固体NMR考察有机硅聚合物的热解过程

应用²⁹Si和¹³C固体NMR方法考察了几种有机硅聚合物前驱体热解制备SiC陶瓷的过程,通过²⁹Si和¹³C NMR谱分析了热解产物的结构.结果表明聚碳硅烷及其氧化交联聚合物前驱体在高温下的热解可以获得SiC陶瓷相.     

2,6-双(三甲基锡)-4,8-双(2-乙基己氧基)苯并[1,2-b∶4,5-b']二噻吩的合成与多核NMR研究

以苯并[1,2-b∶4,5-b´]二噻吩-4,8-二酮为原料合成了一种聚合物太阳能电池材料的单体2,6-双(三甲基锡)-4,8-双(2-乙基己氧基)苯并[1,2-b∶4,5-b´]二噻吩. 通过多核1D和2D NMR技术（包括1D ¹H、¹³C、¹¹⁹Sn、¹¹⁷Sn NMR、DEPT、选择性1D TOCSY及2D¹H-¹H COSY、gHSQC、gHMBC）表征了目标分子结构,完成了 ¹H、¹³C、¹¹⁹Sn 与¹¹⁷Sn NMR化学位移归属,并探讨了该化合物的NMR谱线特征.     

盐酸马尼地平的核磁共振数据解析

盐酸马尼地平是第三代合成降压新药．本文利用一维、二维核磁共振（NMR）技术,包括¹H NMR、¹³C NMR DEPT-135、¹H-¹H NOESY、¹H-¹H COSY、¹H-¹³C HSQC和¹H-¹³C HMBC,对其¹H和¹³C NMR信号进行了全归属,进一步确证了其分子结构．同时,对其¹H NMR和¹³C NMR谱中一些异常信号进行了讨论．     

核磁共振技术在生物质转化中的应用

生物质结构的精确分析研究有利于其各个组分的转化利用,而核磁共振（NMR）技术是生物质解聚及结构演变分析中重要的表征技术.本文主要介绍了¹H NMR、¹³C NMR、³¹P NMR和2D HSQC四种NMR技术在生物质结构、产物定性和定量分析、反应路径和催化解聚机理探究中的应用,然后讨论了NMR技术应用于生物质研究中存在的主要问题,并进行了展望.     

丝光沸石催化剂的固体高分辨核磁共振研究

利用²⁹Si MAS NMR及²⁷Al MAS NMR技术研究了丝光沸石催化剂制备过程中的结构变化,并利用Al的四极作用大小来区分重叠在一起的不同的Al物种.     

β-苯甲酰基-γ-取代苯基-γ-丁酸内酯的NMR研究

利用¹H NMR,¹³C NMR,2DNMR及IR,MS等技术对β-苯甲酰基-γ-取代苯基-γ-丁酸内酯的结构及空间构型进行确证,讨论了该结构的NMR谱学行为,提出了生成该化合物的可能的化学反应历程.     

拉伸取向聚合物2H NMR谱的键涨落模型Monte Carlo模拟

采用三维键涨落模型（BFM）的Monte Carlo计算机模拟方法,模拟了两种分别具有高取向和低取向链微观结构的拉伸取向聚合物²H NMR谱. 讨论了排除体积效应与链的均方末端距分布对²H NMR谱线的影响. 结果表明,排除体积效应对高取向和低取向聚合物²H谱劈裂的影响是不同的,较小均方末端距的链决定²H谱劈裂,而较大均方末端距的链使²H谱产生长的拖尾. 采用BFM计算机模拟与²H NMR实验的结合是研究拉伸取向聚合物网络微观结构的有力手段.     

圆果皂甙元的NMR和构型研究

本文利用了多种NMR技术,其中包括¹H ¹³C NMR,DEPT、COSY、C,H-COSY、COLOC和NOE差谱,首次确定了圆果皂甙元的结构及构型。     

含手性膦配体的铑化合物的NMR研究

利用1D和2D NMR技术.对含有手性膦配体的铑化合物trans-((3-MBPA)₂Rh(CO)Cl)(1)和trans-((2-MBPA)₂Rh(CO) Cl)(2),进行¹H和¹³C NMR谱分析,归属了所有的¹H和¹³C NMR谱线,并根据磷和铑的偶合常数及羰基与磷,铑的偶合常数确定它们是反式构型.     

氨基酸合成方法研究-(XI)N-取代亚氨酸酯与芳醛缩合产物-去氢氨基酸衍生物的构型及其NMR研究

通过¹H NMR、NOE差谱和门控去偶¹³C NMR等的研究确定了新合成的五对α-去氢氨基酸衍生物的构型,并利用部分弛豫、APT ¹³C NMR二维碳氢相关谱及¹³C-¹⁹F偶合常数等对NMR谱线进行了归属.     

A new hyperbranched star polyether electrolyte with high ionic conductivity

Hyperbranched poly(glycidol) containing hydroxyl groups was firstly synthesized via anionic polymerization and then reacted with 2-bromoisobutyl bromide to form macroinitiator HPG-Br. Finally, a hyperbranched star polymer (HPG-PPEGMA) was successfully prepared by atom transfer radical polymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate using HPG-Br as macroinitiator. The structures and properties of the obtained polymers were characterized by ¹H NMR, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The ionic conductivity of the polymer electrolytes composed of HPG-PPEGMA and lithium bis(trifluoromethanesulfonimide) (LiTFSI) was investigated via electrochemical impedance spectroscopy. The results showed that the room temperature ionic conductivity of the prepared hyperbranched star polymer electrolytes had a higher ionic conductivity. When [EO]/[Li] was 20, the ionic conductivity of the hyperbranched star polymer electrolyte was up to 1?×?10^?4 Scm^?1 at 30 °C. The onset decomposition temperature of the hyperbranched star polyether could reach 374 °C, indicating that the hyperbranched star polymer had a good thermal stability. The XRD results showed that the structure of the hyperbranched star polymer was beneficial to improve the ionic conductivity due to possessing a low degree of crystallinity.     

Arm retraction potential of branched polymers in the absence of dynamic dilution

We study the stress relaxation of model polymer networks containing low contents of star shaped and linear dangling polymers. As compared with their melts, the behavior of star and dangling polymers leads to a dynamic response with unprecedented large relaxation times. By comparing data of star melts with those corresponding to stars and dangling chains residing in polymer networks, we were able to identify the effects of dynamic dilution clearly. Since in polymer networks the dynamic dilution effect is suppressed, we were able by the first time to experimentally test the validity of the potential for arm retraction proposed by Pearson and Helfand.     

Hydrodynamic screening of star polymers in shear flow

The mutual effects of the conformations of a star polymer in simple shear flow and the deformation of the solvent flow field are investigated by a hybrid mesoscale simulation technique. We characterize the flow field near the star polymer as a function of its functionality (arm number) f . A strong screening of the imposed flow is found inside the star polymer, which increases with increasing f . To elucidate the importance of hydrodynamic screening, we compare results for hydrodynamic and random solvents. The dependence of the polymer orientation angle on the Weissenberg number shows a power law behavior with super-universal exponent --independent of hydrodynamic and excluded-volume interactions. In contrast, the polymer rotation frequency changes qualitatively when hydrodynamic interactions are switched on.     

Collapse of telechelic star polymers to watermelon structures

Conformational properties of star-shaped polymer aggregates that carry attractive end groups, called telechelic star polymers, are investigated by simulation and analytical variational theory. We focus on the case of low telechelic star polymer functionalities, f < or = 5, a condition which allows aggregation of all attractive monomers on one site. We establish the functionality- and polymerization-number dependence of the transition temperature from the "star burst" to the "watermelon" macroparticle structure. Extensions to telechelic stars featuring partially collapsed configurations are also discussed.     

Preparation and ionic conductivity of composite polymer electrolytes based on hyperbranched star polymer

Hyperbranched star polymer HBPS-(PPEGMA) _x was synthesized by atom transfer radical polymerization (ATRP) using hyperbranched polystyrene (HBPS) as macroinitiator and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as monomer. The structure of the prepared hyperbranched star polymer was characterized by ¹H NMR, ATR-FTIR, and GPC. Polymer electrolytes based on HBPS-(PPEGMA) _x , lithium salt, and/or nano-TiO₂ were prepared. The influences of lithium salt concentration and type, nano-TiO₂ content, and size on ionic conductivity of the obtained polymer electrolytes were investigated. The results showed that the low crystallinity of the prepared polymer electrolyte was caused by the interaction between lithium salt and polymer. The addition of TiO₂ into HBPS-(PPEGMA) _x /LiTFSI improved the ionic conductivity at low temperature. The prepared composite polymer electrolyte showed the highest ionic conductivity of 9?×?10^?5 S cm^?1 at 30 °C when the content of TiO₂ was 15 wt% and the size of TiO₂ was 20 nm.     

Structural transition of nanogel star polymers with pH by controlling PEGMA interactions with acid or base copolymers

We use small angle X-ray scattering (SAXS) to characterise a class of star diblock polymers with a nanogel core on which the outer block arms are comprised of random copolymers of temperature sensitive PEGMA with pH sensitive basic (PDMAEMA) and acidic (PMAA) monomers. The acquired SAXS data show that many of the nanogel star polymers undergo a sharp structural transition over a narrow range of pH, but with unexpectedly large shifts in the apparent pKa with respect to that of the acidic or basic monomer unit, the linear polymer form or even an alternate star polymer with a tightly cross-linked core chemistry. We have demonstrated a distinct and quantifiable structural response for the nanogel star copolymers by altering the core or by pairing the monomers PDMAEMA–PEGMA and PMAA–PEGMA to achieve structural transitions that have typically been observed in stars through changes in arm length and number.     

The Great Myths of Polymer Melt Rheology,Part I: Comparison of Experiment and Current Theory

Abstract

Star polymers consisting of poly(?‐caprolactone), (PCL), grafted onto third generation dendrimer, which had hyperbranched and dendron cores, were studied by polarized light microscopy together with reference linear PCL. The degree of polymerization of the PCL arms in the star polymers ranged between 14 and 81. The star polymers exhibited a greater tendency than the linear polymers to form spherulites. It is suggested that the preference of the star polymers for forming spherulites is due to the presence of amorphous material—dendritic cores and PCL cilia—between crystal lamellae that generates the necessary pressure to force the lamellae to diverge at lamellar branch points. The linear growth rate data followed a single crystallization regime. The fold surface free energy was higher for the star polymers than for their linear analogs. It is proposed that the presence of the large and rigid dendritic cores on the fold surfaces of the star polymer crystals increases the fold surface energy.     

PNIPAM线性链与凝胶在二元溶剂中相变的变温NMR研究

通过对聚N-异丙基丙烯酰胺（PNIPAM）水溶液和凝胶在水和甲醇混合溶剂中的¹H NMR谱图以及弛豫时间(T₁与T₂)等多种NMR参数随温度变化的研究,发现PNIPAM大分子的基团质子NMR信号、溶剂的弛豫时间都可以用来灵敏表征PNIPAM在二元溶剂中的相变行为. 在PNIPAM凝胶中,温度升到LSCT以上,溶剂峰由单峰变为双峰,分别对应于受限在大分子网络内的受限溶剂和排除到大分子网络外的自由溶剂,两者的弛豫时间存在明显差异. 在PNIPAM溶液中,溶剂峰在相变前后并没有显著变化. 通过PNIPAM溶胀在water/alcohol混合溶剂中的相变研究进一步证实了PNIPAM与不同溶剂之间的相互作用强弱.      

Triplet interactions in star polymer solutions

We analyze the effective triplet interactions between the centers of star polymers in a good solvent. Using an analytical short-distance expansion inspired by scaling theory, we deduce that the triplet part of the three-star force is attractive but only 11% of the pairwise part even for a close approach of three star polymers. We have also performed extensive computer simulations for different arm numbers f to extract the effective triplet force. The simulation data show good correspondence with the theoretical predictions. Our results justify the effective pair potential picture even beyond the star polymer overlap concentration. Received 1 September 1999 and Received in final form 18 January 2000