fringe patterns indicated that there was a large normal strain, ε_y, concentration at the polymer interfaces formed from the immiscible or partially miscible pairs. However, this large normal strain was not observed at the interfaces formed from the miscible pairs. These results suggest that the magnitude of strain concentrations at polymer interfaces within functionally modulus‐graded materials could be significantly reduced by extensive chain interdiffusion, which could be promoted by careful selection of miscible polymer pairs. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2196–2206, 2005     

Time-dependent behaviors of a FGPM hollow sphere under the coupling of multi-fields

This paper presents an analytical solution for time-dependent behaviors of a hollow sphere made of functionally graded piezoelectric material (FGPM) under the coupling of multi-fields. Material properties, electric parameters, permeability, thermal conductivity and creep parameters vary smoothly through the radial direction of the FGPM spherical structure according to a simple power-law. Using equations of equilibrium, stress–strain and strain-displacement in a differential equation, containing creep strains, for displacement are obtained. Firstly, ignoring creep strains in the differential equation, a closed form solution for the initial electromagnetothermoelastic stresses at zero time is presented, and considering Von Mises stress balance equation, the effective electromagnetothermoelastic stresses are also presented. Secondly, considering only creep strains, creep stress rates are obtained by using the Prandtl–Reuss equations and Norton’s law. Finally, time-dependent creep stress redistributions at any time t_i are obtained iteratively. The aim of this research is to understand the effects of the graded index on creep behavior of hollow spherical structures and design optimum FGPM hollow spherical structures.     

Effects of graded porous structure on local strain distribution under compression in silicone rubber

Silicone rubber samples with gradually changing pore sizes within the range of 70–610 μm are produced using an improved spacer method. The samples are scanned using an X‐ray computed tomography to evaluate their graded structure as compared to uniform rubber. A compressive test reveals that graded porous silicone rubber has characteristic stress–strain curves whose slope changes within a specific strain range depending on the porous structure. Analysis results of local strain based on a digital image correlation of the graded porous silicone rubber under compression demonstrate that the characteristic stress–strain properties are caused by shifts in the main deformation region in the graded structure. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1033–1042     

Tailoring poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) microstructure and physicochemical properties by exploring its binary phase diagram with dimethylformamide

Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (PVDF‐CTFE) membranes were prepared by solvent casting from dimethylformamide (DMF). The preparation conditions involved a systematic variation of polymer/solvent ratio and solvent evaporation temperature. The microstructural variations of the PVDF‐CTFE membranes depend on the different regions of the PVDF‐CTFE/DMF phase diagram, explained by the Flory‐Huggins theory. The effect of the polymer/solvent ratio and solvent evaporation temperature on the morphology, degree of porosity, β phase content, degree of crystallinity, mechanical, dielectric, and piezoelectric properties of the PVDF‐CTFE polymer were evaluated. In this binary system, the porous microstructure is attributed to a spinodal decomposition of the liquid‐liquid phase separation. For a given polymer/solvent ratio, 20 wt % , and higher evaporation solvent temperature, the β phase content is around 82% and the piezoelectric coefficient, d₃₃, is ? 4 pC/N © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 761–773     

Pore size modification of macroporous crosslinked poly(dicyclopentadiene)

This article describes the pore size modification and in situ surface functionalization of macroporous crosslinked poly(dicyclopentadiene), produced by chemically induced phase separation, with norbornene‐functionalized poly(ethylene glycol) telechelic oligomers. The microstructure of the open porosity materials produced with this technique consisted of agglomerated particles. The incorporation of these telechelic oligomers allowed a substantial decrease in the pore size and a related increase in the internal surface area. These functionalized oligomers acted as stabilizers around the primary particles produced by phase separation and blocked their growth so that the materials resulting from the agglomeration of these smaller particles showed finer microstructures. The resulting porous materials were characterized by scanning electron microscopy, density measurements, nitrogen adsorption, and mercury porosimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2036–2046, 2003     

液相渗硅法制备多孔Si/SiC生物形态陶瓷

榉木经高温热解转化为碳模板,通过液相渗硅反应（LSIP）,在1550℃,1.5h渗硅,1700℃排硅制备了保持木材微观结构的多孔Si/SiC陶瓷。利用X-射线衍射分析（XRD）, 扫描电子显微镜（SEM）,压汞技术对样品的物相构成、显微结构和孔径分布进行了分析,利用阿基米德法和三点弯曲法测定了多孔陶瓷的显气孔率、密度和弯曲强度。结果表明,最终产物由主晶相β-SiC和少量的Si组成;控制高温排硅时间可以得到孔隙率为16％~32％的多孔Si/SiC陶瓷,可调控其产物的相组成和力学性能。对LSIP工艺的反应机理进行了探讨。     

Strength and elasticity of bimodal porous silica prepared from water glass

The bending strength and the Young’s modulus of bimodal porous silica gels having different porosity were evaluated. The porosity of the gel increased by aging the gel under basic conditions, and decreased with increasing the calcination temperature. The mesopores disappeared on calcination at 1,050 °C, whereas continuous macropores retained their morphology up to 1,050 °C for all the samples. Both the bending strength and the Young’s modulus of the bimodal porous silica gels were expressed as power-law functions of the bulk density, and no effect of bimodal pore structures on mechanical properties was observed. We also found linear correlation between the bending strength and the elasticity. The bimodal porous silica had higher strength and elastic modulus compared with other porous materials at the same porosity probably due to the presence of homogeneous micrometer-scale macropores.     

Viscoelastic characterization of polymers using instrumented indentation. I. Quasi‐static testing*

The use of instrumented indentation to characterize the mechanical response of polymeric materials was studied. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for the creep compliance and stress relaxation modulus for two glassy polymeric materials, epoxy and poly(methyl methacrylate), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison with the indentation stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than the rheometry values. Additional study of the deformation remaining in epoxy after indentation creep testing as a function of the creep hold time revealed that a large portion of the creep displacement measured was due to postyield flow. Indentation creep measurements of the epoxy with a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the unfilled PDMS were mainly linear elastic, with the filled PDMS exhibiting some time‐dependent and slight nonlinear responses in both rheometry and indentation measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1794–1811, 2005     

Phase assembly-induced transition of three dimensional nanofibril- to sheet-networks in porous cellulose with tunable properties

Ultralight and highly porous cellulose was fabricated via cellulose/sodium hydroxide/urea aqueous solution followed by gelation, coagulation and freeze-drying in the current work. The water content and freeze rate of cellulose coagulated sample are two crucial factors controlling the morphology, density and porosity of porous cellulose, which led to an interesting morphological transition from three dimensional nanofibrillar network to sheet network in porous cellulose. It was proposed that the aggregation and assembly of cellulose-rich phase and crystallization of water-rich phase were closely related to this transition. Based on this concept, a series of cellulose materials with densities varied from 0.129 to 0.330 g cm^?3 and corresponding porosities ranged from 91.4 to 78.0 %, were obtained. The porous celluloses showed a good ductility (strain to fracture is more than 30 %) and high modulus, which also could be tuned by porous morphology. The new understanding on the morphological transition in porous cellulose could be beneficial for the development of “green” porous materials.     

Microcellular processing and relaxation of poly(ether ether ketone)

The semicrystalline microcellular closed‐cell foams are prepared by a two‐stage batch foaming process from poly(ether ether ketone) and characterized by scanning electronic microscopy. It can be observed that there are two kinds of cells with obviously different cellular sizes in the same transect and the distribution of larger cells (about 7 μm) looks like sandwich. The effects of foaming temperatures and transfer times on the cellular sizes and cell densities of porous materials were discussed. Particular emphasis was given to the effects of crystalline on the microcellular morphology. The relaxation mechanism of microcellular materials was systemically investigated by dynamic mechanics analysis. A plain on the storage modulus curve before T_g was observed due to the densification of cells. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2890–2898, 2007     

Evidence of mechanisms occurring in thermally induced phase separation of polymeric systems

Thermally induced phase separation is a fabrication technique for porous polymeric structures. By means of easy‐to‐tune processing parameters, such as system composition and demixing temperature, a vast latitude of average pore dimensions, pore size distributions, and morphologies can be obtained. The relation between demixing temperature and morphology was demonstrated via cloud point curve measurement and foams fabrication with controlled thermal protocols, for the model system poly‐l ‐lactide–dioxane–water. The morphologies obtained at a temperature lower than cloud point showed a closed‐pore architecture, suggesting a “nucleation‐and‐growth” separation mechanism, which produced larger pores at higher holding times. Conversely, the porous structures attained when holding the sample above the cloud point exhibited open pores with dimensions independent of time, denoting a phase separation occurring during sample freezing. Finally, the influence of the cooling rate on final morphology was investigated, showing a clear correlation with microstructure and pore size. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 979–983     

Tensile creep of thermoplastics: Time‐strain superposition of non‐iso free‐volume data

The dimensional stability of thermoplastics is characterized by their tensile compliance D(t,σ,T) as a function of time t, stress σ, and temperature T. Creep retardation times are controlled by the free volume available for underlying molecular (segmental) motions. Tensile deformation of polymeric materials, whose Poisson ratio is smaller than 0.5, is accompanied by volume dilatation that can be identified with an increase in available free volume. Consequently, a steady increase in strain with time during tensile creep experiments accounts for shortening of the retardation times. The superposition of as‐received tensile compliance curves is difficult because any point of a curve requires a shift factor along the time axis that differs from those of other points. In this article, tensile creep at a constant stress and temperature is viewed as a non‐iso free‐volume process. A procedure is proposed to transform as‐received data to a pseudo‐iso free‐volume state that eliminates this deficiency and permits construction of a generalized compliance curve for the pseudo‐iso free‐volume state. This curve can be used for calculation of real‐time‐dependent compliance for any selected stress in the range of reversible deformations. As the superposed curve can be generated with several short‐term creep tests (e.g., 100 min) for a series of stresses, the proposed procedure saves experimental time. The effects of physical aging on tensile compliance (observed previously by other researchers) are interpreted in terms of the proposed approach in appendix A . © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 736–748, 2003     

Brownian dynamics simulation of two‐dimensional nanosheets under biaxial extensional flow

The morphology dynamics of two‐dimensional nanosheets under extensional flow are investigated using a coarse‐grained model. Nanosheets (graphene, BNNS, MX₂) are promising materials for a variety of materials and electronics applications. Extensional flow fields are often present during dispersion processing, such as spin coating. Both nanosheet properties (e.g., moduli, size) and processing parameters (e.g., extension rate) can have a significant impact on the nanosheet morphology and thus, the structure and properties of the bulk material. Our previously developed dimensionless Brownian dynamics methodology is used to explore biaxial extensional flow. Nanosheets exhibit a flat conformation under extensional flow for high bending moduli and an extended “washrag” conformation for low bending moduli. Intrinsic extensional viscosity increases with strain before reaching a plateau. The intrinsic viscosity exhibits a weak power law with nanosheet molecular weight. These simulation results allow for experimental control over morphology as a function of nanosheet properties and flow type and strength. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1247–1253     

High temperature creep behavior of phosphoric acid‐polybenzimidazole gel membranes

This work investigates the effects of polymer solids content and macromolecular structure on the high temperature creep behavior of polybenzimidazole (PBI) gel membranes imbibed with phosphoric acid (PA) after preparation via a polyphosphoric acid (PPA) mediated sol‐gel process Low‐solids, highly acid‐doped PBI membranes demonstrate outstanding fuel cell performance under anhydrous, ambient pressure, and high temperature (120–200 °C) operating conditions. However, PBI membranes are susceptible to creep under compressive loads at elevated temperatures, so their long‐term mechanical durability is a major concern. Here, we report results for the creep behavior of PBI membranes subject to compression at 180 °C. For para‐ and meta‐PBI homopolymers, increasing polymer solids content results in lower creep compliance and higher extensional viscosity, which may be rationalized by increasing chain density in the sol‐gel network. Comparing various homo‐ and copolymers at similar solids loading, differences in creep behavior may be rationalized in terms of chain–chain and chain‐solvent interactions that control macromolecular solubility and stiffness in the PA solvent. The results demonstrate the feasibility of improving the mechanical properties of PA‐doped PBI membranes by control of polymer solids content and rational design of PBI macromolecular structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1527–1538     

有机泡沫浸渍法制备多孔磷灰石-硅灰石(AW)生物活性玻璃陶瓷研究

0引言多孔磷灰石-硅灰石(apatite-wollastonite glass ceramic,AW-GC)生物活性玻璃陶瓷,具有良好的生物活性、骨透导性和一定的可降解性,近年在骨组织工程研究中倍受重视[1￣4]。理想的骨组织修复和支架材料应具备三维立体多孔结构,这种结构有利于细胞粘附增殖、细胞外基质沉积、营养和氧气进入及代谢产物排出,也有利于血管和神经长入[5]。     

Influence of multiwall carbon nanotubes on morphology and electrical conductivity of PP/ABS blends

Polypropylene (PP) and acrylonitrile‐butadiene‐styrene (ABS) blends with multiwall carbon nanotubes (MWNT) were prepared by melt mixing. PP/ABS blends without MWNT revealed coarse co continuous structures on varying the ABS content from 40 to 70 wt %. Bulk electrical conductivity of the blends showed lower percolation threshold (0.4–0.5 wt %) in the 45/55 co continuous blends whereas the percolation threshold was between 2 and 3 wt % in matrix‐particle dispersed morphology of 80/20 blends. Interestingly, droplet size was observed to decrease with addition of MWNT above percolation threshold in 80/20 blends. Further, the bulk electrical conductivity was found to be dependent on the melt flow index of PP. The non‐polar or weakly polar nature of blends constituents resulted in the temperature independent dielectric constant, dielectric loss, and DC electrical conductivity. Rheological analysis revealed the formation of 3D network‐like structure in 80/20 PP/ABS blends at 3 wt % MWNT. An attempt was made to understand the relationship between rheology, morphology, and electrical conductivity of these blends. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2286–2295, 2008     

Interfacial stability of compatibilizers dictated by the thermodynamic interactions in an immiscible system and the effects of micelles on the crystallization of PLLA

Poly(L-lactic acid) (PLLA) is blended with three acrylonitrile-butadiene-styrene (ABS) materials and compatibilized by a kind of poly(methyl methacrylate) (PMMA)-type reactive comb (RC) polymer (RC). The compatibilization efficiency is found to be dictated by the thermodynamic interactions between PMMA-type compatibilizers and ABS materials. For one type of ABS, which is composed of methyl methacrylate (MMA), styrene (St), acrylonitrile (AN), and butadiene (BD), the MMA component of ABS is able to strengthen the interaction between the PMMA-type compatibilizers and the ABS phase and thus the obtained compatibilized PLLA/ABS blends display a fine cocontinuous morphology and excellent mechanical properties. For the other two ABS materials, which are constituted by St, AN, and BD, it has been found that the PMMA-type compatibilizers are pulled out from the interface to form micelles in the PLLA phase, on account of the weakening interactions between ABS and PMMA-type compatibilizers. The thus formed micelles can interact with the crystallization of PLLA and the melting temperature (T_m) of PLLA is split into a lower and a higher peak firstly, compared to the T_m of neat PLLA, then significantly decrease to lower temperature, with increasing the amount of micelles in the PLLA phase. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 372–382     

Fabrication of highly porous starch monoliths and their application as green desiccants

Starch monoliths with oriented porous structures were developed from starches and glycerin as a plasticizer using unidirectional freeze‐drying technology. The morphology of the porous starch monoliths made from different starches was determined by scanning electron microscopy (SEM), and the porosity, mechanical properties and moisture absorption of the porous materials were evaluated. The results show that porous starch monoliths made from oxidized starch with 15% glycerin had good mechanical strength with the best moisture absorption. Increasing the starch concentration significantly improved their strength and increased the moisture absorption rate as well. The moisture absorption of the porous monolith made from oxidized starch is comparable with commonly used desiccants. The porous starch monoliths can successfully remove water from 95% ethanol to produce absolute ethanol due to their selective absorption for water. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrogel‐coated polyurethane/urea shape memory polymer foams

Shape memory polymers (SMPs) are a class of responsive polymers that have attracted attention in designing biomedical devices because of their potential to improve minimally invasive surgeries. Use of porous SMPs in vascular grafts has been proposed because porosity aids in transfer of fluids through the graft and growth of vascular tissue. However, porosity also allows blood to leak through grafts so preclotting the materials is necessary. Here hydrogels have been synthesized from acrylic acid and N‐hydroxyethyl acrylamide and coated around a porous SMP produced from lactose functionalized polyurea‐urethanes. The biocompatibility of the polymers used to prepare the cross‐linked shape memory material is demonstrated using an in vitro cell assay. As expected, the hydrogel coating enhanced fluid uptake abilities without hindering the shape memory properties. These results indicate that hydrogels can be used in porous SMP materials without inhibiting the shape recovery of the material. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1389–1395