聚合物催化剂的合成及应用研究

制备了强碱型离子交换树脂和强酸型离子交换树脂过渡金属催化剂。前者对还原反应、后者对氧化反应及加成反应显示出较强的催化效果。聚合物生物碱相转移催化剂对不对称诱导反应有较好的催化作用     

A new soluble aramide with pendant phthalonitrile units and polymer property enhancement by nitrile cure reactions

A new soluble aramide with pendant phthalonitrile units was prepared, while its properties including solvent resistance and thermal properties can be enhanced by further thermal treatment around the glass transition temperatures of the polymers for an extended period of time. The cured polymers were characterized by thermogravimetric analysis, differential scanning calorimetry and FTIR techniques. Such improvement in polymer properties can be attributed to the nitrile cure reactions, indicated by the observation of the decrease in nitrile absorbance and the characteristic triazine band on the FTIR spectra.     

Chemoenzymatic synthesis of amylose-grafted polyacetylene by polymer reaction manner and its conversion into organogel with DMSO by cross-linking

This paper reports chemoenzymatic synthesis of amylose-grafted polyacetylene according to the following polymer reaction manner. At first, the amine-functionalized polyacetylene was prepared by the Rh-catalyzed copolymerization of a protected amine-substituted acetylene monomer (tert-butyl propargylcarbamate) with N-propargylethanamide, followed by deprotection process. Then, the maltooligosaccharide chains were introduced on the polyacetylene by the reaction with maltoheptaose lactone. Finally, the phosphorylase-catalyzed enzymatic polymerization from the oligosaccharides on the produced polyacetylene was performed using α-d-glucose 1-phosphate as a monomer to give the polyacetylene having amylose graft-chains. Furthermore, the cross-linking reaction of the remaining amino-groups on the amylose-grafted polyacetylene with hexamethylene diisocyanate was carried out in DMSO to give the insoluble material, which formed the organogel with DMSO. The mechanical property of the gel was evaluated by compressive stress–strain measurement.     

Semi-empirical model for polyelectrolyte intrinsic viscosity as a function of solution ionic strength and polymer molecular weight

Elements of Odijk-Skolnick-Fixman and Yamakawa-Fujii polymer solution theories have been modified to create a new model that correlates flexible coil polyion intrinsic viscosity behavior with solvent and polymer properties. A new dimensionless viscosity is derived and is successfully related to the dimensionless ratio of Debye-Hückel screening length to polyion charge spacing and the degree of polymerization. The model has been applied to intrinsic viscosity data reported in the scientific literature and to data collected in our laboratory, all using sodium chloride solutions ranging in ionic strength. Multiple molecular weight fractions of six compositionally different polyelectrolytes were used to obtain 73 intrinsic viscosity versus ionic strength data points for model analysis. Regression analysis was applied to empirically determine the relationships between the dimensionless groups. The resulting model equation was found statistically adequate in describing the entire data set.     

Development of polymer films by the coalescence of polymer particles in powdered and aqueous polymer-modified mortars

This paper evaluates and compares the coalescence of polymer particles (continuous polymer films formation) in powdered polymer-modified mortars (PPMMs) and aqueous polymer-modified mortars (APMMs). Polymer-modified mortars (PMMs) using various redispersible polymer powders (powdered cement modifiers) and polymer dispersions (aqueous cement modifiers) were prepared by varying the polymer-cement ratio (P/C) and were tested for the characterization of polymer films using a scanning electron microscope (SEM) after curing for 28 days. It is concluded from the test results that mortar constituents of unmodified mortar (UMM) are loosely joined with each other due to the absence of polymer films, thus having a structure with comparatively lower mechanical and durability characteristics. By contrast, mortar constituents in PPMMs and APMMs are compactly joined with each other due to the presence of interweaving polymer films, thereby forming a monolithic structure with improved mechanical and durability characteristics. However, the results make obvious the poor coalescence of polymer particles or development of inferior quality polymers films in PPMMs as compared to that observed in APMMs. Moreover, PPMMs show less uniform distribution of polymer films as compared to that in APMMs. Different powdered cement modifiers have different film-forming capabilities. However, such difference is hardly recognized in aqueous cement modifiers. The polymer films in PPMMs and APMMs may acquire different structures. They may appear as mesh-like, thread-like, rugged, dense or fibrous with fine or rough surfaces. Development of coherent polymer films is not well pronounced at a P/C of 5% in PPMMs, whereas sometimes coherent polymer films are observed at a P/C of 5% in APMMs. At a P/C of 10% or more, fully developed, coherent polymer films are observed in both PPMMs and APMMs.     

Processing of Cf/SiC composites by hot pressing using polymer binders followed by polymer impregnation and pyrolysis

Continuous carbon fiber (C_f) reinforced silicon carbide (SiC) matrix composite (C_f/SiC) was processed through hot pressing (HP) using polycarbosilane (PCS) in matrix and polysilazane in interphase regions as polymer binders. HP experiments were conducted at 4 MPa, 1200 °C and 1 h; followed by PCS polymer impregnation and pyrolysis (PIP) at 1200 °C under vacuum. The BN/SiC-Si₃N₄ interphase formed on the C_f cloth during BN dispersed polysilazane polymer coating and pyrolysis. The influence of PCS quantity during HP experiments on C_f/SiC composites was studied. Results suggest that sintering of SiC matrix in C_f/SiC composite improves by increasing PCS content during HP; however, high PCS content increases the liquidity of SiC-PCS mixture to flow out of the composite structure. The C_f/SiC composites with relative density ranging from 79 to 83% and flexural strength from 67 to 138 MPa was achieved.     

Synthesis and photovoltaic properties of an alternating polymer based fluorene and fluorine substituted quinoxaline derivatives

An alternating polymer (PFOFTQx) with 9,9-dioctylfluorene (FO) as electron-rich unit and fluorine substituted quinoxaline (FTQx) as electron-withdrawing unit was synthesized and characterized. PFOFTQx showed similar absorption property with that of the counterpart polymer without fluorine atom (synthesized APFO-15). However, the low-lying highest occupied molecular orbit (HOMO) energy level of PFOFTQx was ?5.37 eV, about 0.07 eV smaller than that of synthesized APFO-15. In order to study the photovoltaic properties of the materials, polymer solar cells (PSCs) were fabricated with PFOFTQx as donor blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM) as acceptor. The power conversion efficiency (PCE) of PSC was 1.77% with a high open-circuit voltage (V_oc) of 0.90 V for an optimized PFOFTQx:PC₆₁BM weight ratio of 1:5, in comparison with that of synthesized APFO-15-based device (PCE of 1.60% with V_oc of 0.77 V). This study indicated that fluorine substituted quinoxaline-based polymers would be promising material with a higher V_oc for the application in polymer solar cells.     

An explicit polymer and node network model to compute micromechanical properties of silica-filled polydimethylsiloxane

Two important aspects of filled polymer systems that can influence elasticity are the random position of filler particles and the nonuniformity of polymer chain lengths that form the chain/particle network. Historically, most network elasticity models have been based on idealized assumptions of uniform chain length constrained to highly symmetric orientations. We present a novel, three-dimensional explicit polymer and node network model (EPnet) that includes both randomly distributed filler particles (nodes) and polymer lengths taken from a Gaussian distribution. The molecular level polymer forces that produce elasticity are assumed to operate between pairs of connected network nodes. The numerical model is amenable to any molecular force that depends on the distance between two nodes, however, for this paper, we assume that the polymer chain segments that connect the filler particles obey a simple two-force model, i.e. a constant force required to stretch a single polymer chain and a force arising from the binding energy between a polymer chain and a filler particle surface. Free ends, i.e. polymer segments connected to only one particle, do not contribute to the elasticity. With these assumptions, the model contains intrinsic mechanisms that appear to predict the phenomena of yield stress, tensile failure, permanent set and stress hysteresis. The model is applied to a mesoscale volume element (∼1 μm³) of silica-filled polydimethylsiloxane to study the micromechanical stress in response to various strains, e.g. tensile, compressive, shear and swell. Model predictions are in quantitative agreement with tensile stress/strain experiments.     

Decoration of multi-walled carbon nanotubes by polymer wrapping and its application in MWCNT/polyethylene composites

ABSTRACT: We dispersed the non-covalent functionalization of multi-walled carbon nanotubes (CNTs) with a polymer dispersant and obtained a powder of polymer-wrapped CNTs. The UV-vis absorption spectrum was used to investigate the optimal weight ratio of the CNTs and polymer dispersant. The powder of polymer-wrapped CNTs had improved the drawbacks of CNTs of being lightweight and difficult to process, and it can re-disperse in a solvent. Then, we blended the polymer-wrapped CNTs and polyethylene (PE) by melt-mixing and produced a conductive masterbatch and CNT/PE composites. The polymer-wrapped CNTs showed lower surface resistivity in composites than the raw CNTs. The scanning electron microscopy images also showed that the polymer-wrapped CNTs can disperse well in composites than the raw CNTs.     

氧化-还原引发法合成淀粉接枝丙烯酸高吸水性树脂

目的：研究以过硫酸铵、亚硫酸钠组成的氧化-还原引发剂“一锅法”合成淀粉接枝丙烯酸高吸水性树脂。方法：采用水溶液中引发聚合的方法。结果：在(NH4)2S2O8占0．30％，N，N’-亚甲基双丙烯酰胺占0．15％，中和度78％，引发温度40℃，丙烯酸占32％的条件下合成出有实用价值的高吸水性树脂。结论：“一锅法”简单易行，有工业价值。     

The effect of magnetic field on the oxygen reduction reaction and its application in polymer electrolyte fuel cells

The effect of magnetic field gradients on the electrochemical oxygen reduction was studied with relevance to the cathode gas reactions in polymer electrolyte fuel cells. When a permanent magnet was set behind a cathode, i.e. platinum foil or Pt-dispersed carbon paper for both electrochemical and rotating electrode experiments and oxygen was supplied to the uphill direction of the magnetic field, electrochemical flux was enhanced and the current increased with increasing the absolute value of magnetic field. This magnetic effect can be explained by the magnetic attractive force toward O₂ gas. When magnet particles were included in the catalyst layer of the cathode and the cathode was magnetized, the current of oxygen reduction was higher than that of nonmagnetized cathode. A new design of the cathode catalyst layer incorporating the magnet particles was tested, demonstrating a new method to improve the fuel cell performance.     

Preparation and characterization of titanium dioxide core and polymer shell hybrid composite particles prepared by two-step dispersion polymerization

Titanium dioxide core and polymer shell composite poly (styrene-co-divinylbenzene)-methacrylic acid [P (St-co-DVB)-MAA]] particles were prepared by two-step dispersion polymerization. Fourier transform IR spectroscopy and elemental analysis were used to measure the content of methacrylic acid in composites particles. X-ray measurement photoelectron spectroscopy (XPS) measurements indicated the presence of an MAA unit on the surface of the composite particles. The combined results of the elemental analysis and the XPS measurements showed that the copolymer on the surface of poly (St-co-DVB)-MAA composite particles was rich in MAA compared with that in the interior of the composite particles. Field-emission scanning electron microscopy (FE-SEM) was used to study the morphology characterization. The composite particles produced showing good spectral reflectance compare with bare TiO₂. TGA results indicated that the encapsulation efficiency and estimated density of composite particles. Encapsulation of TiO₂ was up to 87.4% and the density was ranged from 1.78 to 2.06 g/cm³. Estimated density of the composite particles is suitable to 1.73 g/cm³, due to density matching with suspending fluid.     

项目管理应用于高分子材料与工程综合实验的探索

分析了现阶段高分子材料与工程专业实施综合实验的必要性,从培养适应社会需要的创新意识和工程实践能力人才的角度,提出项目管理教学模式,对专业实验的教学体系、教学内容和教学方法;提出了改革的框架及改革中的一些问题。     

Adsorption of bovine serum albumin to a polymer brush prepared by atom-transfer radical polymerization in a porous inorganic membrane

Protein adsorption was performed by a polymer brush prepared by atom-transfer radical polymerization (ATRP) to a porous inorganic membrane. The porous inorganic membrane, Shirasu Porous Glass made from silica, was modified with a halogen-containing compound to bind the active species for the polymerization. Glycidyl methacrylate was polymerized from the halogen compound by ATRP for a prescribed time, and subsequently chemically modified. The progression of the chemical modification allowed the membrane to lower the phosphate-buffer flux of the porous membrane due to the attachment of the polymer brush. Bovine serum albumin (BSA), as a model protein, was adsorbed at 12 mg per gram of the membrane in permeating BSA solution through the polymer-brush-attached porous membrane.     

Evolution of microstructure and properties of Si3N4 whisker reinforced composites during densification by polymer infiltration and pyrolysis

Si₃N₄ whisker (Si₃N_4w) reinforced composites were prepared by a near-net shaping process, i.e., gel-casting of the Si₃N_4w preform followed by polymer infiltration and pyrolysis (PIP) densification using polysilazane as precursor. The densification process by PIP was described mathematically, after which several key parameters affecting densification efficiency were discussed. The small pore size (0.04 ～ 1 μm) of Si₃N_4w preform can cause filtration effect (low permeability of precursor with a molecular size bigger than pore size), which resulted in the density gradient of the composites. Porosity (P) dependence of flexural strength and elastic modulus of Si₃N_4w/Si₃N₄ followed a power law of (1 – P). With increasing density, the response of Si₃N_4w when confronting cracks transformed from whisker debonding to whisker fracture, which was supposed to be due to the increase of whisker/matrix interface strength. The Si₃N_4w/Si₃N₄ developed by us achieved a good balance between high strength and low dielectric constant, making it promising for high-temperature wave-transparent application.     

Numerical and experimental approach to testing the adhesive properties of modified polymer blend based on EVA/PMMA as coatings for optical fibers

The adhesive properties of polymer blends based on poly(ethylene-co-vinyl acetate) (EVA) and poly(methyl methacrylate) (PMMA) were studied. Two samples were prepared, whereby one kind was a physically mixed blend of commercial polymers in a solution of toluene and the other was a blend with EVA-g-PMMA polymer in a toluene solution, produced via in situ free radical polymerization using redox system initiators. A scanning electron microscopy (SEM) revealed the improved microstructure that was achieved blending with graft polymer that could also be seen by FTIR spectral analysis. Optical fibers were glued together using both of the solutions and subjected to a micro mechanical testing machine. The adhesion test showed that the graft copolymer had enhanced mechanical properties as an adhesive than the physical polymer blend. Optical microscopy of the samples after the adhesion test enabled the determination of the type of adhesive failure. Image analysis of the SEM micrographs was used to determine an area of the contact surface, and characterization microstructure. These results were then implemented in a numerical simulation that demonstrated the influence of microstructure on the adhesive properties showing the stress distribution for both samples. The main aim of obtaining an adhesive with uniform structure, great miscibility of the polymers, and good mechanical and adhesive properties was achieved and a numerical model was established that can be used in selecting the adhesive.     

Pore structure and thermal oxidation curing behavior of porous polymer derived ceramics with superhigh porosity fabricated by freeze casting

Porous ceramics with porosity up to 92.5 % have been successfully fabricated by freeze casting of polycarbosilane (PCS) solution. The effect of PCS concentration and thermal oxidation curing on the pore structure and compressive properties was investigated. Curing mechanism and thermodynamics were illuminated through analyzing the molecular structure, curing activation energy, and curing degree. Porous ceramics, mainly composed of SiC and a small amount of SiO₂, have dendritic pore structure which well replicates the solidification morphology of camphene solvent. Results of FT-IR and Gaussian computation of PCS electron density show that Si–H and Si–CH₃ bonds play a dominant role in thermal oxidation curing reaction. Both curing degree and ceramic yield increase with the increase in curing temperature and time. The curing degree of Si–H bond is close to 52 % and the corresponding ceramic yield is about 83 % when the porous PCS was cured at 200 °C for 90 min. Both polymer concentration and curing time have influences on the compressive strength of porous ceramics.     

Modified van Laar’s Equation and Its Application to VLE ofPolymer Solutions

The original van Laar‘s theory has been modified. The internal pressures of components and mixture are expressed by Prank‘s relation and the excess entropy for mixing of components is also considered. A new activity coefficient equation, which can be satisfactorily applied to polymer solutions, is obtained. The calculated results for the VLE of 179 polymer solutions show that the accuracy of fit is evidently superior to UNIQUAC equation.     

The degradation behavior of C/SiC composites fabricated by polymer impregnation and pyrolysis process under simulated space atomic oxygen environment

Carbon fiber reinforced silicon carbide (C/SiC) composites fabricated by polymer impregnation and pyrolysis (PIP) have been exposed in simulated space atomic oxygen (AO) environment for up to 15 h. The mechanical properties and chemical composition of PIP C/SiC composites have been studied. The results show that the mass loss of the composites increases at the beginning and then decreases as the exposure time lasts. The flexural properties of C/SiC composites have no obvious changes after up to 15 h exposure in AO. C/SiC composites have been oxidized slightly by AO. The amorphous carbon in the matrix has been oxidized to CO or CO₂ gas and SiC has been oxidized to SiO gas and SiO₂.     

Preparation of PBAS core-shell structured polymer by seeded emulsion polymerization and investigation in AS resin toughness

The preparation of poly(n-butyl acrylate)/poly(acrylonitrile-co-styrene), i.e., poly(BA)/poly(AN-co-St) (PBAS) core-shell structured modifier with controlled particle size was reported, and the mechanical properties of AS/PBAS blends were investigated. The modifier was prepared at a solid content of 50 wt % by a two-stage sequential emulsion polymerization. Dynamic light scattering (DLS) was used to monitor the particle diameters and showed that the particles grew without significant secondary nucleation occurring. The morphology was confirmed by means of transmission electron microscopy (TEM). According to the research on mechanical properties of the AS/PBAS blends, a remarkable toughening effect of PBAS on AS resin was found. By means of scanning electron microscopy (SEM) observation, the toughening mechanism was proposed to be crazing caused by rubber particles and shear yielding of AS matrix. Uniform dispersion of rubber particles in AS matrix was attributed to the good compatibility between AS and PBAS modifier. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012