Thermal Evolution of Hybrid Organic-Inorganic Gels Derived from Reaction of 1,4 Butanediol with Tetraethoxysilane

Transparent monolithic discs of organic-inorganic hybrid gels have been prepared by hydrolysis-condensation reactions of tetraethyl orthosilicate with 1,4 butanediol. The gels and glasses have been characterized by infrared spectroscopy and ²⁹Si MAS NMR. The characterization of the gels by infrared spectroscopy showed the incorporation of carbonaceous groups in the polymeric structure and Si–C bonding in the glasses. Pyrolysis of the gels has been studied using thermal analysis. It showed that the pyrolysis of the gels occurs in two temperature domains. The first is below 400°C due to condensation reactions and second is in the temperature range 450–550°C due to decomposition of carbonaceous groups and crosslinking. Pyrolysis of the gels at 1000°C resulted in X-ray amorphous, hard black glasses similar to oxycarbide glasses obtained by pyrolysis of siloxanes. On further heat treatment to 1400–1600°C, development of cristobalite structure and crystalline silicon carbide is observed in the otherwise amorphous black mass. The pyrolysed materials have been found to exhibit good resistance towards oxidation at 1000°C.     

Improved UHMWPE through the control of sterilization dose and atmosphere

In this study, the effects of sterilization dose and atmosphere on UHMWPE wear properties and crosslinking were examined. The relationship between crosslinking and adhesive / abrasive wear mechanisms of acetabular cups was investigated.

The use of a vacuum sterilization atmosphere resulted in improvements in the wear resistance of UHMWPE for the adhesive/abrasive wear mechanisms for the doses examined in this study. The two measures of crosslinking, swelling ratio and gel fraction, values can be used to predict hip simulator wear rates over the sterilization dose range of 0 to 50 kGy for the vacuum atmosphere samples. Of the two measures, the swelling ratio is a more sensitive measure of the extent of crosslinking, particularly for highly crosslinked materials and therefore a more sensitive predictor of adhesive/abrasive wear rates.     

ESCA applied to polymers. XVIII. RF glow discharge modification of polymers in helium,neon, argon,and krypton

The crosslinking of an ethylene–tetrafluoroethylene copolymer by exposure to a variety of inert gas plasmas, excited by an inductively coupled radiofrequency (RF) field, has been studied. The rates for direct and radiative energy-transfer processes are determined within the framework of a kinetic model of the system and are shown to have a strong dependence on the sustaining gas, as do the average depths of penetration of the ions and metastable species. Helium is found to be the most efficient gas for the crosslinking of the outermost few monolayers whereas the crosslinking of the subsurface and bulk polymer is best effected by neon. Madelung charge potential calculations have been performed to simulate the experimentally determined x-ray photoelectron spectroscopy (ESCA) spectra to elucidate several features of the mechanisms involved.     

Rheology and rheokinetics of triethanolamine modified carboxymethyl hydroxyethyl cellulose

To meet requirements of fracturing fluid thickener, triethanolamine was used to modify carboxymethyl hydroxyethyl cellulose (CMHEC) to obtain product called T-CMHEC of high viscosity. Rheological properties of CMHEC and T-CMHEC solutions were investigated to compare its structure and rheological performance, including viscosity, flow curve, thixotropy, and viscoelasticity. Viscosities of CMHEC and T-CMHEC solutions are, respectively, 19.0 and 63.2?mPa?·?s for the same concentration of 0.3%. Viscosity of T-CMHEC solutions is 3.3 times of CMHEC ones. Besides, the thixotropy and viscoelasticity of T-CMHEC system are both getting stronger than before. In summary, the T-CMHEC system shows better rheological performance after modification. Crosslinking process of T-CMHEC system is investigated under steady shear under different conditions, containing shear rates, concentrations of crosslinking agent, concentrations of pH adjuster, and temperature. Viscosity curves changing with time are obtained during crosslinking process. Four-parameter crosslinking rheokinetics equation is suitable to fit the viscosity curves under different conditions. Study on crosslinking process of T-CMHEC solutions is helpful to deepen the understanding on gel formation, and provides a theoretical basis for its application.     

The role of molecular diffusion in the adhesion of EPDM and EPR elastomers

Adhesion of lightly crosslinked sheets of EPDM (ethylene–propylene–diene terpolymer) to themselves and to a Mylar substrate has been investigated over wide ranges of peel rate and test temperature. The effect of incorporating ethylene–propylene copolymer (EPR) before crosslinking, to yield a loose macromolecular network containing dissolved linear EPR macromolecules, was also studied. The self-adhesion of these materials was found to be much greater than their adhesion to Mylar, over a wide range of effective peel rates. This is attributed to interdiffusion of EPR and EPDM molecular strands. At extremely low peel rates the enhancement of adhesion was smaller, probably because of back-diffusion, and at high rates, the strength of adhesion became high in all cases. These results are compared to those obtained previously for polyisobutylene-co- isoprene networks containing linear polyisobutylene molecules. The enhancement of self-adhesion at intermediate rates of peel was considerably greater for the EPDM-based materials, probably because of a lower degree of crosslinking and a greater tendency to form molecular entanglements.     

Free-radical reactions under diffusional constraints: orientation does matter in hydrogen transfer

Pyrolysis of silica-immobilized 1,3-diphenylpropane at 375 degrees C has been examined in the presence of a series of isomeric (by point of attachment) co-attached hydroaromatic spacer molecules. Under the diffusional constraints, the pyrolysis rate is sensitive to the orientation of the spacer molecule, which must transfer hydrogen to intermediate benzylic radicals on the surface. Spacer molecules possessing a meta-orientation of the benzylic hydrogens with respect to the surface linkage are able to attain a better geometry for the hydrogen transfer on the surface resulting in faster reaction rates.     

Effect of stabilizer and pigment on photodegradation of polypropylene as revealed by macromolecule scission and crosslinking measurements

Photodegradation depth-profiles have been generated using computer-aided molecular weight distribution analysis for 3 mm thick polypropylene injection moldings containing (i) a stabilizing package that included hindered amine light stabilizers and a phenolic stabilizer, (ii) titanium dioxide pigment and (iii) both the pigment and the stabilizing package. The inhibiting effect of the additives has been determined quantitatively by comparing macromolecule scission and crosslinking rates with those in samples containing no stabilizer or pigment. TiO₂ pigment gave more effective protection against molecular degradation than the stabilizer package; there was very little advantage to be gained by adding stabilizer when the pigment was present. The inhibition caused by having pigment or stabilizer present was measured to be very large: degradation was reduced by at least a factor of 10 and often by a factor of several hundred times. The relative amount of scission and crosslinking differed according to the additives present and the depth from the exposed surface: high reaction rates favoured scission and lower reaction rates resulted in a higher relative crosslinking concentration.     

原煤和黑液水煤浆燃烧特性的热分析对比研究

在热天平上进行黑液水煤浆和原煤的燃烧、热解实验,得到不同升温速率下的燃烧、热解特性曲线和碳转化率特征曲线。试验结果表明,黑液水煤浆中的钠及其化合物在燃烧过程中催化作用明显,并且黑液中有机物成分对燃烧起到一定促进作用。在20 ℃/min升温速率下黑液水煤浆和原煤的燃烧活化能分别为12.98 kJ/mol和106.59 kJ/mol,反映出黑液水煤浆比原煤有更好的着火特性。     

o-Carborane-Containing Poly(siloxane-arylacetylene)s With Thermal and Thermo-Oxidative Stabilities

A series of poly(siloxane-arylacetylene)s with o-carborane in the backbone (CB-PSOA)s were prepared by the coupling reaction between poly(siloxane-arylacetylene) (PSOA) and decaborane (B₁₀H₁₄) in the presence of CH₃CN. CB-PSOAs were characterized by Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). The results show that the average amount of carborane units in a CB-PSOA chain could be raised when the molar ratio of B₁₀H₁₄ to PSOA is increased from 0.6 to 2.4. The crosslinking reaction could be carried on at above 140°C for CB-PSOAs. The CB-PSOA thermosets show excellent thermo oxidative stability with over 85% residue yield at 1000°C in air.     

毛竹酶解/温和酸水解木质素的快速热解研究

采用热裂解-气相色谱/质谱仪联用技术,研究毛竹酶解/温和酸水解木质素(简称EMAL)的热解特性和热解产物的分布与形成规律.以温度为重要因素,研究其对木质素快速热裂解产物的影响,并通过主要的热解产物推断热解反应途径.研究结果表明,EMAL的热解产物主要是2,3-二氢苯并呋喃、酚类、脂类和少量乙酸.热解温度对热解产物组分的相对含量有显著影响,250~400 ℃时,产物主要是2,3-二氢苯并呋喃,320 ℃时其相对含量最高,达到66.26%;400~800 ℃时,热解产物主要是酚类,600 ℃时其相对含量最高,达到62.58%;800 ℃时出现了少量的乙酸.     

Isobutylene‐rich macromonomers: Dynamics and yields of peroxide‐initiated crosslinking

New isobutylene‐rich elastomers bearing multiple pendant styrenic, acrylic, maleimidic, vinylic, and allylic functional groups have been prepared and examined in the context of peroxide‐initiated crosslinking. Halide displacement from brominated poly(isobutylene‐co‐isoprene) (BIIR) by the requisite carboxylate nucleophiles in homogeneous toluene solutions provide the desired esters in quantitative yield without complications from dehydrohalogenation or premature crosslinking. Heating the resulting macromonomers with dicumyl peroxide to 160 °C under solvent‐free conditions gives thermoset derivatives, with reaction rates and yields depending markedly on functional group structure. In general, high cure extents can only be achieved using highly reactive pendant functional groups, owing to the competitive balance between crosslinking through C?C oligomerization, and degradation through β‐scission of backbone macroradical intermediates. Independent control of crosslinking rates and cure extents is gained through the use of nitroxyl radical traps bearing acrylate functionality. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 123–132     

流变学法研究部分水解聚丙烯酰胺/Cr(III)交联反应I.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺（HPAM）/Cr(III)交联体系的 反应动力学。HPAM溶液的粘性模量G”大于弹性模量G’,且其数值随时间不发生变 化,体系为粘性溶液。而HPAM/Cr(III)体系的G’和G”的数值都随时间变化,G” 在反应开始阶段大于G’,当反应进行一段时间后,G’超过G”占据主要地位,体 系成为弹性体系。交联过程可分为三个阶段：第一上升阶段,平缓上升阶段和第二 上升阶段。利用G’～ t曲线可以推测反应机理。实验发现成胶速率随反应物HPAM 和Cr(III)的浓度的增加而增加,而成胶时间缩短。在羧基浓度过量的情况下,交 联反应对Cr(III)浓度的反应级数是1。凝胶的有效弹性交联密度随聚合物浓度的增 加而增,且随凝胶反应的进行而增加。凝胶的交联点间的平均分子量随Cr(III)浓 度的增加和交联反应的进行而下降。     

Felddesorptions-Massenspektrometrie biologisch wichtiger Substanzen

Following the introduction into the experimental methods and theory of field desorption three important applications of FD-MS to biologically significant compounds are discussed: 1. Structure determination or identification of certain classes of organic compounds. 2. Pyrolysis FI- and FD-MS of bacteria. 3. Pyrolysis FD-MS of DNA.     

Synthesis of perfluorinated cation exchange membranes by preirradiation grafting of acrylic acid onto ethylene-tetrafluoroethylene films

Hydrophilic carboxyl-containing fluoromembranes were obtained by preirradiation grafting of acrylic acid onto ethylene-tetrafluoroethylene film. The dependence of the grafting reaction on temperature, monomer concentration, nature and concentration of inhibitor, crosslinking agent, solvent, and on the preirradiation dose was investigated. The grafting rates increase with temperature, whereas the saturation degree of grafting (SDG) decreases. Addition of inhibitor minimizes homopolymerization and at the same time hinders the grafting reaction. The SDG increases markedly with monomer concentration until it reaches a maximum and thereafter decreases. The grafting rates increase with preirradiation dose. Addition of crosslinking agent initially decreases the SDG, and thereafter increases. The highest grafting rates are obtained using water as solvent followed by methanol and ethanol. The results are discussed on the basis of various parameters: interaction between monomer diffusibility and the viscosity of the monomer bath, the mutual reactivity of monomer, and the crosslinking agent. An agreement is observed between the values of the electrical resistance and the saturation degree of grafting. © 1996 John Wiley & Sons, Inc.     

Molecular weight distribution formed through chain-length-dependent crosslinking reactions

The molecular weight distribution formed through chain-length-dependent crosslinking reactions in free-radical vinyl/divinyl copolymerization is investigated by using Monte Carlo simulations. When the crosslinking reaction rates for larger polymer molecules are reduced, the high molecular weight tails cannot extend smoothly, resulting in distorted, sometimes bimodal distribution profiles, which exhibit qualitative similarity with those reported experimentally. Although the reduced crosslinking reaction rates between larger polymer molecules may not affect the average crosslinking density levels significantly, they can delay the developments of the weight-average molecular weight significantly. Because the wastage of pendant double bonds through cyclization would result in a similar tendency, one cannot distinguish these two types of nonidealities through the measurements of the pendant double bond consumption and the average molecular weight development.     

Rheological Properties and Crosslinking Rheo-Kinetics of CMHEC/CTAB Synergistic Systems

Aiming at synergistic interaction between carboxymethyl hydroxyethyl cellulose (CMHEC) and cetyltrimethyl ammonium bromide (CTAB), mixtures of CMHEC and CTAB solutions were investigated, employing relative viscosity and rheological measurements. The effects of mass ratio of CMHEC and CTAB solutions, temperature, and polysaccharide concentration on relative viscosities of CMHEC/CTAB systems were studied. Rheological method was used to study rheo-kinetics of the isothermal crosslinking process for CMHEC/CTAB synergistic fracturing fluid, and the novel crosslinking rheo-kinetics equation was established. The results showed the strong synergism between CMHEC and CTAB, resulting in a higher relative viscosity, storage modulus G′, and loss modulus G″ than that of separate ones. CMHEC/CTAB systems behave as pseudoplastic fluids with considerable thixotropy and viscoelasticity, and the flow behavior can be well described by Carreau?Williamson model. The crosslinking rheo-kinetics equation can well describe the isothermal crosslinking process at different shear rates. The model parameters are well-defined and reasonable.     

生物质废弃物的热解研究

生物质能是可再生能源,在生长过程中通过光合作用将碳和能量固定下来,利用生物质能CO2排放很少.为实现可持续能源生产和减少温室气体排放的目的,中国已于2006年1月开始实施《中华人民共和国可再生能源法》.     

Maleation of poly(3,4‐epoxy‐1‐butene) for accelerated crosslinking in the presence of a redox catalyst

Accelerated crosslinking of novel poly(3,4‐epoxy‐1‐butene) (3,4‐PEPB) oligomers in the presence of a cobalt‐based redox catalyst was investigated. Previous studies using model compounds, 3,4‐dimethoxy‐1‐butene and 1,4‐dimethoxy‐2‐butene, suggested that maleation of hydroxyl‐terminated 3,4‐PEPB oligomers would result in more rapid crosslinking in thin films. Novel maleated oligomers offered a unique combination of both electron‐rich and electron‐poor olefinic sites, and quantitative maleation significantly increased the crosslinking rate of 3,4‐PEPB. Efficient copolymerization between terminal maleate groups and olefinic groups in the repeating unit was proposed to account for accelerated crosslinking rates. Furthermore, the addition of novel reactive diluents, such as maleic acid mono‐ethyl ester, also effectively improved the 3,4‐PEPB crosslinking rate. Sol fraction measurements as a function of coating thickness revealed that the crosslinking rate versus oxygen diffusion was less significant for the maleated oligomers because of the presence of reactive electron‐poor olefins. Sol fractions were constant for catalyst concentrations greater than 0.25–0.50 wt % (as compared with oligomer feed). This observation suggested that a redox process was not a dominant factor in determining crosslinking rates at various experimental conditions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2789–2798, 2002     

Intermolecular condensation products formed during the pyrolysis of peptides

Mass Spectrometry (MS) analysis of pyrolysis products of simple peptides has revealed several non-volatile thermal degradation products at masses lower than the precursor peptide. In addition to these products, many other signals were also observed at higher masses than the precursor peptide, and their characterization is the focus of this study. Here we report on the observation of homo and hetero condensation peptide products formed during the pyrolysis of peptides. The observed peptide condensation products are formed between two, three or even four peptides. Tandem MS (MS/MS) analyses of these products showed that C-terminal to N-terminal intermolecular bonding is preferred during pyrolysis when combining two peptides, rather than involving crosslinking between basic and acidic side chain groups like arginine and aspartic acid. These observations are rationalized by steric hindrance effect and known pK_a values of the peptide C- and N-termini and amino acid side groups like aspartic acid and arginine. Pyrolysis of a standard N-acetylated peptide showed no detectable condensation and/or crosslinked products, even in peptides with basic side groups, providing further evidence for the C-terminus to N-terminus intermolecular bonding between peptides under pyrolytic conditions.     

Novel Approach to Fabricate Carbon Molecular‐Sieve Membranes Based on Consideration of Interpenetrating Networks

Summary: Carbon molecular‐sieve membranes (CMSMs) have shown great potential for gas separation. They exhibit high selectivity by permitting effective size‐ and shape‐separation between gas molecules of similar molecular dimensions. Hence, the control of their pore size is very important. While previous studies have focused on the conditions of pyrolysis and its effect on CMSM properties, a novel approach is reported here whereby the precursor polymer is chemically modified prior to pyrolysis and the resultant CMSM was investigated for its gas separation properties. Pyrolysis of chemically crosslinked and uncrosslinked Matrimid® resulted in a change in d‐spacing from 5.6 to 3.6 and 3.7 Å, respectively. The crosslinked CMSM also exhibited greater ordering in its packing. The Matrimid‐derived CMSMs exhibited excellent separation properties for CO₂/CH₄.

Mechanism of chemical crosslinking modification.