丁二烯阴离子聚合的理论研究(中)

三、有机锂的紫外吸收光谱 本文中的有机锂仅包括正丁基锂(n-BuLi)及聚丁二烯基锂(PBLi)两种。研究内容为有机锂的缔合度,Lewis碱的络合作用,σ-、π-活性种的紫外吸收光谱理论,以及有机锂与Lewis碱的副反应等。 文献[1]认为,烷基锂的缔合体随烷基基团的性质、溶剂的极性而变化,而n-BuLi在烃类中呈六缔合体,在极性介质中则呈四缔合休。对PBLi而言,Bywater等采用光散射法在烃类中测得的缔合度为4,     

溶聚丁苯和嵌段共聚物的技术开发——非极性溶剂中锂系阴离子聚合的基础理论研究

丁二烯(Bd)与苯乙烯(St)在非极性溶剂如烃类溶剂中用丁基锂引发聚合,主要生成嵌段丁苯共聚物。通过控制两种单体的浓度之比或采用高温聚合,可以制得无规丁苯橡胶。工业生产常采用不同聚合活性种调节单体的表观竞聚率制备无规丁苯橡胶。在非极性溶剂中有极性添加剂存在下的阴离子共聚体系,活性种种类及性质不仅与活性链端的单体单元结构,而且与添加剂用量、聚合温度有关。多活性种的存在对共聚反应、产物组分及微观结构有极大的影响。不同添加剂对聚合体系中活性种种类及活性大小亦有影响,因而导致整个聚     

阴离子聚合(Ⅲ)

3.烃类溶剂中烷基锂为主引发剂的阴离子聚合 第二章讨论的以聚苯乙烯基盐类引发的聚合反应主要是在DOX、THF等极性溶液中进行的,由于反应活性种并不缔合(参看2.2节),所以聚合速度可以直接用(14)式来表示,即聚合增长反应速度对单体浓度     

有机锂的缔合度

本文主要论述文献中有关烷基锂、聚二烯烃基锂、聚丁二烯基氧锂及聚丁二烯基羧酸锂等的缔合度问题。作者根据文献报导数据,同时结合本人近年来的研究结果指出:同一种烷基锂在烃类溶剂中的缔合度,主要随着活性种浓度的不同,可等于2,4,6;而高分子链有机锂的缔合度,则为2,4;在给定浓度下,实测所得有机锂的缔合度,实际上是以某一缔合体为主的混合物的平均值。一般而言,有机锂的缔合度与本身的分了结构、活性种的浓度、单体浓度、测定温度和溶剂性质等因素有关。     

应用高分子分子设计合成节能丁苯橡胶：Ⅱ.链结构形成机理

用阴离子法合成ＳＢＲ，多官能团锂为引发剂，环已烷为熔剂，极性添加剂为无规化剂和结构调节剂。对苯乙烯、１．２－结构单元在分子链上的分布情况进行了研究。对丁苯共聚物的共聚组成，序列分布、微观结构 形成机理进行了探讨。认为在聚合体系中同时存在有丁二烯的π烯丙基活性种、σ烯丙基活性种及苯乙烯活性种。丁二烯与σ烯丙基活性中心反应主要形成１．４－结构，同π烯丙基中心反应主要形成１．２－结构。对于π烯丙基活性中     

Lewis酸改性烷基锂负离子聚合研究进展Ⅰ.烷基锂负离子聚合现状及改性

介绍了烷基锂负离子聚合工艺存在的主要弊端,同时指出适当降低高反应速率的途径是调控活性种的反应性。阐述了Lew is酸改性烷基锂负离子聚合的研究进展,认为酸根型络合物反应性和选择性的设定是调控活性负离子聚合的关键,是研发新型负离子引发体系的重要内容。     

阴离子溶聚丁戊橡胶分子量的研究

以正丁基锂为引发剂，分别以二氧六环（DOX）和二乙二醇二甲醚（2G）为极性调节剂研究了异戊二烯和丁二烯阴离子共聚物分子量随反应时间的变化规律。实验发现，聚合物的分子量与活性种的活性有关，高温严重破坏活性种的活性，调节剂用量是杀死活性种活性的另一因素。聚合前期，分子量随时间的增加而增大；温度升高后，高温破坏了活性种的活性，活性链解缔合导致的粘度下降，所以聚合后期分子量降低。2G对活性链的破坏受温度的影响要小于DOX受温度的影响。     

路易氏碱在阴离子聚合领域中的应用 Ⅱ.活化作用

路易氏碱在阴离子聚合领域中用途十分广泛，其重要性有待进一步认识。本文仅介绍它对活性种（包括引发剂和活性聚合链末端）的活化作用。     

等离子体引发炭黑 接枝聚合的溶剂效应

用等离子体处理炭黑发现,这些等离子体黑颗粒经辉发放电后会产生不同种类的活性种,如高能电子、光子、自由基等,这些活性能引发乙烯基单体进行接枝聚合反应。等离子体炭黑对不同的乙烯基单体具有较强的选择性,当选用不同的溶剂时会产生明显的溶剂效应,产生溶剂效应的原因与等离子体引发聚合的机理有关。等离子体的位阻排斥引发机理会对乙烯基单体的接枝聚合产生较强的选择性。等离子体的溶剂化活性引发机理会对乙烯基单体的接枝聚合产生较强的溶剂效应。当等离子体炭黑与甲基丙烯酸甲脂、甲基丙烯酸丁酯接枝聚合时,溶剂采用二甲基甲酰胺,可得到较高的树枝率。同时讨论了接枝反应的的影响因素。在炭黑颗粒上接枝不同的乙烯基单体会对炭黑体系的分散稳定性产生不同的影响。     

相转移催化

在有机化学反应中,一直存在着如何促进二相之间反应的问题,过去一般多使用能和水发生互溶的极性有机溶剂,如甲醇、乙醇、丙酮、二氧六环等来进行改善。近年盛行如二甲基亚砜(DMSO)、二甲基甲酰胺(DMF)、乙腈(AN)、六甲基磷酰胺(HMPA)等双极性非质子型溶剂(dipolar aprotic solvent),由于它能使阳离子发生强烈的溶剂化作用,因此能很好地溶于有机相中。但是,前者阴离子在极性质子溶剂中受到较强的溶剂化会使反应活性下降;后者阳离子在溶剂中受到较强烈的溶剂化,阴离子的溶剂化会变弱,     

Platinum(II) Diphosphinamine Complexes for the Efficient Hydration of Alkynes in Micellar Media

Highly active monomeric bis‐cationic platinum(II) catalysts bearing small bite angle diphosphinamine [N,N‐bis(diarylphosphino)amine] ‘PNP’ ligands efficiently catalyze Markovnikov hydration of terminal and internal alkynes to the corresponding ketones in water. Catalyst solubilization in water is achieved via ion pairing with anionic micelles formed by surfactant addition. The micelles ensure dissolution of apolar alkynes and promote the intimate contact between reagents and catalyst, while in organic‐water media in the absence of surfactants the reaction is sluggish. Hydration products can be isolated by means of extraction with an apolar solvent and the catalyst, that remains confined in the aqueous phase, can be recycled up to four times without loss of catalytic activity.     

Xanthate‐mediated polymerization of styrene on hyperbranched polyethylenimine: Synthesis,characterization, and guest‐encapsulating property

Hyperbranched polyethylenimine (HPEI) is a highly polar, multifunctional polymer bearing active amines throughout its globular structure. In this article, the amino protons, which were incompatible with living radical polymerization techniques, were alkylated with propylene oxide, leading to tertiary amines and hydroxyls, and part of the hydroxyl groups were further transformed into xanthate groups. The HPEI‐xanthate could mediate the polymerization of styrene, leading to a star‐like, multiarm amphiphilic polymer. It was found that the polymerization was a hybrid of living and conventional radical processes. The resulting amphiphilic, core‐shell‐structured polymer existed as a unimolecular micelle (UIM) in apolar solvent and could irreversibly encapsulate water‐soluble anionic dyes. At high pH, the encapsulated dyes could be partly released. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of interphase mixing on a water–organic solvent two-liquid phase microbial system: ethanol fermentation

Ethanol fermentation by Saccharomyces cerevisiae was investigated in broth-organic solvent two-liquid phase systems with and without interphase mixing. The effect of interphase mixing with aliphatic alcohols as polar solvents and with alkanes as apolar solvents was determined from investigations in three distinct systems: a solvent-saturated broth, a solvent-broth dispersion system and a dispersion-free solvent-broth system. Microbial activities, measured as a function of solvent volume and inoculum size, revealed that a dispersed polar solvent caused a longer growth lag time and a slower growth rate. Viability measurements showed that yeast cells were gradually killed in a dodecanol-water dispersion system and not in a dispersion-free one. This process was believed to be initiated and enhanced by cell adhesion to the solvent interface as observed under a microscope. Yeast activity was also measured as a function of an apolar solvent volume and inoculum size. A full fermentative activity was observed in an initially alkanesaturated broth unlike in an intermixed biphasic system. As a result of these investigations, it was concluded firstly that microbial activity in initially solvent-saturated broths with and without contact with a stagnant solvent phase can be different and secondly that the process efficiency of a biphasic bioreactor, unlike that of a chemical reactor, can be hampered by interphase mixing. The yeast activities in the presence of the various alcohols and alkanes were correlated with ‘log P’ values of the solvents. Full activity was observed at log P > 5 and almost none at log P < 4.     

纤维素-甲基丙烯酸丁酯的原子转移自由基聚合

以2-溴异丁酰溴为溴化剂,在离子液体([Amim]Cl)中与纤维素反应制备溴化纤维素大分子引发剂,以溴化纤维素/CuBr/N,N',N',N″,N″-五甲基二乙烯基三胺(PMDETA)为引发体系,N,N-二甲基甲酰胺(DMF)为溶剂,研究了甲基丙烯酸丁酯(BMA)的原子转移自由基聚合反应(ATRP)。合成了结构明晰的以纤维素为主链,聚甲基丙烯酸丁酯为支链的接枝共聚物Cellulose-g-PBMA。通过FTIR、1HNMR和GPC分别对大分子引发剂和接枝聚合物进行了分析。考察了聚合反应的活性特征,反应时间、催化体系、溶剂对聚合物相对分子质量(简称分子量,下同)及分子量分布的影响。结果表明,聚合反应转换率随时间呈线性增加,反应过程是活性可控聚合,催化剂和溶剂分别选用PMDETA/CuBr和DMF使反应更高效。     

Influence of montmorillonite on syndiotactic polymerization behavior of styrene

The influence of montmorillonite (MMT) on the syndiotactic polymerization behavior of styrene was studied. To avoid the hydrophilic surface of the MMT coming into contact with the catalyst, which could poison it, SAN was introduced between the MMT and Cp*Ti (OCH₃)₃. MMT was introduced into the catalytic system as a supporter for the Ti catalyst (supported catalytic system) or just dispersed in the polymerization solvent directly (in situ polymerization system). The polymerization results showed that surface modification of MMT dramatically affected the catalytic activity as well as the syndiotacticity of the polymers. This is mainly explained by the insulator SAN preventing the formation of the inactive/little active species Si? O? Ti and other atactic active species resulting from the reaction of the ? OH on the MMT layer surface with Cp*Ti(OCH₃)₃. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Epoxidation of cyclohexene over basic mixed oxides derived from hydrotalcite materials: Activating agent, solvent and catalyst reutilization

Synthesis and characterization of basic hydrotalcite-like derived catalysts were carried out and the resulting materials were tested in cyclohexene epoxidation. The reaction being dependent on the activating agent and the solvent of the reaction. Several nitriles and amides were used as activating agents and various compounds of different nature (protic and aprotic, polar and apolar) were analyzed as epoxidation solvents. The highest epoxide yield and cyclohexene conversion were achieved by using benzonitrile and methanol as activating agent and solvent, respectively. In the present work the reutilization of these solids in cyclohexene epoxidation has been tested by regeneration. The catalyst washed with the solvent after one reaction did not enhance the catalytic properties of the fresh solid. Nevertheless the activation of the solid up 600 °C provided a good activity after four runs.     

钕系异戊二烯聚合稀土催化剂活性的研究

从催化剂各组分的电导率、催化剂陈化方式和各组分不同配比对聚合活性的影响3个方面研究了在25℃加氢汽油介质中,钕系稀土催化体系Nd(i-octa)_3-Al(i-Bu)_3-CCl_4用于聚合异戊二烯的活性。结果表明,催化剂三组分间的反应是CCl_4与Al(i-Bu)_3先作用生成氯化异丁基铝再向钕盐提供卤素形成活性中心,活性中心具有双金属络合物结构。催化剂在(Cl+Al)+Nd陈化方式下活性最高,各组分最佳配比为Nd/Al/Cl=1/50/3。     

Novel monotitanocene and methylaluminoxane catalyst for syndiospecific polymerization of styrene

Syndiotactic polystyrene (sPS) was synthesized with a novel monotitanocene complex of η⁵‐pentamethylcyclopentadienyltri‐4‐methoxyphenoxy titanium [Cp*Ti(OC₆H₄OCH₃)₃] activated by methylaluminoxane (MAO) in different polymerization media, including heptane, toluene, chlorobenzene, and neat styrene. In all cases bulk polymerization produced sPS with the highest activity and molecular weight. Solution polymerization produced much better activity in heptane than in the other solvents. Using a solvent with a higher dipole moment, such as chlorobenzene resulted in lower activity and syndiotacticity because of the stronger coordination of solvent with the Ti(III) active species, which controlled syndiospecific polymerization of styrene. With bulk polymerization at a higher polymerization temperature the Cp*Ti(OC₆H₄OCH₃)₃–MAO catalyst produced sPS with high catalytic activity and molecular weight. The external addition of triisobutylaluminum (TIBA) to the Cp*Ti(OC₆H₄OCH₃)₃–MAO system catalyzing styrene polymerization led to significant improvement of activity at a lower Al:Ti molar ratio, while the syndiotacticity and molecular weight of the yields were little affected. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1243–1248, 2001     

Computational Analysis of the Solid-State and Solvation Properties of Carbamazepine in Relation to its Polymorphism

The solvent-dependent polymorphism of the active pharmaceutical ingredient (API) carbamazepine is interpreted from calculations of the solid-state and API-solvent intermolecular interactions. These simulations suggested that apolar solute-solute interactions could be disrupted by apolar solvents. In contrast, the polar solute-solute interactions were found to be easily disrupted by polar and protic solvents. This is consistent with experimental observations that the crystallization of the metastable form II is more dominant in apolar solvents. The Mercury program remains the gold standard in terms of usability; however, further expansion into more complex simulation techniques could make this package of even greater use in pharmaceutical manufacturing workflows.     

Accelerated weathering and chemical resistance of polyurethane powder coatings

A study of the weathering mechanism of innovative polyurethane powder coatings has been performed. UV-B irradiation and condensation cycle accelerated tests were carried out on two different polyurethane powder coating formulations for outdoor applications. Using Fourier transform infrared spectroscopy and microscope observation, it was possible to analyze the photochemical and morphological modifications. In addition, the color and gloss changes were measured. Organic coatings are often in contact with solvents in particular during cleaning actions. The chemical resistance was then studied considering the evolution of the corrosion barrier property of the coating as a function of the solvent contact time. Electrochemical impedance spectroscopy measurements were carried out. Methylethylketone (polar) and xylene (apolar) were considered as representative solvents. Due to the strong polarity, the first solvent showed a strong interaction with the hydrogen bonds between the polyurethane chains causing the solvent uptake. The amount of solvent uptake depends on the coating chains rigidity caused by the different polyester resin monomers. The apolar xylene presented no significant interaction with the coatings.