Determination of molecular weight averages and molecular weight distribution by g.p.c. of N-trifluoroacetylated polyamides

To determine their molecular weight averages and molecular weight distribution, N-trifluoroacetylated (TFA) polyamides are studied using gel permeation chromatography in tetrahydrofuran at 25°C. Several calibration methods (calibration with polydisperse standards, universal calibration) are tested; among these, direct calibration of M_w of polydisperse samples vs. peak maximum of the corresponding g.p.c. chromatogram leads to the best results. Calculated molecular weight averages of nylon 6-TFA and Trogamid^R-TFA are compared with data from light scattering, viscometry and osmometry.     

Comparison of molecular weight distribution models for polymers characterized by g.p.c.

A semi-empirical model which employs polynomials based on general free radical polymerization kinetics, is developed to describe the molecular weight distribution data as well as to evaluate the average molecular weights of a variety of commercial thermoplastics including polystyrene, poly(methyl methacrylate) and low density polyethylene. These novel expressions are equally applicable to a natural rubber sample with a bimodal distribution. Least-squares methods for the classical Schulz and Flory distribution functions are introduced to handle the g.p.c. data of the above polymers. Comparison of the results collected from various analyses indicates clearly that the polynomial model is the most versatile one in the sense that it can be utilized to smooth out satisfactorily the molecular weight distribution data of many polymers. In general, the Wesslau distribution function is particularly good for the highly branched polyolefin and the Schulz model is fairly effective for the addition polymers of moderately sharp molecular weight distribution, presumably with $\text{M}\text{?}{}_{\mathrm{<mtext>w</mtext>}}\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}\text{=3.0}$. However, the Flory and Tung distributions are found to be rather inferior in the present studies. On the basis of the current findings, a new procedure is suggested to facilitate the computations of the true average molecular weights from g.p.c. data directly.     

链长法测定多聚磷酸中磷酸的含量

链长法是利用多聚磷酸在未水解时以氢氧化钠溶液为滴定溶液,用自动电位滴定仪滴定,并记录滴定曲线,根据曲线上的两个拐点处所消耗的氢氧化钠的体积,计算多聚磷酸中磷酸的含量。该法样品处理和分析过程简单、快速、准确、成本低,能满足多聚磷酸生产和产品检验的要求。     

Modeling of sequence length distribution for olefin copolymerization with vanadium-based catalyst

Some thermodynamic and mechanical properties of a polyolefin, such as the melting temperature and the rigidity, are dependent on the nature of its sequence distribution. Accurate modeling of sequence length distribution (SLD) is important in precisely tuning and optimizing the properties of polymers produced. In this article, we proposed a model to predict the molecular weight distribution (MWD) and SLD for olefin copolymerization with vanadium-based catalyst. Due to the 2,1-insertion of α-olefin with vanadium-based catalyst, the SLD is expressed by uninterrupted methylene sequence distribution instead of conventional triad sequence distribution. To obtain a reliable model, parameter estimation with experimental data is first conducted. The SLD model along with the estimated kinetic parameters can be used to predict unmeasurable sequence length fraction. For the experimental conditions studied, the average methylene sequence length is predicted to change from 10 to 4 units as the propylene/ethylene mole feed ratio increases from 1.1 to 3.4.     

热裂解气相色谱法测定丁苯橡胶中苯乙烯含量

采用热裂解气相色谱法测定丁苯橡胶（SBR）中苯乙烯的含量。结果表明：理论苯乙烯含量与热裂解气相色谱法中特征峰的相对峰面积比呈良好的线性关系,相关因数为0.998 9;经标准曲线校正后的苯乙烯含量接近于真实值,计算结果的相对误差小于3%,测定结果的相对标准偏差在2%以内。该试验方法操作简单,重复性和再现性好,准确 度高。     

Molecular characterization of sodium poly(acrylate) by an aqueous g.p.c./LS method

The molecular characterization of a commercial sample of sodium poly(acrylate) (NaPA) has been carried out by a g.p.c./LS method in 0.3 N NaCl at 25°C. The sample is fractionated into eight fractions. The agreements between the weight-average molecular weights of the NaPA fractions determined by light scattering and those measured directly by the g.p.c./LS method are excellent. Universal calibration is established for both the standard poly(ethylene oxide) and the NaPA fractions. The degree of branching for the fractions with high molecular weights are estimated using the experimental results obtained by the g.p.c./LS method.     

High performance g.p.c. with crosslinked polystyrene gels: influence of particle size distribution

Spherical crosslinked polystyrene gel particles have been separated by air classification into fractions having average particle diameters in the range 10–40 μm. The particle size distributions have been shown to be narrow by Coulter Counter measurements. G.p.c. column performance improves as the average particle diameter decreases and columns packed with gel fractions having a number-average particle diameter below 20 μm give plate counts in excess of 3000 plates per foot. Plate height results as a function of eluent flow rate suggest that chromatogram broadening due to mobile phase dispersion is reduced in columns packed with spherical particles having a narrow size distribution.     

丁苯橡胶的微观结构表征方法研究（轮胎会）

介绍了折光法、紫外光谱法、裂解气相法、核磁共振法、红外光法等5种常见的丁苯橡胶微观结构表征方法。其中,折光法、裂解气相色谱法和紫外光谱法能够测定SBR的苯乙烯含量,核磁共振法和红外光谱法都能够测定全部四种微观结构;五种测试方法中,核磁共振法测试重复性最好,裂解气相色谱法最差;裂解气相色谱法样品处理最简单,紫外光谱法样品处理最繁琐;折光法和核磁共振法无需标准品标定,其余三种方法需使用已知结构的SBR标准品标定。     

丁苯共聚物示差折射率的测定

研究了丁苯共聚物示差折射率 (dn/dc)测定方法。结果表明 ,丁苯共聚物的微观结构与组成对其表观dn/dc的影响很大 ;序列结构、测定温度、相对分子质量等因素对dn/dc的测定结果均有影响 ,但影响较小。实际测定表明 ,所测表观dn/dc与计算值基本符合     

The effect of the mixed external donors on the sequence length distribution of polypropylene

The effects of different mixed external donors on the crystallization behavior and sequence length distribution of polypropylene prepared by MgCl₂‐supported TiCl₄ Ziegler–Natta catalyst were studied through successive self‐nucleation and annealing (SSA) technique. The SSA results show that the crystallization ability and the relative contents of long isotactic sequence length gradually increase with the increase of the relative component of Donor‐1 (cyclohexylmethyldimethoxysilane, dicyclohexyl(dimethoxy)silane, and dipiperidinedimethoxysilane) in the different mixed external donors when the ratio of the mixed external donors/Ti (Si/Ti) is unchanged. The thickness distribution of lamellar also becomes broader, indicating the sequence length distribution of polypropylene gets broader. The crystallization ability and the relative contents of long isotactic sequence length of polypropylene prepared by the mixed cyclohexylmethyldimethoxysilane and n‐propyltriethoxysilane (C? N) external donors are lowest. However, the effect of the mixed dicyclohexyl(dimethoxy)silane and n‐propyltriethoxysilane (H? N) and the mixed dipiperidinedimethoxysilane and n‐propyltriethoxysilane (Py? N) external donors on the crystallization ability and sequence length of polypropylene are more significantly. Especially, the relative content of long isotactic sequence length increases sharply from 0.2 to 27.5% in the polypropylene chain of sample prepared by the mixed Py? N external donors when the proportion of Donor 1 is running up to 90%. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Determination of non-spherical particle size distribution from chord length measurements. Part 1: Theoretical analysis

In this paper, extensive theoretical studies are described on two important issues in translating a chord length distribution (CLD) measured by FBRM instrument into its particle size distribution (PSD) including PSD-CLD and CLD-PSD translation models for general non-spherical particles. Analytical solutions to calculate the PSD-CLD models for spherical and ellipsoidal particles are developed. For non-spherical particles, a numerical method is given to calculate the PSD-CLD model. The iterative non-negative least squares (NNLS) method is proposed in the CLD-PSD model, because of its many advantages converting measured CLD into its PSD, such as insensitivity to measurement noise and particle shape. The effectiveness of the proposed methods is validated by extensive simulations.     

Determination of non-spherical particle size distribution from chord length measurements. Part 2: Experimental validation

In this paper, the theory on the translation of a measured chord length distribution (CLD) into its particle size distribution (PSD), which was developed in the first part of this study [Li and Wilkinson, 2005. Determination of non-spherical particle size distribution from chord length measurements. Part 1: theoretical analysis. Chemical Engineering Science 60, 3251-3265], has been validated using experimental results. CLDs were measured using the Lasentec focused beam reflectance measurement (FBRM) with three different materials, spherical ceramic beads and non-spherical plasma aluminium and zinc dust particles. Meanwhile, the particle shape and PSD of each material were also investigated by image analysis (IA). Comparison of the retrieved PSDs with the measured PSDs by IA shows that the PSD can be retrieved from a measured CLD successfully using the proposed iterative nonnegative least squares (NNLS) method based on the PSD-CLD model.     

硫化剂TMTD硫化SBR胶料交联密度的测定

研究二硫化四甲基秋兰姆(硫化剂TMTD)用量对SBR胶料交联密度的影响以及溶剂和试验方法对交联密度测定结果的影响.结果表明:随着硫化剂TMTD用量的增大,SBR胶料的交联密度增大;在交联密度较大时,以甲苯为溶剂测定的交联密度结果偏小;抽提对交联密度测定结果基本无影响.     

鞘氨醇单胞菌脱硫丁苯橡胶胶粉填充丁苯橡胶性能的研究

利用鞘氨醇单胞菌对丁苯橡胶(SBR)胶粉进行脱硫,对比研究SBR胶粉和脱硫SBR胶粉填充SBR胶料的性能。结果表明:鞘氨醇单胞菌不仅可使硫交联键断裂,也可使橡胶主链上的部分碳-碳双键断裂。与SBR胶粉填充的SBR胶料相比,脱硫SBR胶粉填充SBR胶料的转矩和表观交联密度减小,拉伸强度和拉断伸长率增大,邵尔A型硬度和撕裂强度保持不变,阿克隆磨耗量减小,脱硫SBR胶粉与SBR基体结合较紧密,动态滞后损失较小。     

Determination of monomer sequence distribution in EPDM by 13C‐NMR: Third monomer effects

The methods for sequencing ethylene–propylene copolymers (EPMs) by ¹³C‐NMR were extended to account for third monomer effects. The equations for calculating the ethylene content and monomer sequence distribution in EPMs were corrected for the presence of the third monomers 1,4 hexadiene, 2‐ethylidene‐5‐norbornene, and 5,8‐dicyclopentadiene that display resonances that overlap with the main chain EPM carbons. These corrections dramatically reduce the standard deviation among equivalent calculation methods. We also examined the effects of experimental conditions on the sequencing data including the choice of solvent, Cr³⁺ doping, and the presence of the nuclear Overhauser effect. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 523–530, 1999     

交流示波极谱滴定法测定废电镀液中的银

采用交流示波滴定法，以二乙基二硫代氨基甲酸钠为滴定剂，稀硝酸为解蔽剂，乙酸钠和聚惭烯醇为极谱底液测定废电镀液中的银含量，讨论了聚惭烯醇，乙酸钠，滴定剂，pH值和仪器等因素对测定结果的影响，该方法误差小，银回收率为97．50％－101．25％，可满足废电镀液中银的测定要求。     

Determination of the specific heat of polystyrene by d.s.c.

The specific heat of various polystyrenes has been measured by d.s.c. using two methods—calibrating with heat of fusion of indium and using sapphire as an external standard. The effect of such variables as sample weight, heating rate and calorimeter sensitivity on the measurements are considered. In general, a limiting accuracy of 2% and temperature variations of 6K are imposed by these methods, and the detector response of the calorimeter.     

校准曲线法测定SBR硫化胶的交联密度及交联键结构

建立了SBR纯胶和N326炭黑增强（60份）两体系的化学交联密度（Xc)-溶胀因子（fs)校准曲线，并用溶胀法测试了两体系的化学交联密度及交联键结构。结果表明，溶胀法测出的Xc要比Shirley Lee等提出的“每消耗3mol二硫化四甲基秋兰姆（TMTD）分子产生1mol交联键”所预测的数值要低。运用建立的校准曲线测定了不同硫黄用量硫化体系（CV，semi-EV,EV)的交联密度，并用溶胀法测其交联密度及交联键类型，对两结果进行了比较。     

流变学方法测定UHMWPE树脂的相对分子质量及其分布

相对分子质量及其分布是超高相对分子质量聚乙烯(UHMWPE)树脂的一个重要指标。采用流变学手段测定了UHMWPE树脂的重均相对分子质量(M_w)及其分布,并与凝胶渗透色谱(CPC)法测试结果进行对比。结果表明:利用傅里叶变换将应力松弛实验的时域信号数据转换为频域信号数据,再结合流变仪频率扫描的结果得到较为完整的流变学数据,然后将储能模量和损耗模量转换到松弛谱得到松弛模量,可以计算出UHMWPE树脂的M_w及其分布;流变学方法测定UHMWPE的M_w的变化趋势与GPC方法结果相同;采用流变学方法测定UHMWPE树脂的M_w及其分布,速度快、重复性高,且不需要溶剂来溶解UHMWPE树脂。