The effect of precipitation on the molecular weight distribution of cellulose tricarbanilate

The effect of precipitation on the molecular weight distributions of cellulose tricarbanilate (CTC) samples prepared from α-pulp, hydrolyzed α-pulp, and Avicel was determined using size exclusion chromatography (SEC). Precipitation of the CTC samples in methanol resulted in the loss of a low molecular weight fraction accounting for 26% of the weight of the hydrolyzed α-pulp, 20% of the Avicel, and 5% of the α-pulp. Precipitation in a methanol/water mixture resulted in less fractionation; in this case, however, the reaction byproducts were also precipitated. These results indicate that the molecular weight distribution of precipitated CTC may not accurately reflect the molecular weight distribution of the original cellulose. SEC analysis of the nonvolatile products from the carbanilation reaction offers a simple method for determining the complete molecular weight distribution of this cellulose derivative.     

Application of the weibull distribution function to the molecular weight distribution of cellulose

The molecular weight distribution of a linear homologous polymer is usually obtained empirically for any particular sample. Sample-to-sample comparisons are made in terms of the weight- or number-average molecular weights and graphic displays of the distribution curves. Such treatment generally precludes data interpretations in which a distribution can be described in terms of differing proportions of mixed populations. However, a statistical continuous univariate distribution function such as the Weibull can be applied to the molecular weight distributions measured for cellulose nitrate samples. The size distributions of samples degraded under some gentle stress may then be indentified as consisting of differing proportions of populations with similar characteristic distributions. Analyzing data in this way should permit interpretation of the results as for breakdown of oligomers in a small-molecule system.     

Analysis of molecular weight distribution of purified cellulose pulp

The molecular weight distribution of purified cellulose pulp is analyzed by using empiric distribution functions. The data are also analyzed by the direct binomial method and the results are compared with those obtained by the method of Beall.     

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。     

Prediction of molecular weight distribution of cellulose by using the rheological method

In this article, a rheological method that can predict the molecular weight distribution (MWD) of polymer was introduced. Using this method, the MWDs of four cellulose samples were compared from rheological data of the cellulose / N‐methyl morpholine N‐oxide (NMMO) / H₂O solutions. The MWDs of cellulose also were determined by gel permeation chromatography (GPC) calibrated with narrow distribution polystyrene standards, using 0.5% lithium chloride (LiCl) in N,N‐dimethylacetamide (DMAc) as the eluent. Comparison of the results from rheology and GPC showed that the MW and MWD of cellulose could be roughly inferred from their rheological data. Although the differential MWD obtained from the rheological method was bell shaped and can not reflect the fine characteristics of cellulose as GPC, it may be feasible to compare the MWDs of cellulose by using the rheological method. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 598–603, 2004     

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。     

Prediction of molecular weight scale and molecular weight distribution of cellulose using a rheology‐based method

Prediction of MW scale and MWD of cellulose by means of a rheology‐based method is developed. In this method, for the cellulose/NMMO·H₂O solution, it is assumed that the cellulose MW values calculated by the Rouse terminal relaxation time can be regarded as the peak MW on the MWD curves of cellulose. Consequently, it is realized that the reciprocal of the frequency is converted to the MW scale, obtaining MWD scale curves of cellulose. Meanwhile, the obtained results are compared with those measured by the GPC method. The comparison shows that the calculated peak MW values are approximately equal, the calculated PDI values and MWD curves have the same trends. Consequently, it may be feasible to compare the MW scale and MWD of cellulose by using the rheology‐based method. In addition, the rheology‐based method is simple and fast. Therefore, it is a useful and easy way to analyze the MW scale and MWD of cellulose in the fiber industry. POLYM. ENG. SCI., 48:102–106, 2008. © 2007 Society of Plastics Engineers     

Modification of cellulose powder surface by grafting of polymers with controlled molecular weight and narrow molecular weight distribution

To modify cellulose powder surface, the grafting of polymers with controlled molecular weight and narrow molecular weight distribution onto the surface by the termination of living polymer cation with amino groups introduced onto cellulose powder surface was investigated. The introduction of amino groups onto cellulose powder surface was achieved by the treatment of cellulose powder with isatoic anhydride. It was found that cellulose powder having amino groups are readily reacted with living poly(2‐methyl‐2‐oxazoline) (polyMeOZO) cation, which was generated by ring‐ opening polymerization with methyl p‐toluenesulfonate as an initiator, and polyMeOZO with controlled molecular weight and narrow molecular weight distribution was grafted onto the surface. By the termination of living poly(isobutyl vinyl ether) (polyIBVE), which was generated by the polymerization with HCl/ZnCl₂ initiating system, with amino groups on cellulose powder, polyIBVE was also grafted onto the surface. The mole number of grafted polymer chain on cellulose powder surfaces decreased with increasing molecular weight of the living polymer cation, because of increasing steric hindrance with increasing molecular weight of living polymer cation. Wettability of cellulose powder surface to water was found to be controlled by grafting of hydrophilic or hydrophobic polymer onto the surface. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 515–522, 2000     

Method of calculating molecular weight distribution function from gel permeation chromatograms

An integral equation taking account of the limited resolution of the chromatographic columns is given to relate the gel permeation chromatogram and the true molecular weight distribution function. Three approaches to solve the integral equation are described. The first approach provides a special solution for the log-normal molecular weight distribution function; the other two approaches give two numerical solutions for general distribution functions. The use of these solutions in the treatment of gel permeation chromatography data is discussed.     

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.     

Determination of the molecular weight distribution of polyisoprene by random scission

cis-Polyisoprene in dilute solution in toluene (plus antioxidant) undergoes random scission when exposed to γ-radiation. The possibility of using this scission in a method to assess the width of the molecular weight distribution of the polymer has been explored and found potentially useful in situations where conventional methods provide little information.     

Determination of the impact of cellulose ester molecular weight on the drying behavior of automotive refinish basecoats

In the case of automotive refinish basecoat formulations, anti-sag and dry-to-touch are very important requirements. A series of experiments were outlined to investigate the impact of cellulose acetate butyrate (CAB) on the drying behavior of refinish formulations using thermogravimetric analysis (TGA). The goal was to ascertain whether the chemical nature and the molecular weight of the cellulose ester had any impact on solvent losses during the film formation process. Automotive refinish formulas were prepared containing different grades of CAB. Two approaches were adopted for the initial set of experiments. The first batch of samples was prepared at the same application viscosity (iso-viscosity) which meant that the solids level varied depending on the molecular weight of CAB that was used. The second set had identical solids level (iso-solids) which in turn caused the viscosity to be dependent on the grade of CAB.     

碱木素分子量及其分布的GPC表征

采用水溶性凝胶渗透色谱测定了碱水素的分子量特征,并对影响分子量分布测定的因素进行了探讨。结果发现,所用流动相的酸度对碱木素在凝胶色谱柱上可能发生的吸附影响比较显著。当流动相的碱性不够时,碱水素会发生吸附,并且大分子量木素优先被吸附,当pH升至12时可消除吸附现象。流动相的离子强度增大亦可以部分消除木京的吸附。     

Change in molecular weight distribution by elution of polymers from PVA cast gel

Poly(vinyl alcohol) (PVA) cast gels with high degrees of polymerization and hydrolysis were prepared at room temperature. After sufficient exchange of the outer solvent by fresh pure water, the gel was re-dissolved in pure water at a high temperature. Using this solution, the cast gel was prepared again. This re-dissolution process was repeated again, and a third cast gel was prepared. During each swelling process after each cast-drying process, the amount of elution from the gel was measured and the molecular weight distributions of PVA in the gel as well as in the outer solvent were quantitatively evaluated. The molecular weight distribution of the eluted PVA was found to depend on that of the PVA in the gel; the average molecular weight gradually increased as the re-dissolution process was repeated, while the polydispersity indices of both the PVA from the gel and the eluted PVA decreased.     

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.     

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。