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.     

The determination of the addition variation and geometrical isomerism of a polybutadiene as a function of molecular weight by preparative gel permeation chromatography and infrared analysis

The addition variation, 1,2 and 1,4 units, and the geometrical isomerism, 1,4-cis and 1,4-trans units, of a fractionated polybutadiene were determined as a function of molecular weight using preparative gel permeation chromatography followed by infrared analysis of the fractions. Both the addition variation and geometrical isomerism remained essentially constant across the molecular weight distribution.     

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     

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。     

Multiple detectors for molecular weight and composition analysis of copolymers by gel permeation chromatography

The use of a single detector in gel permeation chromatography (GPC) for samples of varying composition leads to erroneous conclusions. With certain simplifying assumptions, a gel permeation chromatograph equipped with properly selected dual detectors yields composition and molecular weight distribution information that is meaningful. Examples discussed are a mixture of homopolymers and a sample supposed to have been a styrene–butadiene block copolymer. The ultraviolet absorption is used in conjunction with the refractive index trace to give qualitative information that is much more informative than could be obtained with one detector. Calibration of the relative responses of the detectors to each of the components of the mixture is described, and these calibrations are used to calculate point-by-point composition, molecular weights, and molecular weight averages.     

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.     

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。     

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.     

凝胶渗透色谱法测定高黏度PET切片的分子质量分布

利用凝胶渗透色谱柱G4000HXL、G3000HXL(两柱串联),紫外检测系统测定高粘度切片的分子质量分布速度快,重复性好,实验数据点均落在直线上,线性良好,满足直线方程lgM=a+btR。与常规切片比较,高黏度切片分散系数小。可以依据分子质量分布来合理地选择原料和加工条件。     

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.     

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.     

凝胶色谱法测试PVC树脂平均分子质量及分子质量分布

叙述了凝胶色谱法的测试原理,介绍了用凝胶色谱测试PVC树脂平均分子质量及分子质量分布的方法。     

凝胶色谱法在聚丙烯分子量及分子量分布测定中的应用

根据聚丙烯在凝胶色谱柱上的淋洗特点,确定了测定其分子量及分子量分布试验条件;采用示差和黏度双检测凝胶色谱系统,利用普适校正方法,不需要Mark常数K、α值,可直接测定聚丙烯分子量分布并给出分子量分布曲线;采用统计方法计算数均分子量、重均分子量、黏均分子量,可以为课题研究提供一定的依据和指导。     

Molecular weight determination of HTPB resins by vapor pressure osmometry (VPO) and gel permeation chromatography (GPC): The effect of calibration standards

GPC and VPO behaviours of HTPB samples have been examined in toluene employing polystyrene and polybutadiene standards. The results show that the molecular weights obtained depend on the nature of the calibration standards, particularly in the GPC analysis. Received: 7 October 1996/Revised: 19 December 1996/Accepted: 23 December 1996     

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.     

Method of calculating molecular weight distribution function from gel permeation chromatograms. II. Evaluation of the method by experiments

The calculation scheme for correcting the broadening effect due to imperfect resolution on gel permeation chromatograms was compared with actual performances of a gel permeation chromatography (GPC) column. The experiment consisted of fractioanting a high-density polyethylene on a GPC unit and then determining the chromatograms of the cuts collected. The chromatograms of the cuts were also computed from the starting chromatogram using experimentally determined resolution factors. The degree of agreement between the calculated and experimental chromatograms of the cuts shows convincingly that the previously proposed calculation scheme is satisfactory for the treatment of GPC data.     

Column fractionation of polymers. VII. Computer program for determination of molecular weight distributions from gel permeation chromatography

Gel permeation chromatography produces a type of differential molecular weight distribution directly and rapidly. Conversion of these data to conventional molecular weight distributions and plots of distributions is time-consuming. A computer program is described to perform these operations readily. Input data from the automated chromatograph, elution volume, and recorder deflection are converted to unit sensitivity and base line corrections applied. The curve is then numerically integrated and a calibration curve used to convert elution volumes into molecular weights. Various calibration curves can readily be introduced into the program. The output, in addition to tabulation of cumulative and differential molecular weight distributions, contains values of M?_n, M?_v, M?_w, M?_z, and M?_z+1. Importantly, a reduced absolute area, i. e., area computed for unit sensitivity on a unit concentration basis, is tabulated. An additional time-saving eature is the printing out of differential and cumulative molecular weight distribution curves and of a differential histogram.