Tibor Kelen

Analysis of the Linear Methods for Determining Copolymerization Reactivity Ratios. I. A New Improved Linear Graphic Method

Abstract A new graphically-evaluable linear method is suggested for the determination of the reactivity ratios of copolymerization. The proposed new equation is very well adaptable for visual determination of the applicability of the copolymer composition equation. If the experimental data are adequate to the composition equation, the procedure offers a simple and reliable method for the graphical determination of copolymerization constants.

Analysis of Linear Methods for Determining Copolymerization Reactivity Ratios. III. Linear Graphic Method for Evaluating Data Obtained at High Conversion Levels

Abstract If copolymerizations are carried to high conversions, the determination of copolymerization parameters involves significant computational difficulties because the exact integrated form of the copolymerization equation has to be applied. A simple method has been developed to transform experimental data, even at high conversions, to be used in the differential form of copolymerization equation. In this method an average monomer composition is assigned to the corresponding experimental average copolymer composition. The proposed approximation extends the use of our linearization technique previously developed for low conversions. It was established that this method yields highly reliable results for practically.

Confidence intervals for copolymerization reactivity ratios determined by the Kelen-Tds method

SummaryCalculation method of confidence intervals for copolymerization reactivity ratios determined by the linear Kelen-Tüdős method is described, both for low and high conversions. The intervals as well as the confidence regions were compared with those obtained using non-linear estimation. No considerable deviations were found either in the parameter values or in their errors.

Polymer-analogous reactions of polyenes in poly(vinylchloride)

ABSTRACT The primary process in the thermal degradation of PVC in an inert atmosphere and at relatively low temperatures, is the elimination of hydrogen chloride molecules and the formation of polyene sequences of different lengths. The polyenes formed are highly reactive and participate in different secondary reactions. It has been shown for PVC samples degraded both in dilute solution and in the solid state that the amount of polyenes does not correspond to the degree of dehydrochlorination: proportionality may be observed only at the initial stage of degradation and, later on, the number of double bonds in the system is much lower than the amount of hydrogen chloride molecules split off. With the increase of conversion the increase in the amount of polyenes containing three or more double bonds gradually slows down and, later on, practically ceases. This phenomenon is also quantitatively well interpretable by intramolecular cyclization (backbiting) of polyenes. The reaction leads to cyclohexadiene structures. On completing the kinetic treatment of the process, we determined the relative rate constant of cyclization. Reactive dienophilic reagents readily react with the polyenes formed in degraded PVC. Based on the changes observed in the u.v. and visible spectra, a kinetic study was made on the Diels–Alder reaction with chloromaleic anhydride. The kinetic treatment, performed on the basis of a presumed mechanism, allowed the determination of the rate constants and their temperature dependence. Depending on the experimental conditions, the polyenes formed in the course of degradation may participate in other reactions as well. Some of the possible reaction routes are: the change in molecular weight, the formation of low molecular weight aromatic compounds (e.g. benzene) and the considerable proton exchange observed in the reaction of polyenes with hydrochloric acid.

The reinitiation mechanism of HCl catalysis in PVC degradation

SummaryThe effect of HCl on the thermal degradation of PVC has been studied. Changes in UV and visible spectra and kinetics of HCl loss indicate that HCl is able to reinitiate the allyl-activated zip elimination by proton exchange with polyenes. Also polyene-consuming secondary reactions are accelerated by HCl.

Evaluation of high conversion copolymerization data by a linear graphical method

A method is presented by which experimental data for copolymerization can be treated also at high conversions to allow determination of copolymerization para meters by a simple, graphically evaluable linear equation.Compared to the usual experimental errors, the error of approximation is negligible up to 50% conversion and thus does not affect the reliability of the parameters determined.AbstractПриводится метод, с помощью которого экспериментальные данные по сополимеризации, включая также данные при высоких конверсиях, могут быть обработаны для определения параметров сополимериз ации с помощью простого, графически оцениваемого линейного уравнения.Сравнивая с сбычными ошибками измерений, погрешностью данного приближения можно пренебречь вплоть до конверсий 50%, что, т.о., не оказывает влияния на надежность параметров.

Reversible crosslinking during thermal degradation of PVC

SummaryPVC undergoes rapid crosslinking during thermal degradation. Diels-Alder addition of conjugated polyenes was proposed as a possible crosslinking mechanism by earlier authors. By the use of conditions favoring retro Diels-Alder reaction of crosslinks (treatment with maleic anhydride at elevated temperature) it was proved that crosslinks are largely reversible. Evidently Diels-Alder addition of the conjugated polyenes plays an important role in crosslinking during thermal degradation of PVC.

Study of the thermal oxidation of polyolefines—IX: Some differences in the oxidation of polyethylene and polypropylene

Abstract In the thermal oxidations of polyethylene (PE) and polypropylene (PP), both similarities and differences are found. In the initial stage, the ratio of the hydroperoxide formed and the amount of oxygen absorbed is independent of both the nature of the polymer and the actual reaction conditions. With increased conversion, however, this ratio decreases to a greater extent in the case of PE than for PP. Most of the carbonyl groups formed in the PE chain during oxidation are ketones and carboxyls, but in PP there are also carbonyls with different structure. The amount of carbonyl groups in PE is approximately 1.5 times that observed for PP. The number of scissions involving considerable molecular weight decrease is higher for PE than for PP: for identical conversions, the ratio of scissions is S PE / S PP ∼ 6.

Quasiliving Carbocationic Poiymerization. III. Quasiliving Polymerization of lsobutylene

Abstract The polymerization of isobutylene has been investigated by the use of the steady, slow, continuous monomer addition technique in the presence of a variety of initiating systems, i.e., “H2O”/TiCl4, “H2O”/AlCl3, C6H5C(CH3)2Cl/TiCl4, p-ClCH2 C6(CH3)4* CH2Cl/AlCl3 at -50°C. Quasiliving polymerizations have been obtained with the “H2O” and C6H5(CH3)2Cl/TiC14 systems in 60/40 v/v n-hexane/methylene chloride solvent mixtures with very slow monomer input. After a brief “flash” polymerization, the M n of PIB increased linearly with the cumulative amount of monomer added (consumed); however, the number of polymer molecules formed also increased, indicating the presence of chain transfer to monomer. With the “H2O”/TiCl4 initiating system, M n,max was 56,000 and M w /M n < 2.0. By the use of the C6H5C(CH3)2CL/TiCl4 initiating system, quasiliving polymerization has been achieved and chain transfer could virtually be eliminated.

Crosslinking, scission and benzene formation during PVC degradation under various conditions

SummaryThe kinetics and mechanism of crosslinking and chain scission has been studied on several PVC samples during thermal thermooxidative, dynamic, and HCl catalyzed degradation. During pure thermal degradation crosslinking at a constant rate without scission occurs, while in the presence of oxygen and/or shear scission is not negligible. In the dynamic test, under shear both processes are fast, compared to static tests. The mechanism of benzene formation without main chain scission is discussed.