氯化聚丙烯甲苯溶液的特性黏数及其黏均分子量

分别用乌氏黏度计和旋转黏度计测定了氯化聚丙烯甲苯溶液的特性黏数和黏度,把特性黏数和黏度进行关联,发现ηsp/C与浓度C(ml/g)的关系用多项式ηsp/C=[η]+k1[η]2C+k2[η]2C2拟合,可以得到很好的结果。并且用特性黏数和Mark-Houwink方程求出了不同氯化聚丙烯(CPP)的黏均分子量。     

Relation between intrinsic viscosity and molecular weight

The connection between intrinsic viscosity and number-average and weight-average molecular weight has been revealed by calculations from distribution curves. Log-normal distributions, and moderate variations thereon, were chosen as typical for polystyrene and other thermoplastics. Intrinsic viscosity and number-average molecular weight are unlikely to be related because of the highly disturbing effect of small variations in molecular weight distribution. Conversely, intrinsic viscosity is a good practical measure of weight-average molecular weight up to a ratio of 10 for weight-to-number average.     

Correlating mooney viscosity to average molecular weight

Copolymers of styrene and butadiene of the same chemical conposition, but widely different molecular weight distributions, were characterized by gel permeation chromatography. A very good correlation was obtained between the logarithm of the Mooney viscosity and the logarithm of the geometric mean of the number- and weight-average molecular weights. Instead of this molecular weight average, one can equally well use the very convenient “Av log M,” which is a weight-average molecular weight, using a logarithmic molecular weight scale. This correlation makes it possible to predict the Mooney viscosity from GPC data with a precision of about 15% (± one standard deviation), independent of the molecular weight distribution of the polymer. The obtained correlation was much better than with either weight-average molecular weight or viscosity-average molecular weight with α = 0.67.     

Estimation of molecular weight averages from intrinsic viscosity

The weight-average molecular weight is estimated by an extrapolation technique based on a linear relation between the viscosity-average molecular weight M_v and a Mark–Houwink–Sakurada constant. This method may also be used to assess the unperturbed dimensions of polymers. If the M_v data are known with high accuracy, then the straight line may be stretched to reach the number-average molecular weight confidently. The slope of the linear plot is associated with the molecular weight distribution and as such can be utilized to compute the polydispersity index.     

The effect of shear rate on the molecular weight determination of acrylamide polymers from intrinsic viscosity measurements

The rheological response of dilute solutions of high molecular weight polyacrylamides at low shear rates has been measured using a capillary viscometer that provided for a fivefold variation in shear rate at each concentration. The non-Newtonian effects were found to be significant for polyacrylamides with number-average molecular weights exceeding 10⁶. The molecular weight average–intrinsic viscosity relationship most widely used in the literature, [η] = 6.80 × 10^?4M , was found to be valid when [η] was measured at high shear rates where the polymer solutions approached Newtonian behavior. A new relationship was developed relating M _n to the intrinsic viscosity extrapolated to zero shear rate.     

Relationship of intrinsic viscosity of polymer solutions to molecular weight

An equation derived by Han relating intrinsic visocity to molecular weight of a polymer has been fitted to experimental data over a large range of molecular weight. Excellent fits were obtained although the Mark-Houwink equation did not fit the data over the complete molecular weight range. Han's equation may be fit to intrinsic viscosity data over a moderate range of molecular weight, and is shown to then accurately predict the intrinsic viscosities for molecular weights outside this range. A method is given to compute the two parameters of Han's equation from the Mark-Houwink parameters of a polymer in a solvent.     

Dependence of intrinsic viscosity and molecular size on molecular weight of partially hydrolyzed polyacrylamide

As a typical water-soluble polymer, ultra-high molecular weight (UHMW) partially hydrolyzed polyacrylamide (HPAM) has been widely used in various industries as thickeners or rheology modifiers. However, precise determination of its critical physical parameters such as molecular weight, radius of gyration (R_g) and hydrodynamic radius (R_h) were less documented due to their high viscosity in aqueous solution. In this work, the molecular structure of five UHMW-HPAM samples with different MW was elucidated by ¹H and ¹³C NMR spectroscopy, and their solution properties were characterized by both static and dynamic light scattering. It is found that all the second virial coefficient (A₂) values are positive and approaching zero, indicating of a good solvent of 0.5 M NaCl for UHMW-HPAM. The weight-average molecular weight (M_w) dependence of molecular size and intrinsic viscosity [η] for these series of HPAM polymers with MW ranging from 4.81 to 15.4 × 10⁶ g·mol⁻¹ can be correlated as R_g = 3.52 × 10⁻²M_w^0.51, R_h = 1.97 × 10⁻²M_w^0.51, and [η] = 6.98 × 10⁻⁴ M_w^0.91, respectively. These results are helpful in understanding the relationship between molecular weight and coil size of HPAM polymers in solution, and offer references for quick estimation of molecular weight and screening of commercial UHMW-HPAM polymers for specific end-users.     

Molecular weight and polydispersity measurements of polystyrene by quasielastic light scattering

The molecular weight and polydispersity of a polydisperse polystyrene sample was measured by quasielastic light scattering. The molecular weight distribution of the polymer was represented by the Schultz distribution. The weight average molecular weight and polydispersity of distribution was adjusted until the quasielastic light scattering spectra calculated for the distribution agreed with the measured spectra. The calculation was repeated using the logarithmic normal distribution for the polymer. The calculated value of the weight average molecular weight is accurate and insensitive to the assumed molecular distribution function. However, the calculated values of the polydispersity are only of fair accuracy. Thus quasielastic light scattering gives values of the weight average molecular weight at least as accurate as elastic light scattering and gives a crude estimate of the polydispersity of the polymer.     

Comments on the accuracy of zero shear intrinsic viscosity of high molecular weight polyacrylamide

The intrinsic viscosity of a polymer is traditionally measured with a capillary tube viscometer where the shear rate range is moderately high. Such method is valid when the polymers are non-ionic and have low to moderate molecular weight. The viscosity-shear rate curves obtained for dilute aqueous solutions of two high molecular weight polyacrylamides using two rotational viscometers indicate a strong shear-dependent viscosity in the medium to high shear rate regions. The zero shear intrinsic viscosity of the polymers determined by extrapolation from the high shear rate region to the zero shear condition may result in large errors. Its implication in predicting the molecular weight of polymers using the Mark-Houwink-Sakurada equation is discussed. A rheological equation for intrinsic viscosity as a function of shear rate is proposed.     

Number‐average molecular weight of branched polymers from SEC with viscosity detection and universal calibration

BACKGROUND: Number‐average molecular weight, M?_n, is an important characteristic of synthetic polymers. One of the very few promising methods for its determination is size‐exclusion chromatography (SEC) using on‐line viscometric detection and assuming the validity of the universal calibration concept. RESULTS: We have examined the applicability of this approach to the characterization of statistically branched polymers using 22 copolymers of styrene and divinylbenzene as well as 3 homopolymers of divinylbenzene with various degrees of branching. SEC with three on‐line detectors, i.e. concentration, light scattering and viscosity, enables us to evaluate experimental data by various computational procedures yielding M?_n and weight‐average molecular weight, M?_w. Analysis of the results has shown that the universal calibration theorem has limited validity, apparently due to the dependence of the Flory viscosity function on the molecular shape, the molecular weight distribution and the expansion of molecules. CONCLUSION: For complex polymers, the universal calibration, i.e. the dependence of the product of intrinsic viscosity and molecular weight, [η]M, on elution volume, can differ in values of [η]M from those obtained for narrow molecular weight standards by 10–15%. The method studied is helpful for the determination of M?_n of polymers, in particular of those with very broad molecular weight distribution, such as statistically highly branched polymers. Copyright © 2008 Society of Chemical Industry     

The effect of viscosity on surface tension measurements by the drop weight method

Viscosity is one of the parameters affecting the measured surface tension, as fluid mechanics affects the measurement process using conventional methods. Several methods including the selected planes (SPM) and WDSM which combines the weight drop method (WDM) and SPM, are applied to surface tension measurement of high viscous liquids. Yet, none of them treats the viscosity effect separately. The current publication presents a simple, easy to apply empirical approach of satisfactory accuracy, for evaluation of surface tension of liquids having wide range of viscosities up to 10 Pa s. The proposed method is based on Tate's law and the “drop weight” method using calibration curves of known liquids having similar surface tensions but different viscosities. Drop weight of liquids having viscosity ≥0.05 Pa s, was found to be significantly affected by the liquid viscosity. The shape factor, f, of high viscosity liquids was found to correlate linearly with the logarithm of viscosity, pointing the importance of viscosity correction. The experimental correlation presented in the current work can be used as a tool for the evaluation of surface tension for high viscosity liquids such as prepolymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

含侧氨基聚二甲基硅氧烷MHS方程的订正

通过测定含侧氨基聚二甲基硅氧烷聚合物的数均分子量和特性粘数,对MHS方程中的常数K和α进行了订正,得到的MHS方程表述为:[η]=3.21×10-4Mn0.66。     

Semi-empirical model for polyelectrolyte intrinsic viscosity as a function of solution ionic strength and polymer molecular weight

Elements of Odijk-Skolnick-Fixman and Yamakawa-Fujii polymer solution theories have been modified to create a new model that correlates flexible coil polyion intrinsic viscosity behavior with solvent and polymer properties. A new dimensionless viscosity is derived and is successfully related to the dimensionless ratio of Debye-Hückel screening length to polyion charge spacing and the degree of polymerization. The model has been applied to intrinsic viscosity data reported in the scientific literature and to data collected in our laboratory, all using sodium chloride solutions ranging in ionic strength. Multiple molecular weight fractions of six compositionally different polyelectrolytes were used to obtain 73 intrinsic viscosity versus ionic strength data points for model analysis. Regression analysis was applied to empirically determine the relationships between the dimensionless groups. The resulting model equation was found statistically adequate in describing the entire data set.     

Molecular weight and temperature dependence of intrinsic viscosity of polymer solutions

The molecular weight and temperature dependence of the intrinsic viscosity of polymer solutions have been predicted by combining the calculated radius of gyration, R_G, and hydrodynamic radius, R_H, with either the static empirical approach of Mandelkern—Flory or the dynamic argument of Weill—des Cloizeaux. It is found that experimental results can be successfully represented by the dynamic model for a range of five decades of molecular weight and temperature. The discrepancy between the calculated and experimental data at $\text{N ? N}{}_{\mathrm{т}}$ reveals the crudeness of the discontinuity at the temperature cut-off assumed by current temperature blob theory.     

Determination of intrinsic viscosity by single specific viscosity measurement

Single point determination of intrinsic viscosity saves considerable amount of time, effort and materials. Quite a few equations are available in the literature which require relative viscosity of the polymer solution at a single concentration for calculation of [η]. A comparative assessment of the applicability of two such equations and that of a proposed one has been made by using reported data as well as the practical data on viscosity of alkyd solutions in different solvents. It is inferred from the findings that, for good results from single point methods, the concentration should not be the sole criterion, as suggested by earlier workers; η_sp may also be considered as one of the criteria. The single point technique is found to be applicable to alkyd solutions in different solvents.     

A simple viscometric test for number average and weight average molecular weight of 12.6% N pyro nitrocellulose

In the poor solvent acetone/ethanol the viscosity of a 3% solution of 12.6% N pyro nitrocellulose is found to be related to the geometric mean of the number average and weight average molecular weights. The fractional increase in the viscosity of such a solution on the addition of lead ß-resorcylate is a function only of number average molecular weight. Once calibration has been made against osmotic pressure measurements and intrinsic viscosity, both number and weight average may be measured rapidly with an accuracy which is no less than that of the osmotic pressure and intrinsic viscosity measurements themselves.     

A method for determination of thermodynamic and solubility parameters of polymers from temperature and molecular weight dependence of intrinsic viscosity

An equation using the temperature dependence of intrinsic viscosity of a polymer was proposed for the determination of the partial molar entropy and enthalpy changes of the polymer for mixing in dilute solution. It was found that the partial molar entropy change of a polymer for mixing at a given temperature is proportional to the hydrodynamic volume or segment number of the polymer. The partial molar enthalpy change of the polymer for mixing was determined from the thermodynamic equilibrium property of polymer phases. The solubility or cohesion parameter of a polymer fraction was calculated by using the partial molar enthalpy change and repeat unit volume of the polymer. The solubility parameter of high molar mass polymer at a given temperature was determined by extrapolating solubility parameter values of polymer fractions to high molar mass by using the solubility parameter-segment number relation of polymer fraction. This relation gives a straight line. The solubility parameter of the polymer at a given temperature and the effective interchange energy parameter for polymer-solvent pair were obtained directly from the intercept and the slope of this line, respectively. These equations were applied to the intrinsic viscosity-temperature data of polystyrene fractions in decalin solutions, and polystyrene fractions in decalin, cyclohexane and dioctyl phthalate solutions at the theta temperatures and in toluene solutions at the given temperatures. The results obtained in this study coincide with the literature values. In addition, it was given a relation, which is derived from the blob theory for the temperatures above the theta point, for the estimation of the thermodynamic parameters of polymers for mixing.     

超高相对分子质量聚乙烯特性黏数的测试方法

采用毛细管黏度计法测定超高相对分子质量聚乙烯(UHMWPE)的特性黏数([η]),对[η]的准确测定的影响因素进行了探讨。结果表明:以十氢萘为溶剂,使用前进行蒸馏提纯;在配制UHMWPE溶液时,加入质量分数为0.2%的抗氧剂1010,按预溶胀、溶胀、溶解3步骤进行溶解,溶解温度150℃,溶解时间0.5 h,配制UHMWPE溶液浓度为100~600 mg/L;严格控制温度(135±0.2)℃,所测UHMWPE的[η]平行性较好,相对标准偏差为1.08%。