一种用高效凝胶渗透色谱测试褐藻胶分子量及分子量分布的方法

提出了一种用凝胶色谱与常规检测器检测褐藻胶分子量及其分布的方法。用高效凝胶渗透色谱(GPC)与示差检测器(RID)结合，建立了以普鲁兰标准品为对照的相对重均分子量、相对数均分子量与GPC–MALLS(多角度激光散射)测试的褐藻胶绝对重均分子量、绝对数均分子量间的转换关系，得到了用GPC–RID检测相对分子量计算褐藻胶绝对分子量和多分散系数的方法。结果表明，GPC–RID法经转换公式得到的重均分子量、数均分子量和多分散系数与GPC–MALLS法的相对误差在?12%以内。基于GPC–RID法可较准确地获得褐藻胶的绝对分子量及多分散系数，使用通用检测器可节约仪器投资，降低检测成本。     

Reliability of molecular weight determination methods for oligomers investigated using certified polystyrene reference materials

Using polystyrene certified reference materials (CRMs) whose molecular weights range from 500 to 2400, we investigated the reliability of molecular weight determination by size-exclusion chromatography (SEC), SEC coupled with multi-angle light scattering detection (SEC-MALS), conventional static light scattering (SLS), matrix-assisted laser desorption/inonization time-of-flight mass spectrometry (MALDI-TOFMS), and ¹H NMR. Average molecular weights determined by these methods were compared with the certified values which were determined by supercritical fluids chromatography with relative standard uncertainty less than 1%. The comparison showed that recent SEC with calibration constructed by uniform polystyrenes can provide just the same average molecular weights as certified ones within the standard uncertainty. ¹H NMR was also found to be a powerful technique to determine number-average molecular weight accurately. Average molecular weights measured by SEC-MALS and SLS nearly agreed with certified values except for lower molecular weights. Although MALDI-TOFMS provided average molecular weights in agreement with certified values, the polydispersity given by MALDI-TOFMS were found to be very small for all the polystyrenes.     

Gel permeation chromatography of polyethylene. I. Calibration

An accurate GPC calibration is essential if computer techniques are to be utilized in obtaining the molecular weight distribution and degree of long-chain branching from an intrinsic viscosity and GPC trace of a polymer. The use of the National Bureau of Standards Linear Polyethylene Standard Reference Material, SRM 1475, to calibrate GPC is described. Employing this calibration, the Mark–Houwink relationship for linear polyethylene in 1,2,4-trichlorobenzene was established utilizing narrow molecular weight fractions derived through fractionation of SRM 1475 and other polymers. This Mark–Houwink equation was subsequently employed for the evaluation of high molecular weight fractions which were then used to extend the GPC calibration to the high molecular weight region not covered by SRM 1475. An iterative technique was used to obtain coincidence of the measured intrinsic viscosity and the viscosity calculated from the GPC data. The accuracy of the GPC calibration was demonstrated by obtaining coincidence of the measured and calculated viscosity of high and low molecular weight polymers of both narrow and broad polydispersity.     

Gel permeation chromatography of the xanthan gum using a light scattering detector

Summary This work gives the first gel permeation chromatogramms obtained on native xanthan using a refractometric and a light scattering detectors. Results of molecular weights distribution analysis give a polydispersity 1.2 for the native polymer and 1.7 for enzymic partially degraded polymer. The experimental conditions and chromatogramms interpretation are briefly discussed.Laboratoire Propre de C.N.R.S., associé à l'Université Scientifique et Médicale de Grenoble     

ABA block copolymers without tapering by isokinetic living anionic polymerization in a series of stirred tank reactors

Equations for the molecular weight distribution and the average molecular weights of a living anionic polymerization with very rapid or slow initiation are presented for a series of stirred tank reactors. It is shown that polydispersity of the polymer in the last vessel of a cascade takes for nearly complete conversion of monomer then a minimum, when the reaction is performed isokinetically with concern to monomer conversion, i.e. when monomer conversion in each vessel of a cascade of n tanks is 1/n. Now, polydispersity of the polymer in the mth vessel of the cascade (1 ≤ m ≤ n) is D_m = 1 + 1/m. Values of all systems variables needed for isokinetic control of the polymerization may be precalculated from kinetic models. For vessels of equal size and with equal residence times reaction temperature is suggested as control variable increasing stepwise from vessel to vessel. The proposed procedure was checked for the systems styrene/n-butyllithium/toluene, styrene/s-butyllithium/benzene, and isoprene/s-butyllithium/n-heptane. A satisfying agreement between calculated and measured values of the objectives monomers conversion, number average molecular weight, and polydispersity was found. It is proposed to use the described procedure for the preparation of ABA block copolymers with negligible tapering between the blocks by living anionic polymerization in a series of stirred tank reactors.     

The molecular weight average obtained by combining quasielastic light-scattering and intrinsic viscosity measurements

For “monodisperse”, randomly coiled macromolecules, we find that the molecular weight, intrinsic viscosity, and diffusion coefficient are accurately related by This equation holds for denatured proteins in 6M GuHCl(aq) as well as for narrow polystyrene fractions in tetrahydrofuran. For a Schulz distribution of molecular weights, the weight measured from combining diffusion and viscosity data is closely approximated by These equations are verified with measurements of wide molecular distributions of polystyrene in toluene and data from the literature. These relations provide a rapid, nondestructive method to determine a well-specified molecular weight average of small quantities of polymers in a wide diversity of solvents using quasielastic light scattering techniques to evaluate polymer diffusion coefficients.     

Calibration of thermal field-flow fractionation using broad molecular weight standards

Thermal field-flow fractionation (ThFFF) is a new elution-based separation method for determining molecular weight distributions of polymers. Calibration can be achieved using monodisperse standards of the specific polymer of interest. In order to expand the range of polymer types for which absolute molecular weight data can be obtained using ThFFF a calibration procedure has been developed and tested which uses only broad molecular weight polymer samples. The method requires two polydisperse molecular weight standards of the required polymer whose average molecular weight (normally M?_w) is measured by an independent method (e.g. light scattering). From the average molecular weight data and the ThFFF elution pattern (fractogram) the required calibration constants can be calculated. The method has been tested using the polystyrene-tetrahydrofuran system and gave satisfactory results when checked against a series of monodisperse polystyrene standards. This calibration approach should expand the applicability of ThFFF to include a wide range of polymer types.     

Structure of colloidal particles in water-oil mixtures stabilized by polymeric emulsifiers. 3. Hydrodynamic properties

The micellar properties of water-oil mixtures stabilized by polystyrene-poly(ethyleneoxide) graft copolymers, in the presence of an alcohol, have been investigated by quasielastic scattering of laser light and viscometry. The mean size, aggregation number, polydispersity and swelling degree of the polymeric micelles have been deduced for a series of copolymers as a function of the solvent composition. Both size and aggregation number are strongly dependent on the toluene/water ratio. The swelling degree of particles is primarily controlled by the weight ratio polystyrene/poly(ethyleneoxide).     

Spherulite crystallization in bisphenol-A-polycarbonate of varying molecular weight distribution

The spherulitic structure of films of fractionated bisphenol-A-polycarbonate having a range of different average molecular weight and molecular weight distribution has been studied using the polarization microscope. Spherulitic crystallization was induced in specimens by the action of solvent or solvent vapor at room temperature or by isothermal heat treatment at 180°C. These phenomena were all shown to be a function of the average molecular weight and polydispersity of the material. The glassy amorphous and spherulite polymer phases were investigated using a microscopic etching technique and gel permeation chromatography (GPC). Results of this investigation have established that considerable segregation by molecular weight occurs during the crystallization process. Spherulites produced have been shown to exhibit variation in morphologic texture depending on conditions of induction and polydispersity of the polymer. Examples of unusual and previously unreported spherulites have been observed.     

Superparamagnetic latex synthesized by a new route of emulsifier‐free emulsion polymerization

The aim of this study was to design polymeric nanospheres containing magnetic nanoparticle which could display superparamagnetic behavior and thus find application in allied fields. First magnetite nanoparticles were synthesized with coprecipitation method and then their stable acidic dispersion was prepared without surfactant and dropped into the polymerization system during a certain time interval after the polymerization started. The effects of time at which the magnetic sol was added into polymerization system on latex size and stability, average molecular weight of polymer were examined in the case of two different monomer concentrations. Extensive characterization by transmission electron microscopy, dynamic light scattering, thermal gravimetric analysis and magnetic measurements shows that when the magnetic sol was dropped during earlier time of polymerization at stage 1, the latex size, average molecular weight of polymer, thermal stability of polymeric composite, and saturation magnetization reduced, whereas polydispersity of size and molecular weight increased because of the reaction between persulfate and naked surface of magnetite at the aqueous phase. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Gel permeation chromatography: Dispersion effects on molecular weight monitor-installed gel permeation chromatograph

Computer simulation was carried out to examine the performance of a molecular weight (MW) monitor-installed gel permeation chromatograph (GPC), by taking account of the effects of limited column resolution according to Tung's phenomenological scheme. Efficiency of GPC fractionation was discussed also in the same light. For simulated GPC fractionation results of model polymers having log-normal distribution, various average MW's and MWD functions were calculated from the data obtained by the MW monitor method as well as the conventional MW calibration methods, and compared with the given true values. The MW monitor method generally tends to predict narrower distributions than the true ones, as opposed to the conventional calibration methods which usually predict broader distributions. For certain simple cases, semiquantitative relation between the extent of column resolution and these deduced average MW's was derived. The efficiency of GPC fractionation (as judged, for example, by the polydispersity of recovered fractions) is limited by such factors as fraction size, column resolution, and polydispersity of the original sample itself.     

Evolution to similarity solutions for polymerization and depolymerization with microwave radiation

The kinetics of polymerization and depolymerization are critical in understanding the stability and characterization of polymers. The kinetics of simultaneous polymerization and degradation of poly(methyl methacrylate) have been investigated by varying the initiator concentration and monomer concentration under the influence of microwave energy. Microwave radiation initially polymerizes the monomer, then degrades the resulting polymer and the polymer attains an equilibrium molecular weight distribution with a polydispersity of two. To understand more fully the kinetics, the molecular weight distribution (MWD) is represented as a gamma distribution; the random degradation rate coefficient is assumed to vary linearly with molecular weight and the polymerization rate coefficient is assumed to be independent of molecular weight. The change of the MWD with time is studied by continuous distribution kinetics; the solutions obtained depict the change of the average molecular weight, polydispersity and the gamma distribution parameters with time. Experimental data indicate that reaction rates are enhanced by microwave radiation and the MWD approaches a similarity solution within 10 min for all the investigated cases. The model satisfactorily predicts the change of the MWD with time. © 2001 Society of Chemical Industry     

The influence of impingement mixing on striation thickness distribution and properties in fast polyurethane polymerization

Impingement mixing in a polyether polyol/butanediol/MDI, thermoplastic urethane system was evaluated using measurements of striation thickness distribution, adiabatic temperature rise, and molecular weight. Adiabatic temperature rise was less sensitive to mixing quality for this system than for the crosslinking ones previously studied. The average of the distribution of striation thickness as measured by optical microscopy on the resultant polymer decreased with increasing nozzle Reynolds numbers, Re. Molecular weight increased and its polydispersity decreased with increasing Re. Morphological data indicate better phase separation in the poorly mixed samples. These results are consistent with relatively slow diffusion for the polyol and thus the preferential formation of unattached hard segments at lower Re.     

Molecular weight distribution of commercial PVC

The molecular weight distribution (MWD) of commercial suspension grade poly(vinyl chloride) (PVC) resins with K values from 50 to 93 and mass grade PVC resins with K values from 58 to 68 has been determined by size exclusion chromatography (SEC), using literature Mark‐Houwink coefficients. The MWD is characterized by the number average molecular weight (M_n), the weight average molecular weight (M_w) and the polydispersity (M_w/M_n). Our results for M_w are consistent with recently published data, but we find different results for M_n and consequently for M_w/M_n. The polydispersity of PVC increases with increasing K value. This effect can be explained by two mechanisms. The first mechanism is a reduced terminating reaction rate between two growing polymer chains (disproportionation) at higher molecular weight owing to the reduced mobility of the polymer chains. The second mechanism is long‐chain branching of molecules with high molecular weight which lets the molecules grow at two ends. For two examples graphs of the measured MWD are compared with the theoretically expected MWD.     

Molecular weights of solubilized lignite macromolecules

The determination of molecular weights and molecular weight distributions in humic acids derived from lignite by base extraction has been successfully carried out by low-angle laser light scattering (LALLS) photometry and by coupling size exclusion chromatography (SEC) with LALLS photometry. Since light scattering techniques give absolute molecular weight values, no error-prone calibrations of the size exclusion column were necessary. Reduction of soluble derivatives of the humic acids with zinc in acetic anhydride was required to reduce the optical absorbance so that a linear scattering response was observable. Weight average molecular weights of ≈ 1.3 × 10⁶ and low polydispersity ratios were obtained for humic acid derivatives of Beulah, ND, lignite. Extension of this technique to the study of the more highly crosslinked humin which comprises the major portion of the lignite was investigated by treatment of the lignite with sodium hydroxide solution in a blender. This treatment converted up to 90% of the lignite into humic acids, which could be derivatized and studied by the LALLS techniques. The molecular weights of the products from lowtemperature solubilization of the lignite are inversely proportional to the per cent conversion.     

Propene polymerization with MgCl2-supported TiCl4/dioctylphthalate catalyst. III. Effects of polymerization conditions on molecular weights and molecular weight distribution

In propene polymerization over the MgCl₂-supported TiCl₄/dioctylphthalate (DOP) catalyst, the weight- and number-average molecular weights and the molecular weight distribution (MWD) of polypropene products and of the isotactic and atactic polymer portions were studied. The average molecular weights and MWD were found to be independent of time. The isotactic polymer had higher molecular weight and broader distribution than the atactic portion by almost an order of magnitude. An increase in temperature and cocatalyst/catalyst ratio resulted in lowering molecular weight due to increasing transfer reaction. Alkyl aluminum was used as a cocatalyst, and the molecular weight did not vary significantly with different alkyl groups. Of the three external bases studied, 2,2,6,6-tetramethyl piperidine (TMPIP), dimethoxydiphenyl silane (DMDPS), and t-butylmethyl ether (TBME), the addition of a small amount of one of the first two bases caused a substantial increase in both molecular weight and polydispersity of the isotactic polymer. Those increases leveled off quickly with increasing amounts of the external base. On the other hand, both average molecular weights and polydispersity of the atactic polymer decreased with a net increase in the molecular weight of the whole polymer. TBME, however, has no significant effect on either molecular weight or MWD. These effects are discussed in the context of the roles of the external base in propene polymerization. © 1995 John Wiley & Sons, Inc.     

Stochastic model for living radical polymerisation of styrene initiated by epoxide radical ring opening

A stochastic model was developed to simulate the polymerisation kinetics and the detailed microstructure of the resulting polymers made by the living radical polymerisation of styrene initiated by epoxide radical ring opening. The model was used to predict monomer conversion, average molecular weight, polydispersity index, and molecular weight distribution as a function of polymerisation time. Simulations were used to explore the effects of rate constant values on chain microstructures and polymer properties and validated with experimental data published in the literature. It was found that some parameters, such as the exchange rate constant, have no significant effect on the polymerisation kinetics, whereas major effects were observed when other rate constants, such as the reduction rate constant, were changed.     

On-Line Coupling of Thermal Field-Flow Fractionation with Low-Angle Laser Light Scattering

Abstract

The analysis of a polymethyl methacrylate sample dissolved in dimethylformamide is performed by using a low-angle laser light scattering photometer attached to a thermal field-flow fractionation channel and a differential refractometer. Relevant theoretical light scattering equations for flow-through operation are outlined. It is shown that the calibration curve of the separation system can be constructed in situ during the course of separation, without using any calibration standard. The average molecular weights as well as the molecular weight distribution curves of the polymer have been determined. The sensitivity of the light-scattering photometer has been measured, and it is compared to that of the differential refractometer in terms of signal-to-noise ratios. The various sources of errors in the molecular weight determination are discussed, and the potential of the coupling for physicochemical studies on the thermal diffusion of polymers is indicated. In spite of some inherent problems, this coupling is expected to have a very bright future if reliable low-angle light-scattering instruments can be made available at moderate prices.     

驱油用水解聚丙烯酰胺分子量测定方法研究进展

聚合物分子量及分子量分布是水解聚丙烯酰胺评价和合成研究的重要指标之一,在研究其黏度、水力学半径、降解规律和聚合物筛选评价等方面有着重要应用。本文简要回顾了黏度法、光散射法、凝胶色谱法、联用技术、场流技术的基本原理及在测定水解聚丙烯酰胺分子量中的应用及发展情况。黏度法设备简单,对操作人员要求较低,易于掌握,是目前主要评价手段;光散射法对样品除尘等要求较高,主要用于机理研究与分析,在大庆油田已有应用;驱油用的水解聚丙烯酰胺由于分子量大、非体积效应显著,应用凝胶色谱技术测其分子量还需要做大量的研究工作;场流技术能有效解决聚合物分子的剪切断裂问题,具有比较广阔的发展前景。     

Prediction of Flory–Huggins interaction parameters from intrinsic viscosities

Previous articles from this laboratory have described a model for predicting the second virial coefficient of a polymer solution given the polymer molecular weight and its intrinsic viscosity in the particular solvent. The same theory is used in this report to calculate values of the Flory–Huggins interaction parameter χ. The method is different in that χ is obtained through manipulation of simulated exprimental data in exactly the same way as in an actual experiment. Agreement between estimated χ values and those obtained at infinite dilutions from membrane osmometry or light scattering is within 2%, on the average. The model accounts for the molecular weight dependence of χ.