在四官能团引发剂存在下的自缩合乙烯基聚合反应制备丙烯酸酯类超支化共聚物

超支化聚合物具有特殊的结构和性能 ,可通过一步法聚合直接制得 ,具有大规模工业应用前景 .近年来 ,超支化聚合物的研究已成为高分子科学的热门课题之一[1～ 3 ] .超支化聚合物的一个主要缺点是它的分子量分布比较宽 .Ｍ櫣ｌｌｅｒ[4] 等通过理论计算指出 ,在聚合体系中加入ｆ个功能基团的分子Ｂｆ[对自缩合乙烯基聚合反应 (ＳＣＶＰ) ,Ｂｆ为ｆ个引发基的引发剂 ;对ＡＢｘ 型单体的缩聚反应 ,为有ｆ个Ｂ官能团的分子 ],可以降低超支化聚合物的分子量分布 ,这一结果已被实验证实[5～ 7] .我们用ＭｏｎｔｅＣａｒｌｏ方法模拟了在多官能团引…     

单体慢加入技术对超支化聚合物分子参数的影响

详细分析了单体慢加入到多官能度核分子中制备超支化聚合物的动力学过程,以单体转化率为参数导出了产物的聚合度分布函数、平均聚合度、多分散性指标和支化度等分子参数的解析式,计算结果与文献报道的实验数据十分一致.分子参数依赖于核的官能度(f)、核分数(α)和单体转化率(x),这为通过聚合反应条件来进行分子结构的设计提供了理论依据.与一步聚合方法的产物相比,单体慢加入技术能够改进产物的分子量分布,提高其支化度.     

AB_g型单体超支化聚合反应的理论模型

超支化聚合物的可控制备与分子设计对其工业化应用是十分重要的,这有待于弄清超支化聚合物的形成机理.本文回顾了早期关于超支化聚合物的Flory-Stockmayer理论,重点介绍与ABg型单体相关的超支化聚合反应的动力学原理,这是我国科学家在这一领域的工作亮点,在国际上受到了广泛的关注.相比其它一些理论方法,聚合反应动力学理论原理清晰,可通过解动力学微分方程导出反应产物的平均支化度和聚合度分布函数的解析式,由此可以计算各种分子参数,为超支化聚合物的分子设计和可控制备提供了理论基础.     

超支化聚合物制备方法的研究进展

超支化聚合物是一类可以通过一步法来合成的具有高度支化结构的体型大分子.经过二十年的研究,超支化聚合物由于其独特的结构和性能特点以及可实现规模化生产的特点, 已经迅速成为一类重要的和具有广阔应用潜力的高分子材料.本文从单体类型的角度介绍了超支化聚合物的主要制备方法及其发展历程,主要涉及ABx型,AB*型,A2 B3型以及潜在ABx型单体(包括开环聚合和偶合单体法)等,同时论述了各制备方法的优点和局限性 .     

AB_2型β-环糊精功能单体及其水溶性超支化聚合物的合成与表征

为了得到结构确定的β-环糊精大单体并用于超支化聚合,通过对β-环糊精上6位伯羟基和2位仲羟基的多步功能化改性得到了同时含有Si—H和—CH CH2基团的AB2型β-环糊精大单体,并利用硅氢加成反应一步法合成了一种新型的水溶性超支化聚合物,其具有β-环糊精空腔和超支化空穴两种疏水单元,从而可构建出一种新颖的超分子体系.采用1H-NMR、13C-NMR、飞行时间质谱和元素分析对AB2单体及其聚合物的结构进行了表征.结果表明,单体和聚合物的结构与所设计的分子结构相符合.凝胶渗透色谱/多角度激光光散射(SEC/MALLS)联用仪测得该聚合物的数均分子量、分子量分布及特性黏数分别为36690、1.887和15.8mL/g.     

骨架可水解的具核超支化聚缩醛的合成与表征

通过AB2型聚合单体4-(2-羟基乙氧基)苯甲醛二甲缩醛与B2型核分子苯甲醛二甲缩醛的缩醛转移聚合反应,反应过程中不断排出低沸点的醇,合成了具核、骨架可水解的超支化聚缩醛(HBPAs).实验表明,HBPAs的分子量,多分散性和聚合度随着核比例的改变发生明显的变化.增加核比例,聚合物的分子量,多分散性和聚合度均降低.HBPAs在弱酸性条件下,骨架发生水解,生成4-(2-羟基乙氧基)-苯甲醛.研究发现,核比例对于聚合物降解速率有明显的影响,增加核比例,聚合物的降解速率加快.这表明,通过加入核分子,可以在一定程度上调控超支化聚缩醛的结构与性能.     

两亲性超支化聚合物的研究进展

两亲性超支化聚合物作为一种新型功能性材料.近年来引起了人们的广泛关注.两亲性超支化聚合物的合成丰要是利用不同亲水性的链段对超支化聚合物端基进行改性,或者首先在超支化聚合物末端产生活性位点,再利用超支化分f作为大分子引发剂引发烯类单体进行斤环聚合、原子转移自由基聚合等得到以超支化聚合物为核的两亲性超支化共聚物;这些分子由...     

超支化聚合物的合成和自组装研究

超支化聚合物作为树形聚合物的一种,具有独特的结构和性能,受到了科学界和工业界的广泛关注.本文简要总结了研究者们在超支化聚合物的合成、组装及应用方面的部分工作成果.主要包括以下3方面的内容:第一部分介绍了超支化聚合物的合成方法;第二部分介绍了超支化聚合物多维多尺度的自组装结构和组装机理,包括纳米球形胶束,纳米、微米级囊泡,大的复合囊泡,纳米纤维,纳米、微米及宏观管和多孔膜等;第三部分介绍了超支化聚合物在生物医药、细胞模拟及纳米粒子模拟制备等方面的应用.     

三元非等活性自缩合乙烯基聚合体系的Z均回转半径

利用Monte Carlo模拟方法研究了由单体、引发单体和引发核组成的三元自缩合乙烯基聚合反应体系. 重点考察了两类活性基团反应活性的差异、引发单体分数、引发核的配比及活性基团数等因素对体系中无核和有核两类超支化高分子Z均回转半径的影响. 结果表明, 这些因素对超支化高分子的结构和尺度影响显著, 因而通过调节有关参数可以实现对超支化高分子结构和尺度的调控.     

超支化聚合物研究进展

超支化聚合物由于具有高度文化三维球状结构以及众多的端基,因此显示出与相应线型分子截然不同的性质,如低粘度、无链缠结和良好的溶解性.本文讨论了超支化聚合物的特性与表征,对合成超支化聚合物所用单体以及产物作了详细介绍,旨在引起对该领域的兴趣.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.