氮官能化多锂引发丁二烯/异戊二烯/苯乙烯聚合动力学

以自制氮官能化多锂(以下简称Li)为引发剂,N,N,N′,N′-四甲基乙二胺(TMEDA)为极性调节剂,环己烷为溶剂,对苯乙烯(St)、异戊二烯(Ip)、丁二烯(Bd)进行负离子聚合,合成了星形集成橡胶丁二烯-异戊二烯-苯乙烯三元共聚物(SIBR),研究了不同TMEDA/Li(摩尔比)下SIBR的聚合反应动力学。结果表明,在三元共聚合反应中,3种单体的反应速率与其各自浓度均符合一级动力学关系;在SIBR的合成体系中,随着TMEDA/Li的增大,Bd的反应速率常数先升高后降低,St的反应速率常数逐渐增加,Ip的反应速率常数逐渐降低;当TMEDA/Li为1·0、二乙烯基苯(DVB)/Li(摩尔比)为0·8、引发剂浓度为7·69×10-4mol/L时,单体Bd,Ip,St的表观增长反应活化能分别为31·59,47·64,31·76kJ/mol,链增长频率因子分别为1·02×104,1·09×106,5·27×103min-1。     

二乙二醇单乙醚基钡/三异丁基铝/正丁基锂体系引发合成反式-1,4-聚异戊二烯

以正丁基锂(简称Li)为主引发剂、二乙二醇单乙醚基钡(简称Ba)和三异丁基铝(简称Al)为助引发剂、环己烷为溶剂,对异戊二烯(Ip)聚合反应动力学及产物的微观结构进行了研究。结果表明,在Ba/Al/Li引发的聚合体系中,Ip的聚合反应速率与单体浓度呈动力学一级反应关系,假一级表观增长反应速率常数和表观增长反应活化能均与引发体系的三组分摩尔比相关;Al是引发体系中重要的活性组分,且随Ba/Al/Li引发体系中Al用量的增加,聚合反应速率先升高后下降,当Ba/Al/Li(摩尔比)为1/4/4时,聚合反应速率达到最大;Ba在调节聚异戊二烯反式-1,4-结构摩尔含量中的作用大于Al;聚合温度对聚合产物微观结构含量基本无影响。     

磷酸酯钕系催化剂合成高顺式丁二烯-异戊二烯共聚物

以2-乙基己基磷酸单2-乙基己基酯钕盐(简称Nd)/氢化二异丁基铝(简称Al)/一氯二乙基铝(简称Cl)为催化剂进行丁二烯(Bd)和异戊二烯(Ip)共聚合,考察了反应条件对聚合反应的影响,并对产物结构进行了表征。结果表明,Nd/Al/Cl催化体系具有单一活性中心,所合成的Bd-Ip共聚物为无规共聚物。催化剂制备时Ip用量越大,聚合活性越大,共聚物的分子量分布越窄。在c(Ip)/c(Nd)为50、c(Al)/c(Nd)为10、c(Cl)/c(Nd)为1.0,于60℃陈化2 h制备催化剂,然后以己烷作溶剂,在c(Nd)/c(Bd)为6.8×10-4、Bd/Ip(摩尔比)为1/1的条件下,于50℃聚合8 h,所得Bd-Ip共聚物具有高顺式结构,聚丁二烯链段的顺式-1,4-结构摩尔分数为95.2%,聚异戊二烯链段的顺式-1,4-结构摩尔分数为97.4%,且分子量分布较窄,为2.45。     

锡偶联型充油苯乙烯-异戊二烯-丁二烯三元共聚物的合成

以正丁基锂为引发剂、环己烷为溶剂、自制的二元复配调节体系为调节剂、四氯化锡为偶联剂,采用负离子聚合法合成了锡偶联型苯乙烯(St)-异戊二烯(Ip)-丁二烯(Bd)三元共聚物(SIBR),并用湿法充油技术制备了充油SIBR,研究了调节剂对SIBR三元共聚动力学的影响,考察了单体配比和微嵌段含量对SIBR及充油SIBR性能的影响,并对比了充油SIBR与3种通用胶(溶聚丁苯橡胶2305、乳聚丁苯橡胶1502和1712)的性能。结果表明,在SIBR三元聚合过程中,不添加调节剂时,Bd、Ip、St的聚合速率依次减慢,且St的聚合速率远小于前两者;在添加复配调节剂后,St的聚合速率大幅度提高,并超过Ip的聚合速率;当St/Ip/Bd(质量比)为20/40/40时,SIBR的300%定伸应力和拉伸强度呈现最大值;当St微嵌段质量分数小于1.0%时,充油SIBR具有良好的物理机械性能及优异的动态力学性能;充油SIBR的物理机械性能基本与3种通用胶相当,抗湿滑性优于3种通用胶,且滚动阻力小于3种通用胶。     

异辛酸铁/三异丁基铝/亚磷酸二乙酯催化丁二烯-异戊二烯共聚合

以异辛酸铁(简称Fe)/三异丁基铝(简称Al)/亚磷酸二乙酯(DEP)为催化剂催化丁二烯(Bd)与异戊二烯(Ip)共聚,考察了Al用量、DEP用量及单体配比对Bd-Ip共聚合的影响。结果表明,由Fe/Al/DEP组成的催化剂可在己烷中于50℃下催化Bd与Ip共聚,共聚物收率随Al和DEP用量的增加后下降。当Al/Fe(摩尔比)为10、DEP/Fe(摩尔比)为2时,共聚物收率最高为82.9%。当Al/Fe较低时,共聚物仅有1个玻璃化转变温度,为无规共聚物。     

双组分钛基催化剂合成反式-1,4-聚异戊二烯/3,4-聚异戊二烯复合胶

以钛酸正戊酯[Ti(C5H11O)4]-TiCl4/MgCl2(简称Ti)-Al(Et)3(简称Al)组成的双组分钛基催化剂引发异戊二烯(Ip)聚合,原位合成反式-1,4-聚异戊二烯(TPI)/3,4-聚异戊二烯(PIp)复合胶,考察了聚合活性和复合胶在汽油中可溶性的影响因素,表征了复合胶的微观结构,并研究了复合胶的特性黏数。结果表明,在Ti/Ip(摩尔比)为6×10-5、Ti(C5H11O)4/Ip(摩尔比)为1.2×10-3、Al/Ti(C5H11O)4(摩尔比)为10的条件下,聚合活性最优;复合胶的汽油可溶物部分含量变化的趋势遵循以下规律:随着Ti(C5H11O)4用量的增加而增大;随着Al/Ti(C5H11O)4的增大先升高后降低最后趋于平稳;随着Ti/Ip的增大而逐渐降低。TPI的相对分子质量大于3,4-PIp。     

氮官能化多锂引发合成星形苯乙烯-异戊二烯-丁二烯共聚物的微观结构和玻璃化转变温度

以六亚甲基亚胺锂(LHMI)与二乙烯基苯(DVB)合成的氮官能化多锂(简称Li)为引发剂,N,N,N′,N′-四甲基乙二胺(TMEDA)为极性调节剂,环己烷为溶剂,制备了带有氮官能化基团的星形无规苯乙烯-异戊二烯-丁二烯共聚物(SIBR),用核磁共振法进行了表征,并分析了TMEDA用量、聚合温度、引发剂浓度及DVB/Li(摩尔比)对SIBR微观结构和玻璃化转变温度(Tg)的影响。结果表明,在DVB/LHMI(摩尔比)为0.8的条件下,SIBR中有C—N存在,并且为臂数不等的星形聚合物;随着TMEDA用量的增加和聚合温度的降低,SIBR中非1,4-结构含量增加,Tg提高;在实验范围内引发剂浓度和DVB/Li对SIBR中非1,4-结构含量和其Tg影响不大。     

星形苯乙烯-异戊二烯-丁二烯嵌段共聚物结构与性能的关系

以环己烷为溶剂,苯乙烯(St)、丁二烯(Bd)、异戊二烯(Ip)为单体,正丁基锂为引发剂,采用负离子聚合法合成了集成橡胶———星形苯乙烯-异戊二烯-丁二烯嵌段共聚物(SIBR),考察了星形SIBR的相对分子质量、侧基含量、嵌段比(即Ip的均聚物链段与St-Bd的无规共聚物链段的质量比)与其性能的关系。结果表明,在考察范围内,星形SIBR的拉伸强度和撕裂强度随着其相对分子质量的增加而增大。随着1,2-和3,4-结构含量之和的增加,0℃和60℃时的损耗因子均有所增大。固定St/Bd(质量比)为1/3,随着嵌段比的逐渐降低,所得星形SIBR的门尼黏度逐渐增大;嵌段比为20/80时所得星形SIBR具有较好的力学性能与动态力学性能,且与溶聚丁苯橡胶2300、2305以及天然橡胶相比,具有更好的抗湿滑性和滚动阻力的平衡。     

极性添加剂存在下铝-镍催化体系的苯乙烯-异戊二烯-丁二烯共聚物的氢化反应

采用负离子聚合法合成苯乙烯-异戊二烯-丁二烯三元共聚物( SIBR),并对其结构进行了表征;研究了结构调节剂N,N,N＇,N＇-四甲基乙二胺(TMEDA)、二乙二醇二甲醚(2 G)和四氢呋喃(THF)作外加添加剂时,对三异丁基铝(简称Al)/环烷酸镍(简称Ni)体系(A1与Ni的摩尔比为5)催化SIBR氢化反应的影响....     

星形SIBR共聚物结构与性能的关系研究

北京化工研究院燕山分院以环己烷为溶剂,苯乙烯(St)、丁二烯(Bd)以及异戊二烯(Ip)为单体,正丁基锂为引发剂,采用负离子聚合法合成了集成橡胶——星形苯乙烯-异戊二烯-丁二烯嵌段共聚物(SIBR),考察了星形SIBR的相对分子质量、侧基含量、嵌段比(即Ip的均聚物链段与     

Polymorphism of LiGa5O8 and of LiGa5O8-MgGa2O4Solid Solutions

High-temperature X-ray diffraction and differential thermal analyses showed that LiGa₅O₈ exists in two polymorphs related by the first-order transition at 1138°±3°C of the low-temperature simple-cubic form, space group (probably) O⁷, to the high-temperature spinel (fcc) form, space group O _h ⁷. The transition is rapid, and the high-temperature form in pure LiGa₅O₈ could not be quenched to room temperature under the conditions used. However, the high-temperature polymorph can be quenched under equilibrium conditions when 40 mol% or more MgGa₂O₄ is present. The subsolidus equilibrium relations in the system MgGa₂O₄-LiGa₅O₈ are discussed.     

Magnetoresistance of CuxCo1-xFe2O4 Ferrites

Magnetoresistance measurements (Δ/R) were carried out on Cu _x Co_{1- x} Fe₂O₄ samples with x =1, 0.75, 0.50, 0.25 and cobalt ferrite in the range of magnetic intensity (H) from 1.0 to 4.5 kG. Linear plots were obtained between log (Δ/R) and log H for all compositions except that of cobalt ferrite. The values of n at x =0.5 do not agree with the results of some authors. The discrepancy may be attributed to the value of magnetic field intensity at which such measurements were carried out. The similarity of features of n and μ_D with composition leads us to believe that the magnetoresistance may arise from the scattering of conduction electrons by localized electrons involving the s-d exchange interaction.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm² is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers.     

Raman Study of Glasses of Ba2TiSi2O8 and Ba2TiGe2O8

Raman spectra are reported for fresnoite (Ba₂Ti(Si,Ge)₂O₈ glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba₂TiSi₂O₈ and Ba₂TiGe₂O₈. The Ba₂TiGe₂O₈ glass spectra show correspondence with the Ba₂TiGe₂O₈ crystalline Raman spectra; the v _s(Ge–O–Ge) mode occurs at 518 cm⁻¹ in the glass and at 521 cm⁻¹ in the crystalline material. Five-fold coordinated titanium is the majority species present in the Ba₂TiGe₂O₈ glass as revealed by a strong band at 824 cm⁻¹ in the I glass spectrum. The Ba₂TiSi₂O₈ glass spectra are similar to the Ba₂TiSi₂O₈ crystalline spectrum; the strongest band is found at 836 cm⁻¹ in the I glass spectrum. Through comparison with the previous Raman data of other titania silicate glasses, we conclude that the Ba₂TiSi₂O₈ glass has a structure similar to the crystalline phase.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS₂” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO₃ species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.