用NMR分析可生物降解的两亲性嵌段共聚物的相对分子质量和组成

凝胶渗透色谱(GPC)法是根据聚合物分子链流体力学体积大小的比较来测定聚合物相对分子质量(以下简称分子量)的,测得的聚合物分子量与聚合物分子链在溶剂中的构象有关[1]。两亲性嵌段共聚物分子链中亲水链段和亲油链段的极性差异很大,几乎在任何溶剂中它们的构象都不相同,因此可     

聚肽分子链构象转变研究

聚肽分子链在一定的条件下可发生右旋分子链构象与左旋分子链构象间的构象转变 .文中提出了一个有关这一现象的统计理论解释 ,理论包含了两个重要的参数γ、ρ .γ与右旋和左旋分子链构象间能量差别有关 ;ρ与在左旋分子链段中启始一个右旋构象的结构单元所需能量有关 .进一步考虑了体系中酸分子存在对构象转变的影响 ,以解释新近发现的聚肽左、右旋多重分子链构象转变现象 .此外 ,运用核磁共振 (NMR)手段还对这一现象做了进一步的研究 .通过与实验结果和文献中报告的数据比较 ,证明这一理论可以很好地解释聚肽分子链中发生的左、右旋分子链构象转变     

介电松弛谱法用于高分子链动力学行为的研究

介电松弛谱法是研究高分子链松弛运动的一种有效方法.它可反映出分子的特征结构信息,对揭示高分子链动力学行为的本质及规律、调控其凝聚态结构意义重大.本文从介电松弛谱理论出发,总结出几种常用的介电特征参数以及用于解析这些参数的数学模型.通过介电松弛谱中高分子链的弛豫过程的解析,可得出与高分子链运动相关的特征参数,如介电常数、介电松弛强度以及链运动的特征松弛时间,从而判断链松弛运动的尺寸小大,松弛的基团以及链运动的协同过程;还可与Arrenius方程、Vogel-Tammann-Fulcher（VFT）方程、统计学模型建立联系,获得界面构造、分子内部组成、链动力学行为同环境的依存性等信息,为高分子材料的分子设计、开发与应用奠定高分子物理理论基础.     

高聚物的分子聚集态结构

高聚物结构按其研究单元的不同可分为二大类:一为分子内的结构,是研究一个分子链中原子或基团之间的几何排列,即高聚物的链结构。另一为分子间的结构,是研究单位体积内许多分子链之间的几何排列,即高聚物的分子聚集态结构,也称为超分子结构。高聚物链结构是决定高聚物基本性质的主要因素,各种     

聚亚苯基苯并二噻唑的X射线衍射研究

本文用X射线衍射研究了聚亚苯基苯并二噻唑(PBT)薄膜的结构特征。衍射结果表明PBT在液晶态成膜具有高的取向度,分子链在垂直于取向方向呈有序的二维周期排列,沿取向方向分子链相互间无序平行排列。热处理可明显提高PBT的有序度,即在垂直于取向方向分子链的二维排列更规整,晶格畸变减小,而取向方向分子链中苯杂环呈群集排列,出现三维有序的衍射斑点,测其群集结构平面的法线与取向方向夹角为29°。     

不同溶液条件下瓜尔胶的分子链形态

本文利用原子力显微镜(AFM)和动态光散射(DLS)对瓜尔胶的分子链形态进行了表征。瓜尔胶稀溶液中大量存在的分子链聚集体表明分子链聚集是一种趋势。聚集的程度跟分子链间作用是密切相关的。加碱或适量尿素有利于瓜尔胶破坏分子链间作用,降低了分子链聚集体的尺寸,使分子链更为舒展而相互穿插,这有利于形成更为致密的三维网络链结构,导致粘弹性增加。     

Gemini表面活性剂:联接链在自组织中的作用及意义

本文总结了Gemini表面活性剂分子结构中联接链在其自组织过程中所发挥的独特作用,这主要来自联接链长度和刚柔性两方面的效应,这些效应综合导致了Gemini分子两条烷烃尾链的协同作用、头基电荷密度改变、分子几何变化以及由此决定的多样化聚集体结构及形貌等。更具体地讲,柔性联接链主要依赖不同长度影响分子的上述功能。过长的联接链还可能通过自身弯曲来适应环境,从而影响分子自组织。短刚性联接链的效应等同于类似长度的柔性联接链,而长刚性联接链由于阻碍了两条烷烃尾链的靠拢,产生了两个突出特征:分子呈似柱形状以及同等几率的两条尾链沿联接链顺式或反式排列构型。这使得长刚性联接链分子在低浓度时就可形成网状聚集体,增加浓度或少量添加剂干扰易转变成低表面曲率的线状胶束或囊泡。适合条件还可催生少量反式构型分子,它们将一条烷烃尾链伸出聚集体外,通过疏水相互作用串接相邻的聚集体。本文也讨论了对联接链进行的化学修饰,这有望促进分子的自组织活性,或者赋予聚集体某种新的特殊功能。列举的例子很好表明了Gemini分子结构的独特性,以及Gemini表面活性剂复杂的自组织行为和多样化的聚集结构。     

用辐射交联方法估算聚合物的分子链内旋转位阻因子

作为一种结构参数,聚合物的分子链内旋转位阻因子可表征聚合物分子链的柔顺性,并与聚合物的许多物理性质相关联。过去实验事实表明,聚合物的辐射交联行为与其分子链柔顺性密切相关。本工作从这一结论出发,研究聚合物的分子链内旋转让阻因子(σ)与其交联参数β之间的关系,为估算聚合物σ值提供一种新方法。     

含氟聚合物分子链的构象和柔顺性

通过对含氟聚合物分子链内旋转构象的分析,发现含氟聚合物与其它结构类型的聚合物一样,其玻璃化转变温度Tg与分子链横截面积A和分子链内旋转让阻因子σ之间的关系遵循同样的规律^[1,2]。建议用Tg=973(σ-1.44)来计算含氟聚合物的分子链内旋转位阻因子。内旋转位阻因子相同时,含氟聚合物的玻璃化转变温度较其它结构类型的聚合物为高(图2),可归结为含氟聚合物分子链的紧密堆积。     

偶氮苯衍生物自组装单分子膜中的分子取响

利用反射红外光谱研究了金表面一系列具有不同碳链长度的偶氮苯巯基衍生物的自组装单分子膜.通过对比各向同性样品的透射谱和单分子膜的反射谱中各个吸收峰强度,定量地研究了分子中各部分的取向与分子结构的关系.我们分别提出了烷基链和偶氮基团取向计算的方法,利用该方法成功地求得了分子中各部分在膜的倾角.结果显示,当分子中烷基链长度增大时,碳链和偶氮苯基团相对于法线的倾斜逐渐加剧.这种倾角的变化归因于分子中碳链间范德华引力增大时,引起分子逐渐倾斜以达到最佳的范德华接触.同时研究发现,烷基链和偶氮基团受碳长度变化的影响并不相同.当分子中亚甲基数目增多时,烷基链的倾角迅速增大而偶氮苯倾角的增大则相对缓慢,这反映了它们在空间需求和本身刚性上的不同。     

New type of thermoplastic multiblock elastomers––poly(ester-block-amide)s––based on oligoamide 12 and oligoester prepared from dimerized fatty acid

Multiblock poly(ester-block-amide)s (PEA) elastomers comprising hard blocks of oligoamide and oligoester soft segments were prepared and their structure-property relations were analysed. The polycondensation reaction of oligoesters (prepared from 1,4-butanediol and dimerized fatty acid) with oligolaurolactam (PA12) gave copolymer series with variable blocks content (the soft segments content was varied from 24 to 60 wt.%). PEAs are the phase system composed of crystallised sequences of oligoamide (hard segment phase) as well as oligoesters (soft segment phase). Mixing between the hard and soft phases was studied by thermal and mechanical measurements (DSC, DMTA). These results have indicated on a multiphase structure of investigated materials. The relationship between the observed thermal and tensile properties and the soft/hard segments content indicated on an increase of the phase separation with soft segments content.     

Preparation of oligoamide‐ended poly(ethylene glycol) and hydrogen‐bonding‐assisted formation of aggregates and nanoscale fibers

An oligoamide‐ended poly(ethylene glycol) (PEG) with a PEG weight‐average molecular weight of 5000 (PEG‐5000‐oligoamide), with 3,5‐bis‐[2‐(5‐acetylamino‐2‐isobutoxy‐benzoylamino)‐acetylamino]‐benzoyl as the oligoamide, was synthesized. PEG‐5000‐oligoamide aggregated in chloroform or toluene via hydrogen‐bonding interactions among the oligoamide strands as a core and PEG, which was soluble in the solvents, as a shell. When a chloroform solution of PEG‐5000‐oligoamide at a concentration of approximately 0.06 g/L was cast onto a silicon wafer or a mica plate, rapid solvent evaporation induced its self reassembly as nanofibers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1119–1128, 2005     

Design and Synthesis of a Highly Stable Six-hydrogen-bonded Self-assembly Yellowish Green Electroluminescent Molecular Duplex

Since the first fabrication of thin-layer organic electroluminescent(OEL)device in1987by C.W.Tang et al1.,OEL materials had been of ever increasing interest2,3.While up to now,full-color display has been commercialized with small molecules having different structures.In general,host-dopant systems are often employed in RGB OLEDs.This procedure,however,would lead to relatively poor performance for OEL devices,because of the easy aggregation and crystallization of the dopants,which would…     

一种带有吡唑啉侧链的低聚酰胺的合成

A oligoamide with pyrazoline segment was designed and synthesized.Its structure was identified by IR,MS and 1HNMR.Fluorescence property of the target compoud in solution(DMF) was studied.The results showed that the strongest emission peak was at 442nm and the half peak width was 64nm and the fluorescence quantum yield(Φ) was 73.9%,which enhanced 13% compared to the simple pyrazoline structural unit's Φ.     

High-Affinity Hybridization of Complementary Aromatic Oligoamide Strands in Water

We prepared a series of water-soluble aromatic oligoamide sequences all composed of a segment prone to form a single helix and a segment prone to dimerize into a double helix. These sequences exclusively assemble as antiparallel duplexes. The modification of the duplex inner rim by varying the nature of the substituents borne by the aromatic monomers allowed us to identify sequences that can hybridize by combining two chemically different strands, with high affinity and complete selectivity in water. X-ray crystallography confirmed the expected antiparallel configuration of the duplexes whereas NMR spectroscopy and mass spectrometry allowed us to assess precisely the extent of the hybridization. The hybridization kinetics of the aromatic strands was shown to depend on both the nature of the substituents responsible for strand complementarity and the length of the aromatic strand. These results highlight the great potential of aromatic hetero-duplex as a tool to construct non-symmetrical dynamic supramolecular assemblies.     

Sequence-specific association in aqueous media by integrating hydrogen bonding and dynamic covalent interactions

Oligoamide strands that associate in a sequence-specific fashion into hydrogen-bonded duplexes in nonpolar solvents were converted into disulfide cross-linked duplexes in aqueous media. Thus, by incorporating trityl-protected thiol groups, which allows the reversible formation of disulfide bonds, into the oligoamide strands, only duplexes consisting of complementary hydrogen-bonding sequences were formed in aqueous solution as well as in methanol. The sequence-specific cross-linking of oligoamide strands was confirmed by MALDI-TOF, reverse-phase HPLC, and by isolating a cross-linked duplex. This study demonstrates that the sequence-specificity characteristic of multiply hydrogen-bonded systems can be extended into competitive media through the interplay of H-bonding and reversible covalent interactions, based on which a new class of molecular associating and ligating units that are compatible with both polar and nonpolar environments can be conveniently obtained.     

Development of an oligoamide coating as a surface mimetic for aromatic polyamide films used in reverse osmosis membranes

We developed a method for the in situ synthesis of an oligoamide coating on gold. The resultant surface chemical composition, wettability, and chemical nature were comparable to aromatic polyamide films used as reverse osmosis membranes. Hence, the oligoamide wafer may be used in adsorption/fouling studies as a surface mimetic of reverse osmosis membranes.     

Synthesis of a new organogelator based on block structures of co‐oligoamide‐6

A series of new bisurea derivatives having in common two co‐oligoamide arms have been synthesized and characterized by NMR, SEC, DSC, SEM, and optical microscopy. These compounds are only soluble at high temperature in aprotic polar solvent. By cooling the solutions, gelation occurs if the concentration of these bisurea derivatives is higher than 3% (w/w). Comparisons with derivatives devoid of oligoamide arms leading no gelation suggest that two kinds of interaction are necessary to get the self‐assembling, namely intermolecular hydrogen‐bonding between urea groups and between oligoamide arms. As these interactions induce interconnections in several directions, the possibility of building the long classical fibrous structures is limited. Accordingly, the ultrastructure of the gel consists only of short interconnected fibers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4122–4129, 2008     

Melting behavior of poly(oxytetramethylene)-<Emphasis Type="Italic">alt</Emphasis>-(aromatic oligoamide) block copolymers

Using temperature-modulated differential scanning calorimetry, the melting behaviour of poly(oxytetramethylene)-alt-(aromatic oligoamide) (POTM-alt-AOA) has been studied in comparison with that of polyoxytetramethylene glycohols (POTMGs). The apparent melting temperature of the block copolymers is found to be less than that of the corresponding POTMGs by approximately 30°C. The relaxation time of melting of a POTM segment has been estimated and compared with that of POTMG. The relaxation time of POTM-alt-AOA is slightly shorter than that of POTMG when the molar mass of the POTM segment is 2900; however, it is longer when the molar mass is 1400.     

Synthesis of a crescent aromatic oligothioamide and its high selectivity in recognizing copper(Ⅱ) ions

Functionalization of shape-persistent aromatic oligoamides still represents a difficult task nowadays. A crescent aromatic oligothioamide was synthesized by simple thionation of the corresponding oligoamide with the Lawesson's reagent. The results from UV-vis spectra of the molecule upon metal ion complexation demonstrated its higher selectivity in recognizing Cu2+ ions compared to the oligoamide precursor. The stoichiometry of the complex formed between the thioamide and Cu2+ was found to be 1:1 with a binding constant of (4.3±0.9)×104 mol/L.