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1.
Abstract Using the theories of random degradation of Montroll and Simha, relationships are derived among limiting viscosity number, degree of degradation, and number-average molecular weight for a polymer undergoing random degradation in a closed system. Relationships among these parameters are derived for initial distributions of the “coupling” and the monodisperse types. Computer programs have been written which rapidly provide reliable values of number-average molecular weights and degrees of degradation from measured viscosity data on polymers with these initial distributions undergoing random degradation. 相似文献
2.
从GPC和特性粘数计算高聚物各种平均相对分子质量的新方法 总被引:7,自引:0,他引:7
聚合物相对分子质量表征问题可以从GPC数据和特性粘数较可靠地迅速解决,同时求出其烽均、粘均、重均,动力学平均相对分子质量及相对分子质量-特性粘数关联参数。为些须对以往方法作较大的改进,其关键是用迭代法进行特性粘数与相对分子质量的关联。方法经用聚甲基丙烯酸甲酯验证后用于聚碳酸亚乙酯(PEC)和聚碳酸亚丙酯(PPC)分别得到关系式。 相似文献
3.
香菇多糖的成分及其分子量研究 总被引:29,自引:2,他引:29
从香菇子实体中用0.9%NaCl水溶液、85%乙醇、热水、1%草酸铵、5%NaOH/0.05%NaBH4和2%NaOH/2%尿素分别提取出四种杂多糖(L-FⅠ-L-FⅣn)和两种葡聚糖(L-FⅤ和L-FⅥn).红外光谱和高效液相色谱分析结果表明杂多糖主要由葡萄糖、葡萄糖醛酸、木糖、甘露糖、半乳糖和鼠李糖组成,而且按照分离过程的进行多糖中葡萄糖含量递增.由光散射和膜渗透压法研究了多糖的重均分子量Mw、均方根旋转半径2>1/2、第二维利系数A2及数均分子量Mn.L-FⅡ、L-FⅢ、L-FⅤ及L-FⅥn的Mw值依次为19.7×104、192.3×104、136.4×104和136.7×104,它们的多分散系数-Mw/-Mn在3~5范围. 相似文献
4.
《液相色谱法及相关技术杂志》2012,35(3):413-423
Abstract A short program was written for a pocket programmable calculator (HP-29C), to reduce data from a Gel Permeation Chromatogram. The output of this program consists of weight-and number-average molecular weights, polydispersity, and normalized weight distribution. All were uncorrected for dispersion. Mathematical approximation of the GPC calibration curve was made by exponential fit, also performed on the programmable calculator. The program and its application to NBS 706 and one narrow-molecular weight distribution (NMWD) polystyrene standards are presented. With slight modification, the program can be used on newer, more powerful calculators such as the HP-41C, on which dispersion correction subroutines could be performed. 相似文献
5.
Colloid Journal - An empirical expression based on the general notions of available structural and diffusion theories of viscous flows has been proposed for the viscosity coefficients of molecular... 相似文献
6.
本文用唐敖庆的方法研究了Aα-Bb(B′)bCc、Dd型缩聚物的平均分子量。将三种特例的理论曲线和实验结果相比较,两者基本相符。 相似文献
7.
The molecular transfer printing(MTP) technique has been invented to fabricate chemical patterns with high fidelity using homopolymer inks. In this work, we systematically studied the effects of the molecular weights of homopolymer inks and transfer conditions on the MTP process. We explored a large range of molecular weights(~3.5-56 kg·mol~(-1)) of hydroxyl-terminated polystyrene(PS-OH) and hydroxyl-terminated poly(methyl methacrylate)(PMMA-OH) in the MTP process, and found that the resulting chemical patterns on replicas from all five blends were functional and able to direct the assembly of films of the same blends. The transfer temperature and the film annealing sequences had an impact on the MTP process. MTP was sensitive to the transfer temperature and could only be performed within a certain temperature range, i.e. higher than the glass transition temperature(T_g) of copolymers and lower than the rearrangement temperature of the assembled domains. Pre-organization of the blend films was also necessary for MTP since the preferential wetting of PMMA domains at the replica surface might result in the formation of a PMMA wetting layer to prevent the presentation of underlying chemical patterns to the replica surface. 相似文献
8.
A new method for the determination of the sedimentation coefficient-molecular weight relation is proposed. Based on the very low sensitivity of the corresponding sedimentation coefficient average S 0,1 and the weight-average molecular weight M w (calculated according to the generalized Flory-Mandelkern equation) to changes of the a parameter, the S0,1 and M w values are estimated from constant initial values of the as parameter for all those polymer-solvent systems for which the real as values do not exceed the interval 0.3-0.5. The approximations involved give an error lower than 8.5%, Le., below the experimental errors of the Mw values determined for polydiSDerse samDles. The new method of determining the So -M relation was applied to the system styrene-acrylonitrile copolymer (22.6-wt%oacrylonitrile content) in acetone at 25°C and yielded the following relation: S0=2.90 × 10 ?15 M 0,49 sec. Although in the case of this polymer-solvent system the a value of 0.49 is close to the one corresponding to θ systems, the method is shown by model calculations to be of general applicability and especially useful in the case of nonideal polymer-solvent systems. 相似文献
9.
Abstract A new empirical equation is presented which modifies the Krigbaum equation for calculating Kθ values from measurements of intrinsic viscosity in good solvents. This is found to fit the molecular weight data better for the polymer systems investigated. 相似文献
10.
Abstract In this study viscosity measurements of polyadenylic acid (PolyA) in aqueous solution were carried out under different conditions. In the absence of any additives, the polymer degraded during flow through the capillary of a viscometer or when standing still. Degradation during the former was more severe. The degradation of polyadenylic acid can be prevented by addition of an electrolyte such as KCl to increase the ionic strength. However, in this case the deviation from linearity was still considerable at most ionic strength values. The best fit to the Huggins and Kraemer equations was obtained using a Tris–EDTA buffer solution with a final pH of 7.65. Estimation from intrinsic viscosity and weight-average molecular weight values gave k and α as 2.04 × 10?5 and 0.89 from the equation η = kM α. The difference between Huggins (k 1) and Kraemer (k 1′) constants was close to 0.50 for all measurements. 相似文献
11.
C. W. Pyun 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1721-1725
The reason why two generalized logarithmic normal distributions with the same set of two average molecular weights are interconvertible is discussed. The generalized distribution, however, appears in polymer chemistry in a different context. 相似文献
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13.
A relationship between intrinsic viscosity and molecular weight for fractionated cellulose is established. The exponent a of the Mark-Houwink equation is 0.80. The unperturbed dimensions of cellulose are discussed on the basis of the Stockmayer-Fixman and Kurata-Stockmayer viscometric theories, and it is determined that cellulose is not a very rigid macromolecule in nature. This conclusion disagrees with the results obtained by statistical mechanics procedures in which the restriction of β-glucose residues to the C1 conformation was kept. The steric hindrance factor, σ is about 2, and it seems to be independent of the substituents in cellulose if it is evaluated in both cellulose and cellulose derivatives from viscometric data. From statistical mechanics data reported in the literature, σ is estimated as 4.4 for cellulose and cellulose derivatives, such as cellulose nitrate, and this means that the steric hindrances of the substituents have little influence on the rigidity of cellulose derivatives. This view disagrees with the results obtained from the non-Newtonian behavior of cellulose and cellulose nitrate in dilute solutions. By applying the Noda-Hearst theory, the conclusion is reached that cellulose nitrate is a more extended macromolecule than cellulose. 相似文献
14.
Yuriy N. Malyar Natalia Yu. Vasilyeva Aleksandr S. Kazachenko Valentina S. Borovkova Andrei M. Skripnikov Angelina V. Miroshnikova Dmitriy V. Zimonin Vladislav A. Ionin Anna S. Kazachenko Noureddine Issaoui 《Molecules (Basel, Switzerland)》2021,26(17)
The process of sulfation of arabinogalactan—a natural polysaccharide from Larix sibirica Ledeb.—with sulfamic acid in 1,4-dioxane using different activators has been studied for the first time. The dynamics of the molecular weight of sulfated arabinogalactan upon variation in the temperature and time of sulfation of arabinogalactan with sulfamic acid in 1,4-dioxane has been investigated. It has been found that, as the sulfation time increases from 10 to 90 min, the molecular weights of the reaction products grow due to the introduction of sulfate groups without significant destruction of the initial polymer and sulfation products. Sulfation at 95 °C for 20 min yields the products with a higher molecular weight than in the case of sulfation at 85 °C, which is related to an increase in the sulfation rate; however, during the further process occurring under these conditions, sulfation is accompanied by the destruction and the molecular weight of the sulfated polymer decreases. The numerical optimization of arabinogalactan sulfation process has been performed. It has been shown that the optimal parameters for obtaining a product with a high sulfur content are a sulfamic acid amount of 20 mmol per 1 g of arabinogalactan, a process temperature of 85 °C, and a process time of 2.5 h. 相似文献
15.
Valuev V. I. Mikhailova L. N. Okhotnikov M. A. Dal'gren I. V. 《Russian Journal of Applied Chemistry》2004,77(5):835-837
Polycondensation of bifunctional hydroxyl-containing oligodienes with diisocyanates was studied by gel permeation chromatography, IR spectroscopy, and rheokinetic method. The kinetics of oligodiene urethane formation and the properties of the resulting oligomers, including the molecular-weight distribution and viscosity, were studied in relation to the ratio of the isocyanate and hydroxy groups. 相似文献
16.
Atomic Displacement Parameters (ADPs) of anthracene (94 – 295 K), (D10)anthracene (16, 295 K), naphthalene (92 – 239 K), and (D8)naphthalene (12, 295 K) have been analyzed with the help of an Einstein‐type model of local, molecular normal modes. The low‐frequency motions are expressed in terms of molecular translations, librations, and deformations, and account for the temperature dependence of the experimental ADPs. Their frequencies decrease with increasing temperature due to crystal expansion. For anthracene, enough data of sufficient quality are available to determine two low‐frequency out‐of‐plane deformation modes. The corresponding frequencies of naphthalene are much higher and cannot be extracted from the available data, which are more limited qualitatively and quantitatively. The mean‐square amplitudes due to the high‐frequency normal modes are also extracted from the diffraction data. They agree satisfactorily with those obtained for molecules in the gas phase from density‐functional theory. Contributions to the ADPs that cannot be interpreted in terms of motion are small but significant. The case study presented here shows that dynamic aspects of molecular structure can be obtained from single‐crystal diffraction studies. For optimal results, experiments must be performed over as large a temperature and resolution range as possible, and factors affecting ADP's but not representing motion have to be kept to a minimum, e.g., by avoiding disorder, parametrizing X‐ray data with multipole models, and minimizing absorption and extinction. 相似文献
17.
Antibacterial polymers of dimethylaminoethyl methacrylate benzyl ammonium chloride(DMAEMA-BC) with various molecular weights(Mws) were prepared under controlling radical polymerization conditions. The Mws of these polymers were determined by means of static multiangle laser light scattering and viscosity method. A Mark-Houwink equation was established to be [η]=0.154M0.764 for the Mw evaluation of poly(DMAEMA-BC)s. The effects of the Mws of these poly(DMAEMA-BC)s on their antibacterial activities against E. coli and S. aureus were investigated by various methods including viable cell counting, electrical conductivity titration, intracellular constituent leakage tests and electron microscopy. Our results indicate that the antibacterial efficiency of DMAEMA-BC was significantly enhanced after the monomers were polymerized into a polymer and increased obviously with the Mws,as a result of the increase of charge density. Further investigation of the molecular basis underlying the anti-bacterial role of these polymers revealed that poly(DMAEMA-BC) promoted the release of potassium ion from the membrane of bacterial cells and the release increased significantly with the Mws of the polymers used. 相似文献
18.
Qian Li Yuehu Li Zehua Jin Yujie Li Yifan Chen Jinping Zhou 《Molecules (Basel, Switzerland)》2021,26(11)
Water-soluble cellulose ethers are widely used as stabilizers, thickeners, and viscosity modifiers in many industries. Understanding rheological behavior of the polymers is of great significance to the effective control of their applications. In this work, a series of cyanoethylcellulose (CEC) samples with different molecular weights were prepared with cellulose and acrylonitrile in NaOH/urea aqueous solution under the homogeneous reaction. The rheological properties of water-soluble CECs as a function of concentration and molecular weight were investigated using shear viscosity and dynamic rheological measurements. Viscoelastic behaviors have been successfully described by the Carreau model, the Ostwald-de-Waele equation, and the Cox–Merz rule. The entanglement concentrations were determined to be 0.6, 0.85, and 1.5 wt% for CEC-11, CEC-7, and CEC-3, respectively. All of the solutions exhibited viscous behavior rather than a clear sol-gel transition in all tested concentrations. The heterogeneous nature of CEC in an aqueous solution was determined from the Cox–Merz rule due to the coexistence of single chain complexes and aggregates. In addition, the CEC aqueous solutions showed good thermal and time stability, and the transition with temperature was reversible. 相似文献
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20.
G. E. Walrafen W.-H. Yang Y. C. Chu M. S. Hokmabadi 《Journal of solution chemistry》2000,29(10):905-936
Addition of water to stoichiometric 100% sulfuric acid increases the density untila maximum results near 87 mole% H2SO4. The density and conductivity maximaand viscosity minimum, the latter two near 75 mole%, are direct macroscopicresponses to microscopic quantum mechanical properties of H3O+ and of nearlysymmetric H-bond double-well potentials, as follows: (1) lack of H bonding tothe O atom of H3O+; (2) short, 2.4–2.6 A, O—O distances of nearly symmetricH bonds; and, (3) increased mobility of protons in such short H bonds, give riseto the density maximum via (1) and (2); (1) produces the viscosity minimum;and the conductivity maximum results from (2) and (3). A pronounced minimumnear 1030 cm–1 in the symmetric SO3 stretching Raman frequency of HSO4
–,observed near 45 mole% also results from double-well effects involving the shortH bonds of direct hydronium ion—bisulfate ion pair interactions. Estimates of theconcentrations of the (H3O+)(HSO4
–) and (H2SO4)(HSO4
–) pair interactions weredetermined from Raman intensity data and are given for compositions between42–100 mole% 相似文献