二次纳流电喷雾电离耦合超高分辨质谱检测人体呼出气中相对高分子量化合物

二次电喷雾电离源耦合超高分辨质谱(SESI-UHRMS)有望检出人体呼出气中分子量大于300的相对高分子量化合物,这些化合物的发现将有助于更准确地理解呼出气中挥发性有机化合物(VOCs)的来源、产生机制以及SESI源电离机理,更好地实现SESI-UHRMS的转化应用.本研究自组装nanoSESI源(尚无商业产品)耦合四极杆-静电场轨道阱质谱(最高质量分辨率1.2×10~5),考察了该装置对健康人体呼出气中分子量为300~500化合物的检出情况.结果表明,所搭建的nanoSESI-UHRMS装置检测人体呼出气的重现性好、灵敏度高,可检出数十种分子量为300~500的化合物.根据这些化合物在单次呼气过程中信号强度随时间变化的趋势,推断其来源分别为内源性和外源性;各化合物的元素组成主要包括C,H,N和O,环-双键当量(RDB)的均值为(4.5±3.1),表明检出的化合物可能为醛酮或不饱和脂肪酸,容易在SESI源中被电离.本研究初步验证了自组建nanoSESI-UHRMS检测人体呼出气中相对高分子量化合物的可行性,为后续进一步开展方法应用奠定了基础.     

超高效凝胶色谱法测定聚乙二醇衍生物的分子量及其分布

采用超高效聚合物色谱(APC)技术,以单甲氧基聚乙二醇丙醛(m PEG_p ALD)为代表,测定了聚乙二醇衍生物的相对分子质量及其分布和杂质含量,优选了色谱柱和流动相,考察了样品质量浓度变化以及溶解时间等对测定结果的影响。优化后3根超高效凝胶色谱柱串联,在柱温40℃,流动相95%甲醇,流速0.5m L/min,示差折光检测条件下,对m PEG_p ALD的分子量及其分布进行测定,同时得到杂质的相对含量。结果测得m PEG_p ALD主成分的重均分子量(Mw)为19 444,分布指数(D)为1.01;杂质1的Mw为38 703,D为1.01,含量为1.31%;杂质2的Mw为61 036,D为1.00,含量为0.70%。与常规凝胶渗透色谱(GPC)相比,该方法分辨率高,分析速度快,能快速测定m PEG_p ALD的相对分子量及其分布,并能得到其纯度和杂质含量,为其工艺研发、质量控制提供了科学的依据,同时也可用于其它PEG衍生物的相对分子量及其分布和纯度的测定。     

Atomistic chemical computation of Olefin polymerization reaction catalyzed by (pyridylamido)hafnium(IV) complex: Application of Red Moon simulation

We have realized the microscopic simulation of olefin polymerization, that is, the simulation of the catalytic polymerization (CP) reaction system composed of (pyridylamido)hafnium(IV) complex as the catalyst. For this purpose, we adopted Red Moon (RM) method, a novel molecular simulation method to simulate the complex reaction system. First, according to the previous research, with the help of the QM calculation, we proposed a model system and elementary processes and explained the theoretical treatment of the simulation by the RM method (the RM simulation). In addition, we also proposed a macroscopic simulation based on chemical kinetics simulation. Then, we performed two simulations and compared them in terms of the effective time evolution of the three macroscopic physical quantities, the number-average molecular weight M_n , the mass-average molecular weight M_w , and the molar-mass dispersity Đ_M . The comparison showed that the two simulations are in quantitative or partially qualitative agreement with each other. Therefore, it is concluded that the RM simulation could not only simulate the CP reaction process microscopically, but also it is connected essentially to reproduce the time evolution of the macroscopic physical quantities on the basis of its microscopic simulation data. © 2018 Wiley Periodicals, Inc.     

MEASUREMENT OF NUMBER AVERAGE MOLECULAR WEIGHT OF STYRENE OLIGOMER BY 13C-NMR METHOD

~(13)C-NMR ~1H-decoupled spectra of styrene polymers were assigned by comparison with modelcompounds, then used in measurements of number average molecular weights. The higher limit of an exactdetermination of the end group signal is less than a molecular weight of 10~4. For polymer samples withM_n<10~3, the results obtained from ~(13)C-NMR spectra of saturated carbon region are in excellent agreementwith the values determined by ~1H-NMR, SEC, and VPO methods, while the results from ~(13)C-NMR spectra ofphenyl C-1 carbon region are somewhat higher than the values determined by other methods.     

The effect of the counterion composition on the chain restriction in the cationic polymerization of isobutylene

The effects of the nature of halogens in the initiatingtert-butyl halide-aluminum-containing Lewis acid system on the number average molecular weightM _n and the structure of end groups of polyisobutylene macromolecules obtained in the cationic polymerization of isobutylene in hexane at -78 °C were studied. An increase inM _n is observed in the transition from chlorine to bromine and iodine, accompanied by a decrease in the fraction of end C=C groups and an increase in the relative content of C-Hal groups (Hal = Cl, Br, and I). When atoms of different halogens are present in the counterion, more bulky atoms preferentially participate in the formation of the end groups. The results are interpreted within the framework of the principle of hard and soft acids and bases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1184–1187, May, 1996.     

聚合物连续分级

本文较系统地介绍了聚合物连续分级的理论基础、实验室装置及其实际应用。     

Gel permeation chromatographic characterization of sodium hyaluronate and its fractions prepared by ultrasonic degradation

Summary High-molecular-weight sodium hyaluronate isolated from rooster combs was degraded by ultrasonication. The molecular weight of hyaluronate and its polydispersity was determined by gel-permeation chromatography. During 75-min treatment the molecular weight value decreased from 1.39×10⁶ Da to 2.25×10⁵ Da while the polydispersity of the molecular weight increased from 1.29 to 2.36. The reciprocal value of the square of the hyaluronate's molecular weight was linearly proportional to the time of ultrasonication.     

EFFECT OF MOLECULAR WEIGHT OF PDMS ON MORPHOLOGY AND MECHANICAL PROPERTIES OF PP/PDMS BLENDS

 A series of polydimethylsiloxane (PDMS) with varied molecular weights (Mw = 3 &#61620; 106, 1 &#61620; 106 and 0.5 &#61620; 106) were melt blended with PP to investigate the effect of PDMS molecular weight (MW) on the morphology and mechanical properties of PP/PDMS blends. Scanning electron microscopic (SEM) examination showed that the size of PDMS domains was dependent on the MW of PDMS. It was found that the lower the value of PDMS MW, the better dispersion of the PDMS domains in the PP matrix. Tensile and Izod impact tests revealed that the addition of PDMS with lower MW would lead to a more significant increase in impact strength of the blends compared with the blends with higher MW ones, while the influence of the molecular weight on tensile strengths of the blends was relatively small in the MW range studied. Differential scanning calorimetry (DSC) results also showed that the crystallization temperature of PP was increased with decreasing PDMS MW, indicating a better nucleation capability of lower MW of PDMS. Melting flow rate (MFR) measurements indicated that the processibility of PP could be enhanced by adding PDMS, and again the lower MW PDMS resulted in better data. Our work demonstrates that not only the processibility but also the mechanical properties of PP could be enhanced to a more significant degree by using low MW PDMS than the higher ones.     

Synthesis of tailor‐made polyethylene through the control of polymerization conditions using selectively combined metallocene catalysts in a supported system

Tailoring of the molecular weight distribution (MWD) in ethylene polymerization was attempted by selectively combining different types of metallocene catalysts onto a single support. The catalyst produced by supporting Et[Ind]₂ZrCl₂ and Cp₂HfCl₂ onto a single MAO pretreated silica support was able to produce polymers with unimodal or bimodal MWD's. This approach permits the synthesis of polyethylene with different MWD's using the same catalyst as a function of the polymerization conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 331–339, 1999     

Degradation and stabilization of polycyanoacrylates

Polycyanoacrylates were found to be inherently unstable. Even in the absence of a deliberately added strong base, their molecular weights decreased drastically on standing in solution in accord with observations by Ryan and McCann (Makromol Chem Rapid Commun 1996, 17, 217). The initial high molecular weight polymer disappeared over the course of a few hours in solution and was replaced by a much lower molecular weight material. For polymers made by anionic polymerization, the entire sample degraded, but for polymers made by free-radical polymerization, only a portion of the sample was affected. This behavior was consistent with the mechanism proposed by Ryan and McCann, in which the polymer chains are in dynamic equilibrium with their monomers and the polymer degrades from its chain terminus. Surprisingly, the degradation in molecular weight even occurred slowly in the solid state. The degradation was inhibited by acids and could be prevented by free-radical copolymerization with small amounts of more stable monomers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4570–4581, 1999