疏水链段对两亲性三嵌段共聚物在水中聚集行为的影响

以结构明确的两端为短的聚苯乙烯(PS)或聚甲基丙烯酸甲酯(PMMA)链段,中间为长的聚乙二醇(PEG)链段的PS-b-PEG-b-PS和PMMA-b-PEG-b-PMMA两亲性三嵌段共聚物为对象,研究了PS和PMMA链段对其在水中形成胶束和凝胶的影响.两种三嵌段共聚物在水中形成以PS或PMMA链段为核、PEG链段为壳的球形胶束,流体力学半径Rh,app为15.3~24.3 nm,并随PEG链段长度增长而增大.临界胶束浓度CMC均小于0.01 mg/mL,随着PS和PMMA链段长度的增加而减小.PS-b-PEG-b-PS浓度高于4.5 wt%可形成较强的疏水缔合的物理凝胶,平衡模量Ge可达到103Pa;PMMA-b-PEG-b-PMMA浓度高于7.5 wt%可以形成弱的凝胶,Ge<10 Pa.凝胶的储存模量G′和损耗模量G″均随着PS或PMMA链段的增长而增大.     

双亲嵌段共聚物PSt-b-PAA在甲苯中的自聚集行为

以α-溴乙苯为引发剂,溴化亚铜为催化剂,2,2'-联吡啶为配体,用原子转移自由基聚合(ATRP)法合成了结构一定的嵌段共聚物聚苯乙烯-b-聚丙烯酸丁酯(PSt-b-PBA).经水解制备了双亲性嵌段共聚物聚苯乙烯-b-聚丙烯酸(PSt-b-PAA);采用单溶剂溶解法配制了PSt-b-PAA在甲苯中的反胶束溶液;以极性荧光化合物N-1-萘乙二胺盐酸盐(NEAH)为极性微区探针,用荧光光谱法并配合透射电镜观察探索了双亲嵌段共聚物PSt-b-PAA在甲苯溶液中的自聚集行为,考察了双亲性嵌段共聚物浓度、链结构及温度等因素对反胶束化行为的影响规律.结果表明,亲水链PAA短而亲油链PSt长的双亲嵌段共聚物PSt-b-PAA,用单溶剂溶解法可使其在甲苯中发生自聚集,形成以亲水段为核,疏水段为壳的星状反胶束结构;反胶束为10-20nm的球形聚集态结构;PSt-b-PAA的自聚集行为及临界胶束浓度与分子链的微结构和温度等因素相关,且随着共聚物浓度的增大,小胶束会逐渐结合形成大的纺垂状聚集体.     

PS-PMMA嵌段共聚物/PMMA在选择性溶剂中的自组装行为

用动态光散射和透射电镜研究了嵌段共聚物聚苯乙烯-聚甲基丙烯酸甲酯(PS-b-PMMA)和其对应的均聚物聚甲基丙烯酸甲酯(PMMA)在选择性溶剂四氢呋喃/环己烷(THF/CYH)中的自组装行为.选择性溶剂对PS嵌段是良溶剂,对PMMA嵌段和均聚物PMMA是非良溶剂,实验结果表明,在适当的分子量及组成条件下,PS-PMMA/PMMA在选择性溶剂中形成了单分散的纳米胶束,均聚物PMMA与PMMA嵌段一同形成了胶束的核,通过控制均聚物PMMA的量可以在较大的范围内调整胶束的尺寸.     

聚苯乙烯-聚甲基丙烯酸甲酯两嵌段共聚物薄膜在丙酮蒸汽退火下的形貌演化

用敲击模式原子力显微镜研究了聚苯乙烯-聚甲基丙烯酸甲酯(PS-b-PMMA)两嵌段共聚物薄膜形貌在丙酮蒸汽退火下随时间的演化过程.对于对称的嵌段共聚物薄膜(fPS≈fPMMA,fPS为PS-b-PMMA中PS的体积分数,fPMMA为PMMA的体积分数),通过控制膜厚和平衡态时相周期的比值可以使不同分子量的嵌段共聚物薄膜都实现由蠕虫状结构到孔洞再到条纹的形貌演化过程;对于非对称的嵌段共聚物薄膜,发现当聚苯乙烯组分含量较少(25%,36%)时,薄膜的形貌由无序态分别转变为规则排列的小球和直接转变为条纹结构;而当聚苯乙烯组分含量较多(70%)时,薄膜的形貌则由无序态转变为较平整的表面结构.我们对不同形貌的形成机理进行了详细的讨论.     

多嵌段共聚物(P4VP-b-PS-b-P4VP)_n的胶束化行为研究

研究了一系列具有不同链段长度和组成的聚4-乙烯基吡啶-聚苯乙烯-聚4-乙烯基吡啶多嵌段共聚物(P4VP-b-PS-b-P4VP)n在其选择性溶剂甲苯和pH<3的水中的胶束化过程,主要研究了多嵌段共聚物链段长度、溶液浓度和溶剂对其胶束形态的影响.透射电镜和原子力显微镜结果表明随着P4VP段链的相对增长,多嵌段共聚物在甲苯中的胶束形态由蠕虫链状向短棒状到球状胶束变化,而其在pH<3的水溶液中均形成球形胶束.由于特殊的链结构,聚合物的浓度对(P4VP-b-PS-b-P4VP)n多嵌段共聚物的胶束行为和胶束形态有着重要的影响.同时,(P4VP-b-PS-b-P4VP)n多嵌段共聚物分子量分布的多分散性对其在选择性溶剂中的胶束形态也有所影响.     

AB型聚乙二醇单甲醚-聚(L-丙氨酸)嵌段共聚物自组装过程的核磁共振研究

利用核磁共振方法研究了AB型双嵌段共聚物(MPEG45-b-PA32)在选择性溶剂中的自组装行为及胶束化过程.嵌段共聚物在三氟乙酸中聚氨基酸和聚乙二醇链段均处于自由运动状态,聚丙氨酸链段为无规线团结构.在向该溶液中逐渐加入氘代水的过程中,聚丙氨酸链段又重新聚集形成规整的二级结构.结合1H-NMR和COSY谱分析,结果显示这一自组装过程伴随着聚(L-丙氨酸)链段由无规线团向α-螺旋结构的构象转变,同时嵌段共聚物逐渐形成核-壳型胶束结构.利用透射电镜观察了所形成胶束的形态,嵌段共聚物主要形成粒径150 nm到220 nm的球形胶束.     

荧光标记法研究双嵌段共聚物的胶束化行为

结合Forster能量转移和芳香分子极性标尺技术,研究了两端分别标记芴和芘基团、具有不相容双嵌段的共聚物(Fl-PMMA400-b-PAA80-Py)的胶束化行为。结果表明,在临界胶束浓度以下,较长的PMMA链段首先形成寡链聚集体,这一现象反映了具有不相容双嵌段的共聚物胶束化特征;此外,本文首次发现芴基团荧光对其微环境极性较为敏感。     

分子水平研究不同嵌段结构苯乙烯/丁二烯共聚物的表面结构

利用具有准单分子层灵敏度的和频振动光谱(SFG)、原子力显微镜(AFM)和接触角(CA)测定技术研究链结构和溶剂对苯乙烯(S)/丁二烯(B)嵌段共聚物表面准分子层化学结构形成的影响.结果表明,两嵌段共聚物SB比三嵌段共聚物SBS更有利于聚丁二烯(PB)组分在膜表面富集.利用PB的选择性溶剂环己烷做溶剂时,SB膜表面层完全由纯的PB组分组成,而SBS表面则是聚苯乙烯(PS)与PB二组分共存.利用PS的选择性溶剂甲苯做溶剂时,SB与SBS表面都是PS与PB二组分共存,其中SBS表面PS组分的含量更高.原因是由于溶剂影响嵌段共聚物分子在溶液中的构象从而影响溶剂挥发后聚合物表面结构的形成.     

聚L-丙氨酸-聚乙二醇嵌段共聚物的胶束化行为研究

以氨基聚乙二醇单甲醚(MPEG-NH₂)为大分子引发剂, 采用开环聚合方法合成了聚L-丙氨酸-聚乙二醇嵌段共聚物(PAME), 并对其结构进行了表征; 用圆二色谱(CD)研究了嵌段共聚物在水溶液中的二级结构, 用芘荧光探针技术研究了共聚物胶束的形成及其临界胶束浓度(CMC), 利用动态光散射(DLS)和透射电镜(TEM)研究了胶束的粒径分布和形态. 结果表明, 在水溶液中共聚物链以α-螺旋构象形式存在, 在一定条件下嵌段共聚物能够形成球形的稳定胶束, PAME-1形成胶束的CMC为1.99×10^-5 mol/L, CMC值受共聚物中聚L-丙氨酸(PLA)链段含量的影响.     

四臂星型聚苯乙烯-聚4-乙烯基吡啶嵌段共聚物纤维状胶束及负载金纳米粒子的研究

通过两步原子转移自由基聚合,制备了4种不同嵌段长度的四臂星型嵌段共聚物苯乙烯-聚4-乙烯基吡啶嵌段共聚物(PS-b-P4VP)4.在选择性溶剂甲苯中,随着嵌段长度的变化,自组装胶束的形态从球型到短棒状和纤维状的转变,其中(PS25-b-P4VP90)4自组装形成的以P4VP为核,以PS为花瓣型壳的纤维状胶束.以这种纤维状胶束作为模板,制备了金纳米粒子均匀分布的一维纳米材料     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.