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。     

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.     

Molecular weights and molecular weight distributions of irradiated cellulose fibers by gel permeation chromatography

Radiation degradation of cellulose fibers was investigated by gel permeation chromatography (GPC). Scoured cotton of Mexican variety (cellulose I), Polynosic rayon (cellulose II), and their microcrystalline celluloses obtained by hydrolysis of the original fibers were irradiated by Co-60 γ-rays under vacuum or humid conditions. The irradiated samples were then nitrated under nondegradative conditions. The molecular weights and molecular weight distributions were measured by GPC using tetrahydrofran as solvent. The relationship between molecular weight and elution count was obtained with cellulose trinitrate standards fractionated by preparative GPC. The degree of polymerization of the fibers decreased with increasing irradiation dose, but their microcystalline celluloses were only slightly degraded by irradiation, especially in microcrystalline cellulose from cellulose I. Degradation of the fibers irradiated under humid conditions was less than that irradiated under vacuum. It was found that the G-values for main-chain scission for the irradiated cellulose I, cellulose II, microcrystalline cellulose I, and microcrystalline cellulose II were 2.8, 2.9, less than 1, and 2.9, respectively, but the G-value for main-chain scission for the irradiated cellulose II was increased to 11.2 at irradiation doses above 3 Mrad. Consequently, it is inferred that cellulose molecules in the amorphous regions are degraded more readily, and the well-aligned molecules in crystalline regions are not as easily degraded by irradiation.     

Molecular weight characterization of fluoropolyoxyalkylenes by gel permeation chromatography

Conditions required for the molecular weight and molecular weight distribution determination of fluoropolyoxyalkylenes by gel permeation chromatography are reported and discussed. Experimental work was carried out with three series of narrow fractions of oligomers having the same perfluorinated copolymeric body and three different types of chain ends. The same calibration curve describes very well the behavior of the three series of samples, so that a “size-exclusion” mechanism of the molecular separation can be postulated practically. © 1994 John Wiley & Sons, Inc.     

A gel permeation chromatography calibration method for a broad molecular weight distribution polymer

A novel, precise, and simple method is described for developing a GPC calibration curve for a polymer where only broad molecular weight distribution samples are available. The method demands a GPC calibration curve for another polymer (e.g., polystyrene) and measurement of the intrinsic viscosity and an average molecular weight for each of several samples of the broad molecular weight distribution polymer in addition to GPC measurements on those samples. Results of applying the procedure to poly(n-lauryl methacrylate) are presented.     

A new method for calculating and correcting molecular weight distributions from gel permeation chromatography

A new method for calculating and correcting molecular weight distributions of polymer samples from GPC chromatograms is presented. The integral equation which relates the true molecular weight distribution of polymer sample to the chromatogram is reformulated into an equivalent variational problem of quadratic functional. The method of steepest descent in the function space is then applied to the minimization problem to obtain the true molecular weight distribution. This method is efficient and reduces some of the oscillation problems encountered in the previous methods. Examples are given.     

A rapid technique for measuring copolymer composition as a function of molecular weight using gel permeation chromatography and infrared detection

A gel permeation chromatograph using an infrared spectrometer detector is described. Operation in a stop-and-go fashion permits rapid determination of copolymer composition as a function of molecular weight. A broad distribution copolymer, poly(vinyl chloride–co–vinyl stearate), showed marked compositional changes with molecular weight. The changes observed are not in agreement with those predicted from reactivity ratios.     

An analytical correction for peak broadening in gel permeation chromatography with a molecular weight detector

Summary In this paper we present a general expression describing the peak broadening effect on molecular weight averages measured during the elution of a polymer in GPC. This expression is valid for nonlinear column calibration and nonuniform Gaussian spreading across the chromatogram. Comparison is made with analytical relationships derived by Yau, Marais, Hamielec and Netopilik. The methodology developed as an extension of the Pierce and Armonas method is applied to a model system and to elution data of dextrans.     

Prediction of polyethylene melt rheological properties from molecular weight distribution data obtained by gel permeation chromatography

A method is presented for predicting rheological characteristics, such as shear dependent (non-Newtonian) viscosity and components of linear oscillatory (complex) response functions for polyethylene melts from molecular weight distribution data obtained from gel permeation chromatographic (GPC) analysis. The results are compared with measured values of the rheological functions obtained from a variety of instruments over an extensive range of shear rates-and frequencies. The agreement between predicted and measured rheological functions is quite good for high density resins. However, for a low density resin the agreement is not as good, although still reasonable over a considerable range of conditions. It is concluded that the quality of the GPC data is the key factor in the degree of success of the method.     

Influence of trimethylsilylation and detrimethylsilylation on the molecular weight of chitin: Evaluation of viscometry and gel permeation chromatography for molecular weight determination

In view of the high potential of trimethylsilylated chitin as a reaction precursor, the influence of trimethylsilylation and detrimethylsilylation on the molecular weight characteristics has been studied. Chitin was trimethylsilylated, and the product was detrimethylsilylated to regenerate chitin. The molecular weights of the original and regenerated chitins were determined by viscometry and GPC. The viscosity measurements, with either an Ubbelohde or a rotational viscometer, gave highly reproducible values, which were quite similar to each other. The molecular weight of the regenerated chitin was found to be a little over a half that of the original chitin despite after the silylation-desilylation reactions. GPC also supported a similarly low extent of main chain scission. These results indicate that the silylation-desilylation reactions are reproducible without a significant damage to the chitin main chain, and both viscometry and GPC have proved reliable in elucidating the molecular weight characteristics. Trimethylsilylation of chitin can thus be conveniently used as a key intermediate for further controlled modification reactions to prepare well-defined derivatives.     

Polymer reactors and molecular weight distribution. VII. Further development of gel permeation chromatography

The results of an investigation into molecular weight and resolution calibration of a gel permeation chromatograph are reported. Effects of sample amounts and solvent flow rate were observed. Severe skewing and tailing of the standard chromatograms were observed at 2.0 ml/min flow rate, relative to 1.0 and 3.0 ml/min. Resolution calibration by flow reversal was inadequate when skewing and tailing or sample impurity effects were significant. Differential molecular weight distributions (MWD) of broad-distribution polystyrenes were compared for four methods of resolution correction. Inconsistent oscillations were observed in the MWD's at low resolutions and higher molecular weights. None of the methods was completely adequate in accounting for skewing and tailing.     

溶解时间对凝胶渗透色谱法测定PVC分子质量的影响

介绍了应用凝胶渗透色谱法测定PVC分子质量的方法,讨论了常温下四氢呋喃溶解PVC时间对PVC分子质量及分子质量分布测定结果的影响。结果表明：PVC的溶解时间越长,测得的数均分子质量和重均分子质量越大,分子质量分布越窄;聚合度低的PVC比聚合度高的PVC受溶解时间影响更大些。     

Block copolymer molecular weight determination via gel permeation chromatography: Choosing a combining rule

We present a method for accurately determining the true molecular weights of narrow‐distribution block copolymers, using only a basic gel permeation chromatograph (GPC) equipped with a refractive index detector and calibrated with polystyrene standards. Our approach is based on the well‐known observation that GPC calibration curves for different homopolymers in good solvents are essentially parallel, allowing the curves for different polymers to be described by simple hydrodynamic equivalence ratios r_B versus polystyrene. We present values of r_B, in both toluene and tetrahydrofuran, for various polydiene and hydrogenated polydiene homopolymers commonly incorporated into commercial styrenic block copolymers. These values of r_B must be combined to yield the hydrodynamic equivalence ratio of the block copolymer, from which the block copolymer's true molecular weight can be determined. Three combining rules proposed in the literature are tested against a series of symmetric polystyrene–polybutadiene diblock copolymers of varying molecular weight. A simple linear combining rule accurately represents the results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2056–2069, 2001     

Molecular weight distribution of phenol-formaldehyde resols by high performance gel permeation chromatography

Resol resins are particularly difficult to characterize with respect to molecular weight because of the large amounts of caustic soda (10–20% w/w) which they contain. A method is described for solubilizing these materials using trichloroacetic acid, such that molecular weight distribution can be measured using a normal gel permeation chromatography system with μ-Styragel columns and tetrahydrofuran as solvent.     

Molecular weight distribution of polyphenylene sulfide by high temperature gel permeation chromatography

Poly(phenylene sulfide) (PPS) has been characterized using a novel high temperature gel permeation chromatograph (GPC). Samples were injected in slurry form at ambient temperature, and redissolved by an in-line precolumn heater at 250°C. A viscometer consisting of a capillary tube with inlet and outlet taps connected to a sensitive differential pressure transducer was used as sole detector, with deflections converted to concentration using the column calibration. Columns and viscometer were operated at 210°C. Universal calibration was carried out using intrinsic viscosity/molecular weight relations for polystyrene and PPS, determined by light scattering. Satisfactory operation was confirmed by agreement between intrinsic viscosity calculated from GPC with independently measured values, and comparisons with melt flow data. Samples of PPS tested were found to be of relatively narrow distribution, with M_w/M_n typically less than two.