Molecular Weight Of Linear Polymer Research Articles

Determination of the Molecular Weight of Linear Polymers From Viscosity Measurements Carried out in the Solvent Mixtures

In this work polyvinyl acetate prepared by B. D. H Laboratory »Chemicals Di- vision has been used. The intirinsic viscosities have been determined in acetone-benzene mixtures of various percentâges. By using these intrinsic viscosity values the viscosity average molecular weights of the same polyvinyl acetate sample have been calculated from this relationship: [?]] = K' M»' (1) In this equation the values of K and a' are calculated from the following equations: K' = — Ki (1—fi)3 + K2 (1—fi)3 (2) a' = «ı fi + a2 ( 1—fı) (3) Where fi stands for the volüme fraction of one solvent in the solution. Kn aı and K2, a2 are constants for a given polymer-solvent system and temperature. The values of Kn aı and K2, a2 are given in the literatures [1, 2 ] for polyvinyl ace- tate-benzene and polyvinyl acetate-acetone systems. The values of the molecular weight abtained by this method are satisfactorily good within experimental errors. The benzene-acetone mixture is better than püre ben¬zene and acetone as solvent for the polyvinyl acetate. Especially the solution containing 20-40 % benzene is the most effective solvent for this polymer. Here polar and nonpolar parts of the polymer are respectively affected by acetone and benzene.

Gel permeation chromatography study of active centers in propylene oxide polymerization catalyzed by C3H5O3K3, C3H5O3K3–CaSO4, C3H5O3K3–crown ether, and C3H5O3K3–CaSO4–crown ether systems

AbstractGel permeation chromatography (GPC) is widely used to measure the molecular weights of linear polymers. A detailed analysis of high‐quality GPC data is an important source of information about the kinetics of a polymerization reaction. The living polymerization of epoxide demonstrates that the Poisson function is suitable for a molecular weight distribution description of polyether produced with catalysts containing a single type of active center. Therefore, poly(propylene oxide)s obtained by different catalytic systems, including C3H5O3K3, C3H5O3K3–CaSO4, C3H5O3K3–crown ether, and C3H5O3K3–CaSO4–crown ether, were characterized by GPC. The peaks obtained by GPC were resolved with a multi‐Poisson distribution function. This signifies that there might be multiple active sites instead of single site in these catalytic systems. The addition of calcium sulfate to the catalytic systems not only increased the molecular weight of the polyether but also effected the formation of the active sites. Furthermore, the polymerization of propylene oxide was processed in the presence of the aforementioned catalytic systems. Much useful information concerning the kinetic process of the polymerization was obtained from the GPC data with computer analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2100–2105, 2003

Molecular weight distributions of linear polymers: Detailed analysis from GPC data

AbstractThe GPC method is used widely to measure molecular weights of linear polymers. High‐quality GPC data contains detailed information on many aspects of the polymer's molecular weight distribution (MWD). This information can be extracted from the data using computer analysis. Equations have been derived for the two simplest MWD functions in the GPC coordinates: the Flory function (one growing polymer chain produces one polymer molecule), and for the case when two polymer radicals combine into one polymer molecule. The equations were used to analyze MWD of two classes of polymers. The first class includes polymers with narrow MWD: polyethylene, ethylene‐propylene and ethylene‐hexene copolymers, syndiotactic polystyrene, and radical polystyrene. The second class includes polymers with broad MWD: ethylene copolymers and polypropylene produced with heterogeneous, Ti‐based catalysts. The examples demonstrate that the resolution of complex GPC curves into their constitutents serve as an important source of information about kinetics of polymerization reactions. © 1995 John Wiley & Sons, Inc.

Molecular weight of linear polymer from storage modulus

Abstract In a previous work [1], using a binary blending rule, we had developed a numerical method to calculate the polymer molecular weight from the relaxation time spectrum of the terminal zone of stress relaxation modulus G(t). In this work, we separated the terminal zone of storage modulus G'(ω) from plateau modulus Gno and calculated the relaxation time spectrum H by using the second approximation formulas of Tschoegl [2]. The polymer molecular weight and molecular weight distribution was then obtained from H by using the same numerical method as was developed in the previous work [1]. The results calculated by this method are in good agreement with those measured from membrane osmometry, light scattering, GPC, etc.

Free volume model for molecular weights of polymers

A free volume model has been developed for determining molecular weights of linear polymers. It is based on the size of free volume cells in two geometries of poly (arylene ether ketone)s. Free volume cell sizes in test samples were measured using positron lifetime spectroscopy. The molecular weights computed from free volume cell sizes are in good agreement with the values measured by gel permeation chromatography, with a low angle laser light scattering photometer as the detector. The model has been further tested on two atactic polystyrene samples, where it predicted the ratio of their molecular weights with reasonable accuracy.

Molecular Weight of Linear Polymer from Transient Viscoelasticity

Molecular Weight of Linear Polymer from Transient Viscoelasticity

Poly(n‐butyl acrylate)/polystyrene interpenetrating polymer networks and related materials. III. Effect of grafting level and molecular weight in semi‐2 IPNs

AbstractA series of poly(n‐butyl acrylate)/polystyrene IPNs and semi‐1 IPNs with deliberately controlled graft levels were synthesized via a urethane chemical coupling method. Also prepared were a series of semi‐2 IPNs with the molecular weight of polymer II as the variable. The more highly grafted IPNs displayed poorly defined morphologies in which the domain structures were irregular and phase domain boundaries were characterized by fibrillar and interphase regions. A single glass transition peak was another feature of the more highly grafted IPNs. Polymer network II formed in the presence of linear polymer I results in morphologies dependent on the molecular weight of linear polymers. In the semi‐2 IPNs, polymer I molecular weights below Mv = 20,000 caused polymer I to behave like a plasticizer or a diluent. The domain sizes of semi‐2 IPNs agree with theoretical predictions developed by the present authors.

A method for the determination of number average molecular weights of linear polymers less than 5 000

A method for the determination of number average molecular weights of linear polymers less than 5 000

Equations for Calculating Chain Length Distributions in Polyphosphoric Acids and Polyphosphate Glasses

The Flory distribution of molecular weights of linear polymers resulting from the condensation of bifunctional monomers was used by Van Wazer to calculate the constitutions of thepoly phosphoric acids. Jost and Wodtcke proposed a modification to the Van Wazer approach for sodium phosphate glasses. By modifying and extending these ideas, it is shown that, by using a few empirical parameters, it is possible to calculate chain length distributions for polyphosphoric acids and polyphosphate glasses, which give a satisfactory fit to available data. These distributions are useful for smoothing and extrapolating data and for emphasizing deviations from the Flory distributions taken as “ideal”.

Estimation of the molecular weight of linear polymers by the thermomechanical method

Estimation of the molecular weight of linear polymers by the thermomechanical method

Thermomechanical Characterization of the Molecular Weight of Linear Polymers Exemplified by Natural Rubber

Abstract In the previous work of Kargin and Slonimskii and that of Kargin and Sogolov who studied the behavior of polymers over a wide range of temperature, it was shown that the shape of thermomechanical curves depends on magnitude of molecular weight of the polymers. As a result of investigation of theory and actual experimental studies in which polyisobutylene was employed, it was demonstrated that molecular weight could be estimated on the basis of thermomechanical properties. This suggested a relationship between the magnitude of molecular weight M found from the thermomechanical curves and that which was determined from glass temperatures Tg and fluid temperatures Tf. For practical use of this relationship, it is necessary to know the magnitude of the segments and two empirical constants. These values can be found by calculation of molecular weights of three different fractions of the polymer. This can be accomplished experimentally by any independent method. Once these magnitudes are determined, it is necessary to find, by means of the thermomechanical curve, the values Tg and Tf, in order to calculate the molecular weight of any sample of the same polymer. Because of the low degree of accuracy of determination of these values, and because of the peculiar differences, the reliability of the calculated molecular weight cannot be great, especially since the equation utilizes the logarithm of the molecular weight figure and not the molecular weight itself. Apparently the graphic solution is simpler than analytical methods: by means of the data of thermomechanical studies for various fractions of known molecular weights it is possible to graph the dependence of M or log Mon Tf−Tg. From what has been said, it is evident that we may use the demonstrated method only for polymers of high elasticity, and furthermore, only for those fractions in which Tf−Tg is greater than zero.