Viscosity Behavior of Poly(2-Methoxycyanurate) of Bisphenol F and Bisphenol A

Abstract

Activation parameters of viscous flow of poly(2-methoxycyanurate) of bisphenol F and bisphenol A of different molecular weight fractions in chloroform and dioxane were calculated using the Frenkel-Eyring equation. Voluminosity of the polymer was also computed. From voluminosity data it is concluded that the polymer molecules are rigid spheres in the solvent systems studied.     

Characterization and Properties of Macromolecules. XII. Numerical Treatment of Gel Permeation Chromatography Data

Abstract

Gel permeation chromatography provides a continuous recording of polymer concentration as a function of elution time. The latter may be converted by appropriate calibration into molecular weight. The chromatogram may be analyzed numerically to yield the various molecular weight averages. This process involves a number of assumptions and approximations. The magnitude of the errors introduced in the calculated molecular weight averages by the methods described in the literature are reported.     

Characterization of Copolymers and Polymer Mixtures by Gel Permeation Chromatography

Abstract

Estimation of molecular weights from GPC data is complicated when the polymer sample consists of a mixture of homopolymers or of statistical copolymers with nonuniform compositions. This is because sizes of solvated polymer coils depend on solvent interaction with both the homo-and hetero-units of the copolymers and because the extent of solvation of different homopolymers can differ. The overall degree of solvation may change effectively with composition and use of a single “average” set of Mark-Houwink constants in calibration procedures will then produce false molecular weight data from the GPC data. A new molecular weight average, M _x, is defined to overcome this problem. This average can be determined from the GPC chromatogram and intrinsic viscosity of the sample in the GPC solvent. Mark-Houwink coefficients are not needed. M _x lies between M _w and M _z.     

Functional Characterization of Hydroxy-Polybutadienes

Abstract

Analysis of hydroxyl functionalized polymers requires accurate knowledge of both molecular weight and functionality distributions. Usual average characterization such as viscosity (Brookfield and hydroxyl equivalent of the whole polymer, are not sufficient to represent product quality. Size exclusion chromatography, even with dual detection, is also limited in its capacity to characterize this type of macromolecules consequently their mechanical behaviour. Separation according to functionally has been achieved using stepwise elution from silica gel. the various problems encountered during analysis and the data finally obtained on HTPB using infrared spectroscopy are discussed.     

A Modified Method for Estimating Unperturbed Dimensions of Macromolecules from Viscosity Data

Abstract

A new empirical equation is presented which modifies the Krigbaum equation for calculating Kθ values from measurements of intrinsic viscosity in good solvents. This is found to fit the molecular weight data better for the polymer systems investigated.     

An Eluent Pressure Detector for Aqueous Size Exclusion Chrohatography

Abstract

An on-line viscometer which measures the eluent pressure drop across a long capillary was developed for use in aqueous size exclusion chromatography (SEC). Intrinsic viscosities of several polymer standards were calculated from data collected by the viscometer. These viscosities agree well with the measurements made with a Ubbelohde four-bulb shear dilution viscometer. The on-line viscometer becomes more sensitive as polymer hydro-dynamic volume increases. Therefore, it can be more effective than a refractive index detector for SEC analysis of high molecular weight, water soluble polymers.     

Number-Average Molecular Weights from Viscosity Measurements during Random Degradation of Polymers

Abstract

Using the theories of random degradation of Montroll and Simha, relationships are derived among limiting viscosity number, degree of degradation, and number-average molecular weight for a polymer undergoing random degradation in a closed system. Relationships among these parameters are derived for initial distributions of the “coupling” and the monodisperse types. Computer programs have been written which rapidly provide reliable values of number-average molecular weights and degrees of degradation from measured viscosity data on polymers with these initial distributions undergoing random degradation.     

Multicomponent analysis of poly(propylene) using fractionation,tacticity and molecular weight data

Heterogeneous Ziegler-Natta catalysts are known to contain multiple catalytic sites and produce polymers that contain multiple components. An approach is described in this work that combines fractionation, ¹³C NMR and molecular weight distribution data to determine the number and the characteristics of the different components found in the polymer. The methodology is applied to published data on poly(propylene). The analyses indicate that poly(propylene) made with heterogeneous Ziegler-Natta catalysts consists of at least four components. Three of these components obey enantiomorphic-site models, and the fourth component obeys Bernoullian model.     

Bis(3,6-di-tert-butylcatecholato)tin(IV) ditetrahydrofuranate in radical polymerization of methyl methacrylate

The effect of bis(3,6-di-tert-butylcatecholato)tin(IV) ditetrahydrofuranate (1) on the kinetic parameters of methyl methacrylate polymerization and on the molecular weight characteristics of polymers prepared was studied. According to EPR data, complex 1 can accept and eliminate the growing macroradicals in monomer media. This allows the lifetimes of the growing polymer chains to be controlled. The optimal temperature range for accomplishing controlled synthesis of polymer in the presence of complex 1 was determined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1314–1319, July, 2007.     

A Thermal Decomposition and Glass Transition Temperature Study of Poly(p-chlorostyrene)

Abstract

The thermal decomposition and the glass transition temperature of poly(p-chlorostyrene) (PpCIS) were studied with a Model 2 differential scanning calorimeter (DSC). The undecom-posed and decomposed polymers were analyzed by gel permeation chromatography for molecular weight distributions and by DSC for changes in the polymer glass transition temperature. The decomposition of PpCIS under isothermal conditions during 50 min intervals at various temperatures or at a fixed temperature (320°C) but for different periods is characterized by the disappearance of increasing quantities of high molecular weight polymer and the appearance of low molecular weight products. Random scissions have been shown to break down the polymer chains which depolymerize into volatile products. Activation energy (72 kcal/mole) for the decomposition of PpCIS is lower than that (103 kcal/mole) for the decomposition of polystyrene.     

Functionality and Functionality Distribution Measurements of Binder Prepolymers

Abstract

The functionality of a prepolymer, which is defined as the ratio of molecular weight to equivalent weight, is probably the most important single parameter that determines the properties of the cross-linked polymer network. The determination of prepolymer functionality therefore requires accurate knowledge of both number average molecular weight and equivalent weight. Ideally, a suitable prepolymer for propellant binder applications has terminal functionality (OH or COOH). Such a prepolymer theoretically has a functionality of 2.0. Because of uncontrolled chain termination reactions during the prepolymer synthesis, however, not all polymer chains have the desired functional end group. As a result, prepolymers generally have a distribution of functionalities, including onfunctional, monofunctional, and the desired difunctional prepolymer.     

The Errors in the Treatment of Gel Permeation Chromatography Data: Origins and Corrections

Abstract

This paper deals with the origins of errors in data interpretation when using modern GPC with dual detection (refractometer-viscometer) as a method of determination of average molecular weights of polymers. We describe here the different errors classified in two groups: typical chromatographic errors and data treatment errors and we show that they can lead to very miscalculated molecular weight values. For every case, we have tried to propose the best way to avoid or correct these errors so as to use modern GPC as a very accurate method of polymer characterization.     

Synthesis of Star-Shaped Polymers via Coordination of Bipyridyl-Terminated Polyoxyethylene with Metal Ions

Abstract

This paper describes the synthesis of various star-shaped polymers by means of complexation of bipyridyl-terminated polyoxyethylene with Ru(II) ion. Three kinds of bipyridyl-terminated polyoxyethylenes of different molecular weights were prepared from the corresponding polyoxyethylene monomethyl ethers with narrow molecular weight distributions. Bipyridyl was found to be introduced quantitatively at the end of the polymers based on the results of UV spectra. The formation of a star-shaped polymer was carried out by the reaction of RuCl₃ with three equivalents of bipyridyl-terminated polyoxyethylene. The UV spectrum of the star-shaped polymer obtained supported the formation of a typical Ru(II) tris(bipyridyl) complex. From the results of GPC, the star-shaped polymer obtained had a higher molecular weight than the pre-polymer and showed a narrow molecular weight distribution. In the case of a Ni(II) or a Co(II) complex, however, the star-shaped polymer was found to be dissociated into three linear prepolymers under the conditions of GPC measurement.     

Polymerization of Dioxolane by Triethyloxonium Hexafluorophosphate

Abstract

The polymerization of dioxolane by triethyloxonium hexafluorophosphate in methylene chloride has been studied with a view to determine the nature of the active center. NMR studies of solutions of the initiator with low ratios of monomer led to little reaction of the initiator over long times. Analysis of normal reaction mixtures showed that only a small amount of the initiator was consumed during the reaction. The polymer was studied by GPC, UV spectroscopy, and NMR. The polymer appears to consist largely of high molecular weight material with M_w/M_n less than 2, and also low molecular weight material perhaps formed by a different mechanism. The high molecular weight material appears not to have been formed by a simple linear trialkyloxonium ion, from end-group studies, and it is suggested the active center is a secondary oxonium ion on a large cyclic polymer.     

Gel permeation chromatography of polyethylene: Effect of long-chain branching

The effect of long-chain branching on the size of low-density polyethylene molecules in solution is demonstrated through solution viscosity and molecular weight measurements on fractionated samples. These well-characterized fractions are analyzed by gel permeation chromatography (GPC), and it is shown that the separation of the polymer molecules by this technique is sensitive to the presence of long-chain branching. By using fractions of branched polyethylene possessing differing degrees of branching, one observes that a single curve is adequate in relating elution volume to molecular weight. This calibration curve is applied in the GPC analysis of a variety of commercial low-density polyethylene resins and it is shown, by comparison with independent osmometric and gradient elution chromatographic data, that realistic values for molecular weight and molecular weight distribution are obtained. The replacement of molecular weight M by the parameter [η]M as a function of elution volume, leads to a single relationship for both linear and branched polyethylenes. This indicates that GPC separation takes place according to the hydrodynamic volumes of the polymer molecules. The comparison of data for polyethylene and polystyrene fractions suggests that this volume dependence of the separation will be observed for other polymer–solvent systems.     

Concentration effects in gel-permeation chromatography

Peak elution volume in gel-permeation analysis of polymers depends on sample concentration as well as molecular weight. Elution volume is related to the logarithm of the hydrodynamic volume of the solvated polymer species. The hydrodynamic volume of a given species is, in turn, inversely related to the concentration. Since molecular weight and concentration are interacting variables, the elution volume–molecular weight relation is not uniquely determined. A model is presented which accounts quantitatively for concentration effects, using parameters which are available a priori. The data required are polymer molecular weight, concentration, and density and the Mark-Houwink relation for the particular polymer-solvent combination.     

A pH Effect in the HPSEC Separation of Polyacrylamide-Based Copolymers

Abstract

Four polyacrylamide-based samples, having the same nominal molecular weight and molecular weight distribution, have been characterized by HPSEC using two column sets and a mobile phase of phosphate buffer. Depending upon the pH, the separations demonstrate that the systematic differences between samples are influenced by the level of anionic sites along the polymer chain. It is found that the HPSEC elution profiles of these samples are reversed when the pH is changed from 2.2 to 7.0. The anionicity of the samples ranges from less than 0.5 mole % carboxyl content (the homopolymer of acrylamide) to 33.0 mole %.

Capillary viscometry data support these findings in the two solvent media, indicating that no adsorption effects prevail in the chromatography. Static and on-line low angle laser light scattering (LALLS) data on the homopolymer of acrylamide also suggest that no adsorption or degradation is occurring in the chromatographic process.     

Synthesis of Controlled Block and Graft Copopolymers. II. Block and Graft Polymerization Initiated by Monohalo-Containing Polymer/Manganese Carbonyl Systems

Abstract

Block polymerization of methyl methacrylate initiated with monohalo-terminated polystyrene/manganese carbonyl systems were investigated. The rate of polymerization was lower than that of the trihalo-terminated polystyrenelmanganese carbonyl system. The molecular weight of the block copolymers obtained was independent of the conversion. To define the polymerization mechanism, 1-bromobutane was employed as a model compound for monohalo-terminated polystyrene. Polymerization kinetics followed a modified rate equation based on the Michaelis-Menten mechanism. The molecular weight of the block co-polymer could be regulated by varying the ratio of monohalo-terminated polymer to methyl methacrylate. Graft polymerization of methyl methacrylate initiated with chloromethylstyrene-styrene copolymer/ manganese carbonyl was also carried out. The polymerization behavior was strongly affected by the concentration of manganese carbonyl. Characterization of graft copolymers by GPC and halogen analysis showed that the number of grafting points per backbone polymer molecule increased when the concentration of manganese carbonyl was raised, but that the branches became shorter.     

Size Exclusion Chromatography with Low Angle Laser Light Scattering Detection

Abstract

A review is given of the use of low angle laser light scattering (LALLS) detection in conjunction with size exclusion chromatography (SEC) to measure polymer molecular weight distributions without conventional SEC column calibration methods. A summary of light scattering theory is presented, and instrument configurations and principles of operation are described for two LALLS photometers. Also discussed are the overall performance of the SEC/LALLS technique and data from selected applications.     

Gamma Radiation-Induced Template Polymerization of Acrylic Acid in the Presence of Polyactrylamide

Abstract

Poly(acrylamide-acrylic acid) resin p(AM-AA) was prepared by gamma radiation-induced polymerization of acrylic acid in the presence of polyacrylamide as a template polymer. The polymerization was studied by a free radical mechanism at different experimental conditions such as: absorbed dose, monomer concentration, polymer/monomer molar ratio and the weight-average molecular weight or the swelling degree of added polymer. The resin was obtained at dose > 10 KGy and there is no significant change in the swelling degree of the resin. The results showed that the capacity of the resin increases by increasing the monomer concentration, the weight-average molecular weight of the added polymer and decreases by increasing polymer/monomer molar ratio and the swelling degree of the added polymer. It was also found that the capacity of the resin depends on the radiation dose.