Crosslinking cotton cellulose with aldehydes

The relative effectiveness of several aldehydes in crosslinking cellulose of cotton fabric was determined using a pad-dry-cure treatment and a treatment by immersion in a solution at room temperature. Aldehydes ranked in the same order of ability to crosslink in both treatments. Factors related to crosslinking ability are discussed. The aldehydes crosslinking to the greater extent hydrated readily in water because the aldehyde group was activated or because cyclic hydrates could be formed.     

Crosslinking of styrene-butadiene rubber with polyurethanes bicapped with benzyocyclobutene

Summary A polyurethane prepared from 1,9-nonanediol and toluene-2,4-diisocyanate with M_n=11,840, was capped on both ends in a reaction with 4-(benzocyclobutenyl) methanol. The polyurethane was used to crosslink styrene-butadiene rubber through Diels-Alder reactions on the benzocyclobutene functionality. The synthesis and characterization of 4-(benzocyclobutenyl) methanol, a molecule not reported previously, is presented. The crosslinking reaction was carried out on intimate mixtures of the telechelic polyurethane and SBR at elevated temperature and pressure. Various physical properties of the crosslinked material were studied.Work done at the Department of Chemistry, University of Akron, Akron, OH 44325, USA     

Crosslinking of polybutadiene rubber without any vulcanization agent

Polybutadiene rubber with 10% vinyl unsaturation has been crosslinked without the addition of any vulcanization chemicals. The crosslinks have been created through treatment at high temperature (240–250°C) and elevated pressure (<293 MPa) in a plunger type mold. The treatment time needed to achieve a crosslinked material is of the order of a few minutes and the reaction rate is shown to be dependent upon the temperature as well as upon the pressure applied. As a result of the severe treatment, some degradation reactions may be expected but careful FTIR analysis shows no increased oxidation. There is some consumption of the vinyl unsaturation, to an amount comparable to the number of crosslinks formed. The presence of carbon black increases the measured crosslink density, as expected, but at higher pressures the amount of extra network material, because of the carbon black, is much larger than at lower pressures, suggesting that the carbon black plays a critical role in the network formation process. The stress relaxation properties in compression of the rubber material were investigated and found to be comparable to those of a peroxide vulcanizate.     

液体三元乙丙橡胶的交联及其拉伸性能

研究了由过氧化二异丙苯(DCP)和助交联剂三烯丙基异氰脲酸酯(TAIC)组成的过氧化物体系对液体三元乙丙橡胶(EPDM)的交联及产物拉伸性能的影响.结果表明,液体EPDM的凝胶含量随DCP的增加无明显变化,随TAIC的增加而增加;交联产物的拉伸性能有相似的变化趋势.     

Crosslinking reaction of polyacrylamide with chromium(III)

Summary The crosslinking of initially non-hydrolyzed polyacrylamide with chromium in its +3 valence state was investigated in this work. IR spectra showed that the gelation occurred when the polyacrylamide was hydrolyzed, which implies that the gelation should take place at elevated temperature under neutral condition. The gelation process was monitored by means of viscosity measurement. The addition of acetic acid to the system might lead to the delay of gelation, owing to the synergistic effect of chelating with Cr(III) and acidity.     

Maxam推出用于苛刻工况的新优质实心防滑轮胎

采用了四甲基四乙烯基环四硅氧烷和四甲基四氢环四硅氧烷在铂金催化剂的作用下发生硅氢加成反应得到了高交联密度的硬质硅橡胶,制备过程中采用了“液面悬浮”和“阶梯升温”的工艺。利用差示扫描量热仪、傅里叶红外光谱仪、原子力显微镜、邵氏硬度计和热重分析仪分别对其固化过程、表面性能、硬度和热稳定性进行研究,并利用了平衡溶胀法计算了其交联密度。实验结果表明：阶梯升温能有效控制交联反应;硅橡胶具有极低的粗糙度,均方根粗糙度Rq为1.74 nm,平均粗糙度Ra为1.39 nm;邵氏D硬度为78.3;交联密度为2.87′10-3 mol/cm-3;硅橡胶在质量损失为5%时,对应温度为602.1 o C,最终的残余量为83.57%。     

Crosslinking reaction of poly(vinyl alcohol) with glyoxal

Crosslinking reactions are one of the most commonly used techniques to improve physical properties of polyvinyl alcohol (PVA). Commonly used crosslinkers for these reactions are di-functional compounds, such as glutaraldehyde and glyoxal. The hydroxyl groups of PVA react with aldehydes via formation of acetal bonds hence corsslinking could take place. Quantitative analysis of glyoxal crosslined PVA will be described in this report. A convenient FTIR method has been established to analyze degree of crosslinking in PVA. Analysis by ¹H NMR spectroscopy methods will also be described.     

Crosslinking of unfilled carboxylated nitrile rubber with different systems: Influence on properties

The presence of two functional groups, nitrile and carboxyl, in carboxylated nitrile rubber allows it to be crosslinked with different agents. In this study, we examined the influence of different crosslinking agents on the properties of unfilled carboxylated nitrile rubber. Significant differences were found when different crosslinking agents were used, as shown in the vulcanization curves, especially in the variation of the viscous component with the reaction time. The reaction rate was highest when organic peroxide was used, and it was lowest when metallic peroxide or copper sulfate was used. When the crosslinking agents led to the formation of ionic bonds (metallic oxide and metallic peroxide), the carboxylic groups ? COOH had a greater participation in the crosslinking. However, when copper sulfate was used, coordination bonds were formed, and the main contribution was due to the nitrile groups. Tensile strength, tear strength, and abrasion properties were superior when the crosslinking systems used led to the formation of ionic bonds. On the contrary, the compression set was optimum when covalent bonds were formed. Copper sulfate behaved as an intermediate between the two previous situations. The mechanodynamic response of the compounds also depended on the crosslinking agent used. The correlation between crosslink density by swelling in dichloromethane, maximum damping temperature by dynamic measurements, and glass‐transition temperature by differential scanning calorimetry had to be explained in terms of the crosslink type. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

生物酶法催化天然乳胶中过敏蛋白质交联的研究

利用谷氨酰胺转氨酶催化天然乳胶(NRL)水溶性蛋白质(WSP)发生交联,减少天然乳胶中水溶性蛋白质的含量.利用粒径分析、结构表征、十二烷基硫酸钠凝胶电泳实验证明了交联反应的发生.采用这一新技术可以降低天然乳胶制品的过敏性,拓展了其在医疗卫生领域、食品加工等领域的应用空间.     

Crosslinking of cis-1,4-polyisoprene rubber by electron beam irradiation

Various unsaturated polyfunctional monomers were kneaded into cis-1,4-polyisoprene containing fillers under 80°C and then irradiated using an electron beam accelerator to prepare vulcanized rubber with good quality. Results showed that 2G (diethyleneglycol dimethacrylate) is the best sensitizer. The optimal tensile strength of vulcanized IR was obtained by using 14 phr 2G and irradiated to 180 kGy. Compared with the sulfur vulcanizate, greater values of tensile strength, elongation at break, and 100% stress were found with the radiation-cured IR. Their Young's modulus and tan σ were similar. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 113–116, 1997     

Crosslinking of diene polymers via ‘ENE’ reaction with bistriazolinediones

Summary Bistriazolinediones (BTDs) have been used to synthesize a large number of highly crosslinked polydienes by the ene reaction. BTDs have been found to be effective crosslinking agents at room temperature. The crossliked polymers were swollen in benzene, and the crosslink density and the molecular weight between crosslinks were determined by the Flory-Rehner equation.Dedicated to Prof. C.I. Simionescu in honor of his 60th birthday     

Extending NHC-catalysis: coupling aldehydes with unconventional reaction partners

Transition metal catalysis is a powerful means of effecting organic reactions, but it has some inherent drawbacks, such as the cost of the catalyst and the toxicity of the metals. Organocatalysis represents an attractive alternative and, in some cases, offers transformations unparalleled in metal catalysis. Unique transformations are a particular hallmark of N-heterocyclic carbene (NHC) organocatalysis, a versatile method for which a number of modes of action are known. The NHC-catalyzed umpolung (that is, the inversion of polarity) of electrophilic aldehydes, through formation of the nucleophilic Breslow intermediate, is probably the most important mode of action. In this Account, we discuss the reaction of Breslow intermediates with unconventional reaction partners. In two traditional umpolung reactions, the benzoin condensation and the Stetter reaction, some selectivity issues represent significant challenges, especially in intermolecular variants of these reactions. In intermolecular cross-benzoin reactions, high levels of selectivity were recently obtained, even in the hydroxymethylation of aldehydes with formaldehyde. The key to success was careful choice of the NHC catalyst and reaction conditions. Among asymmetric Stetter reactions, intermolecular versions have posed a long-standing challenge. Recently, the groups of Enders and Rovis reported the first selective and efficient systems. We have contributed to this field by developing an efficient intermolecular Stetter reaction for the formation of α-amino acid derivatives, with broad aldehyde scope and high enantiomeric excess. Moreover, tailor-made thiazolylidene catalysts allowed the unprecedented use of nonactivated olefins and alkynes as aldehyde coupling partners. The basis for this reactivity is a unique mode of NHC organocatalysis: dual activation. In a concerted but asynchronous transition state, the positively polarized proton of the Breslow intermediate activates the coupling partner (for example, an olefin), while the nucleophilic enamine moiety starts to attack the activated coupling partner. As a consequence of the concerted nature of this mechanism, excellent values for enantiomeric excess were obtained for many substrates in the intramolecular hydroacylation of alkenes. In addition, thiazolylidene catalysts have enabled the coupling of aldehydes with reactive species, for example, with arynes and with activated alkyl bromides. NHC catalysis should continue to flourish and lead to surprising developments. One remaining challenge is the asymmetric intermolecular hydroacylation of unactivated olefins. In this area, metal-based catalysts have shown promising early results, but they are far from being either general or practical. It will be interesting to see which class of catalyst, whether metal-based or NHC-based, eventually develops into the method of choice.     

Crosslinking of carboxylated nitrile rubber (XNBR) induced by coordination with anhydrous copper sulfate

BACKGROUND: Crosslinking induced by non‐covalent interactions in rubber materials is currently attracting a great deal of interest because of its perceived reversibility. Some thermoplastic elastomers and ionic elastomers, which are crosslinked by physical entanglements and ionic bonds, respectively, have already been investigated. The present work is centred on the study of the influence of coordination bonds on the physical properties of crosslinked materials. These bonds are formed on addition of copper sulfate. RESULTS: In this context, the effect of crosslinking of carboxylated nitrile rubber (XNBR) by anhydrous copper sulfate (CuSO₄) on crosslink reaction and mechanical and mechano‐dynamic properties is studied. The influence of different levels of CuSO₄ and the addition of conventional filler, carbon black, on the network is studied. The presence of nitrile (? CN) in the elastomeric chains leads to the formation of coordination bonds with the nitrile groups. The formation of ionic bonds between copper ions and carboxylic groups can be deduced from X‐ray photoelectron, attenuated total reflectance Fourier transform infrared and NMR analyses and vulcanization measurements. The dynamic response of the material does not show a secondary transition, the so‐called ionic transition typical of ionic elastomers, since ionic bonds do not lead to a separated ionic microphase, immersed in the elastomeric matrix. CONCLUSION: As expected, the crosslink density of the polymer network increases with the amount of crosslinking agent. Because of the presence of polymer–filler interactions, an increase in crosslink density is observed. However, these interactions seem not to affect the formation of coordination or ionic bonds. Copyright © 2008 Society of Chemical Industry     

Crosslinking reaction of polyacrylate soap‐free hydrosol with zirconium chelate

The crosslinking reaction mechanism of polyacrylate copolymer (monomer mass ratio of methyl methacrylate/butyl acrylate/acrylic acid = 48.77:46.69:4.54) hydrosol with triethanolamine chelate of zirconium isopropyloxide was studied with IR spectroscopy, NMR spectroscopy, differential scanning calorimetry, and ultraviolet spectroscopy. The instrumental analyses on the copolymer mixture heated at different temperatures were investigated, and we proved that the crosslinking adduct had amino groups that were provided by the chelate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3605–3609, 2004     

3－乙酸基酚酮与芳醛缩合反应的研究

本文探讨了３－乙酰基酚酮与ＴＭＢ等芳香醛的羟醛缩合反应。３－乙酰基酚酮与ＴＭＢ、、丁香醛、胡椒醛等取代醛反应分别生成３－（３，４，５－三甲氧基）肉桂酰基酚酮、３－（４－羟基－３，５－二甲氧基）肉桂酰基酚酮、３－（３，４－亚甲二氧基）肉桂酰基酚酮。与桂皮醛反应生成３－（５－苯基－２，４－戊二烯酰基）酚酮等４种尚未见文献报道的新化合物。其结构经红外光谱、核磁共振谱及元素分析得以证实。     

不同微观结构聚丁二烯橡胶的自由基接枝反应

以过氧化苯甲酰(BPO)为引发剂,2,2,6,6-四甲基哌啶-1-氧基自由基(TEMPO)为自由基捕捉剂,进行3种低相对分子质量模型聚丁二烯,即高乙烯基聚丁二烯橡胶(HVPB)、高反式聚丁二烯橡胶(HTPB)及高顺式聚丁二烯橡胶(HCPB)的自由基接枝反应,并利用傅里叶变换红外光谱和核磁共振氢谱对模型聚丁二烯接枝产物的...     

4-氨基脲嘧啶与溴化丁基橡胶反应制备热可逆交联丁基橡胶

在相转移催化剂作用下,用4-氨基脲嘧啶与溴化丁基橡胶(BBR)反应制备了热可逆交联丁基橡胶(IIR),考察了取代反应的影响因素,并研究了含有4-氨基脲嘧啶基团的IIR的结构与拉伸性能.结果表明,4-氨基脲嘧啶取代了BBR中的溴原子,且伯溴代烯丙基结构中的溴原子被完全取代,仲溴代烯丙基结构中的溴原子大部分被取代;IIR上的4-氨基脲嘧啶基团可通过氢键自组装形成热可逆网络结构;在4-氨基脲嘧啶用量为0.010 mol、相转移催化剂四丁基溴化胺/4-氨基脲嘧啶(摩尔比)为1:1、氢氧化钾水溶液/甲苯溶液(体积比)为50:80、反应温度为80 ℃、反应时间为4 h的条件下,4-氨基脲嘧啶与BBR反应后溴原子取代率最大值可达到77%;含有4-氨基脲嘧啶基团的IIR的拉伸强度较BBR增大了2倍,具有热塑性弹性体特征.     

Sorption and diffusion of aldehydes and ketones into natural rubber blends

Sorption and diffusion of aldehydes and ketones through different NR blends of bromobutyl (BIIR), chlorobutyl (CIIR), neoprene, EPDM, polybutadine, and SBR were studied at 25, 40, and 60°C. From the data, the Arrhenius activation parameter for diffusion, E_D, was determined. From the temperature dependence of the sorption constant, the enthalpy of sorption, ΔH, and entropy of sorption, ΔS, were also determined. The activation parameters are found to follow the conventional trend. Transport properties are affected by the nature of the interaction of solvent molecule, by its size, and also by the structural variation of the elastomers. For all the solvents, the polymer blends remained intact but the blends in the presence of benzaldehyde showed degradative reactions at higher temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 101–112, 1998     

Fire reaction properties of concrete made with recycled rubber aggregate

This study investigates the fire reaction properties of concrete made with recycled rubber aggregate (CRRA). Four different concrete compositions were prepared: a reference concrete (RC) made with natural coarse aggregate and three concrete mixes with replacement rates of 5, 10 and 15% of natural fine and coarse aggregate by recycled rubber aggregate (RRA) obtained from used tyres. Specimens of CRRA were tested in a cone calorimeter according to the test standard ASTM E1354, submitted to heat fluxes of 25, 50 and 75kW/m². These tests evaluated the effects of incorporating RRA in the fire reaction properties of concrete, namely in the heat release rate, the time to ignition (TTI), the remaining mass, the production of smoke, and the release of carbon dioxide and carbon monoxide. Owing to the organic nature of RRA, with the exception of the carbon monoxide yield, higher replacement rates of natural aggregates by RRA and increasing heat flux led to a worse fire reaction response, particularly in terms of TTI, heat release rate and smoke production. Results of these experiments were then used to estimate the European fire reaction classes of each concrete composition, using a flame spread model. All CRRA compositions tested were provisionally rated as class A2 or B and such ratings allowed defining the field of application of each solution under analysis, according to building code requirements. Copyright © 2011 John Wiley & Sons, Ltd.     

Crosslinking junctions of vulcanized natural rubber analyzed by solid-state NMR spectroscopy equipped with field-gradient-magic angle spinning probe

Crosslinking junctions of vulcanized natural rubber were analyzed by solid-state NMR spectroscopy equipped with a field-gradient high speed magic angle spinning probe. Resolution of ¹H and ¹³C NMR spectra and correlations between ¹H and ¹³C of the vulcanized natural rubber were investigated by one- and two-dimensional measurements, including inverse correlation measurements. The number of substitution of the carbon atom at the crosslinking junctions was determined by solid-state NMR spectroscopy.