Showing papers by "Indian Association for the Cultivation of Science published in 1969"

Vinyl polymerization with Fe(III)-thiourea as initiator system. Part I. General features and kinetics of Fe(ClO4)3-thiourea reaction†

Abstract: Initiation of polymerization of methyl methacrylate, styrene, and acrylonitrile with the redox system Fe(III)—thiourea has been examined. For the heterophase polymerization any of the ferric salts, such as FeCl3, Fe2(SO4)3, and Fe(ClO4)3 can be used as oxidant, but there is no polymerization in the homogeneous phase when FeCl3 is used as oxidant. It was also observed that Fe(ClO4)3 retards the radical polymerization of styrene, though this salt has hardly any effect on the radical polymerization of methyl methacrylate. Further, the reaction between Fe(ClO4)3 and thiourea was found to be kinetically of second order. The rate is largely influenced by the nature of the solvent. It is concluded that apart from the dielectric constant of the solvents, specific effects like complex formation of Fe(III) with solvents should have a marked influence on the rate of this reaction.

Studies on the polymerization of ethyl acrylate. II. Chain transfer studies

Abstract: Transfer constants for different solvents representing hydrocarbons, halogenated compounds, alcohols, ketones, acids, and esters were determined in the thermal polymerization of ethyl acrylate at 80°C and they are compared with the available data on methyl acrylate and ethyl methacrylate. It was observed from the values of transfer constants that ethyl acrylate radicals are a little more effective than methyl acrylate or ethyl methacrylate in abstracting hydrogen atom from hydrocarbons and alcohols. In acetic and n-butyric acid media, it has been found, by the aid of endgroup analysis, that the derived solvent radicals from transfer reactions are not too efficient to start a new chain.

Penultimate unit effect in the copolymerization of alkyl methacrylates and styrene

Abstract: Kinetics of bulk copolymerization of styrene and alkyl methacrylates, namely, ethyl, isobutyl and n-nonyl methacrylate have been investigated at 60°C, and the extent of diffusion-controlled termination in these systems has also been checked. Rate-composition curves reveal that addition of a small amount of styrene in pure alkyl methacrylates markedly reduces the rate of polymerization, the effect becoming more important as the chain length of the ester group is increased. With higher alkyl methacrylates, the position of the minima in the curves shifts towards a lower concentration of styrene in the feed. The applicability of ARLMAN'S theory on the variation of the Φ-factor with monomer feed composition has been examined. Die Kinetik der Coplymerisation in Substanz von Styrol mit Athyl-, Isobutyl- und n-Nonylmethacrylat und das Ausmas des diffusionskontrollierten Abbruchs in diesen Systemen wurden bei 60°C untersucht. Aus den Kurven fur die Abhangigkeit der Polymerisationsgeschwindigkeit von der Zusammensetzung des Polymerisationsansatzes ergibt sich, das kleine Mengen von Styrol in reinem Alkylmethacrylat die Polymerisationsgeschwindigkeit verkleinern. Der Effekt wird groser mit wachsender Lange der Estergruppe; die Minima der Kurven verschieben sich zu kleineren Styrolkonzentrationen im Ansatz. Die Anwendbarkeit der Theorie von ARLMAN auf die anderung des Φ-Faktors mit der Monomerzusammensetzung wurde gepruft.

Ferrous-bromate redox as initiator of aqueous vinyl polymerization

Abstract: Ferrous-bromate redox is a very efficient initiator for the aqueous polymerization of a number of vinyl monomers. With methylmethacrylate, polymerization takes place in dark and at temperatures starting from 0 °C onwards. Bromate, ferrous and monomer exponents are respectively 0.51, 0.43 and 1.32 and the overall activation energy is 7.47 Kcal/mole. Neutral salts depress the polymerization rate, while an emulsifier increases it. pH of the medium has not much influence on the polymerization rate upto the value of 2.32. However, at pH 1.39, rate is somewhat depressed. Endgroups incorporated are hydroxyl and bromine totalling to an average of one per chain. Based upon these findings suitable mechanisms of initiation and termination have been proposed.

Grafting acrylic acid monomer to poly‐(vinyl alcohol) and methyl cellulose by ceric ion

Abstract: A graft copolymer of acrylic acid on poly(vinyl alcohol) was prepared by use of the ceric ion–polyol redox system in aqueous medium. The graft copolymer obtained was water-soluble under the specified experimental conditions. The efficiency of grafting was determined by measuring carboxyl group content (as expected from acrylic acid unit) in the copolymer by applying the newly developed reverse dye-partition technique. The graft copolymer was also characterized by viscosity and solubility measurements. The effect of varying concentration of catalyst, monomer, and grafting time has also been determined.

Unperturbed dimension of polystyrene from viscosity measurements in cosolvent media

Abstract: The method proposed by DEB and CHATTERJEE1 for the determination of unperturbed dimension of a polymer from solution viscosity data in different solvents and molecular weight has been applied to four fractions of polystyrene in a series of cosolvents consisting of varying amounts of acetone and cyclohexane. The solubility characteristics of these cosolvents, particularly the optimum solvent composition, have been examined with respect to the thermodynamic theory of R. L. SCOTT. Die von DEB und CHATTERJEE1 vorgeschlagene Methode zur Bestimmung der ungestorten Dimension eines Polymeren aus der Losungsviskositat in verschiedenen Losungsmitteln und dem Molekulargewicht wurde angewandt auf vier Fraktionen von Polystyrol in Losungsmittelgemischen aus Aceton und Cyclohexan in wechselnden Mengenverhaltnissen. Die Loslichkeitseigenschaften dieser Gemische, insbesondere die optimale Losungsmittelzusammensetzung, wurden im Hinblick auf die thermodynamische Theorie von R. L. SCOTT untersucht.

Dye‐sensitized photopolymerization of methylmethacrylate in nonaqueous media

Abstract: The dye-sensitized photopolymerization of methylmethacrylate by visible light in nonaqueous media especially benzene has been investigated using long chain aliphatic amines as activators For the typical system, eosin/cetyl dimethylamine/methylmethacrylate in benzene, the rate of polymerization has a square root dependence on light intensity and direct proportionality on monomer concentration, while with respect to eosin and cetyl dimethylamine, it passes through a maximum, indicating their dual role as both initiator and retarder The molecular weight decreases with increase in light intensity and eosin concentration, and also with decrease in monomer concentration However, the molecular weight passes through a maximum with cetyl dimethylamine concentration Electrondonating groups attached to the benzene nucleus in the halogenated fluorescein dye stuffs accentuate the sensitizing action of dye stuffs, while electron-withdrawing groups deactivate it The greater the chain length and the greater the amount of N-substitution in the long chain aliphatic amines, the greater is the activating influence The effect of combination of dye stuffs as well as the effect of solvents on the rate of polymerization are also discussed With increase in amine concentration, the average number of amino end groups per chain is reduced The presence of hydroxyl end groups has also been demonstrated in systems containing alcohols Presence of oxygen or air in the polymerization systems is always accompanied by an inhibition period and reduction in rate of polymerization The overall activation energy has been found to be 20 kcal/mole For the effect of different variables on the rate of polymerization and molecular weight tentative mechanisms following a free radical course have been suggested Die durch Farbstoffe fur sichtbares Licht sensibilisierte Photopolymerisation von Methylmethacrylat wurde in nichtwasrigen Losungen (in Substanz oder in Benzol) untersucht Fur die Reaktion sind langkettige aliphatische Amine als Aktivatoren notig Das typische System Methylmethacrylat/Eosin/Cetyldimethylamin/Benzol ist durch folgende Merkmale gekennzeichnet: Die Reaktionsgeschwindigkeit ist der Wurzel aus der Lichtintensitat einerseits und der Monomerkonzentration anderseits proportional, wahrend sie bezuglich der Konzentration des Eosins bzw des Amins durch ein Maximum geht; dies deutet auf deren Doppelnatur als Initiator und als Retarder Die Molekulargewichte fallen mit zunehmender Lichtintensitat bzw Eosinkonzentration und mit abnehmender Monomerkonzentration; bezuglich der Aminkonzentration gehen sie durch ein Maximum Die Bruttoaktivierungsenergie betragt 20 kcal/mol Halogenierte Fluoreszeinfarbstoffe mit Elektronendonator-Substituenten im Benzolkern zeigen eine verstarkte, solche mit Elektronenacceptor-Substituenten eine veinderte Sensibilisatorwirkung Fur die Amine gilt, das sie um so starker aktivieren, je langer die Kette ist und je mehr das N-Atom substituiert ist Die Wirkung von Farbstoff-Kombinationen auf die Reaktionsgeschwindigkeit und der Einflus verschiedener Losungsmittel werden diskutiert

Retardation of free radical polymerization by redox dyes. Effect of 2.6‐dichlorophenol indophenol in the polymerization of methyl methacrylate and styrene

Abstract: 2.6-Dichlorophenol indophenol, a redox dye, in its dissociated as well as undissociated form has been found to be a powerful retarder for the free radical polymerization of methyl methacrylate and styrene. The rate constants for the reaction of the dye with polymethyl methacrylate and polystyrene radicals are respectively 8 200 and 17 700 1. · mole−1sec−1 at 60°C. It has been found that for every dye molecule consumed the number of polymer radicals removed from the system lies between 1 and 2. Der Redoxfarbstoff 2.6-Dichlorphenolindophenol ist sowohl in seiner dissoziierten als auch in der undissoziierten Form ein wirksamer Retarder fur die radikalische Polymerisation von Methylmethacrylat und Styrol. Die Geschwindigkeitskonstanten der Reaktion des Farbstoffes mit den Makroradikalen haben bei 60°C die Werte 8200 (Methylmethacrylat) und 17 700 l · mol−1sec−1 (Styrol). Die Zahl der Makroradikale, die fur je ein verbrauchtes Farbstoffmolekul desaktiviert werden, liegt zwischen 1 und 2.

Studies on addition polymerization in mixed solvent system. Part IV. Chain transfer of glycols in the polymerization of styrene

Abstract: The behaviour of different glycols in the solution polymerization of styrene and their effect on the chain transfer step has been studied. The polymerization has been carried out in the homogeneous phase using mixed solvent systems at temperatures of 60, 80, and 100°C. On addition of glycols, the degree of polymerization decreased due to chain transfer and dilution, but when a certain concentration is reached, it gradually increased with increasing glycol concentration. This increase in the degree of polymerization has been attributed to the reduced termination rate resulting from a coiling of the growing polymer chain at higher glycol concentrations. The transfer constants of glycols have been observed to increase with the size of the alkyl groups. Consequently, the chain transfer reaction most probably takes place through the abstraction of H atoms from the alkyl group and not from the OH group of the glycols. Das Verhalten verschiedener Glykole bei der Losungspolymerisation von Styrol und ihre Wirkung auf die Kettenubertragung wurden untersucht. Diese Polymerisation wurde in Losungsmittelgemischen in homogener Phase bei 60, 80 und 100°C ausgefuhrt. Der Polymerisationsgrad wird als Folge der Kettenubertragung und der Verdunnung herabgesetzt, steigt jedoch von einer bestimmten Konzentration an mit steigender Glykolkonzentration an. Dieses Ansteigen des Polymerisationsgrades wurde der verminderten Abbruchgeschwindigkeit zugeschrieben, die von der Knauelbildung der wachsenden Polymerkette bei hoheren Glykolkonzentrationen herruhrt. Die Kettenubertragungskonstanten der Glykole steigen mit der Lange der Alkylgruppen an. Dieses deutet darauf hin, das die Kettenubertragung wahrscheinlich durch die Abspaltung eines Wasserstoffatoms der Alkylgruppe und nicht der OH-Gruppe der Glykole erfolgt.

On the spur of the product of Dirac matrices

Abstract: In this paper several methods for the evaluation of the spur of the product ofγ 5 matrix and any number of Dirac matrices have been established. The formulae for the determination of the various types of products of two spurs whenγ y ,γ i γ j ,γ i γ j γ k ,γ i γ j γ k γ l and these terms associated withγ 5 matrix occur in both of the spurs, have been derived. It has been shown that the product of two spurs each involvingγ 5 matrix, can be equated to an expression involving noγ 5 matrix. One useful identity for spurs involvingγ 5 matrix has been deduced.

Studies on addition polymerization in mixed solvent system. Part III. Chain transfer of glycols in the polymerization of methyl methacrylate

Abstract: The role of different glycols for the overall kinetics and particularly for the chain transfer step in the addition polymerization of methyl methacrylate has been studied. The polymerization of methyl methacrylate has been carried out in the homogeneous phase using mixed solvent systems at 60 and 80°C. The degree of polymerization has been found to decrease owing to chain transfer and dilution but after a certain concentration, it gradually increased with increasing glycol concentration. This increase in the degree of polymerization has been attributed to a reduced termination rate resulting from the coiling of the growing polymer chain at higher glycol concentrations. The chain transfer constants of glycols have been found to increase with the size of the alkyl groups indicating thereby that the chain transfer probably occurs via the abstraction of an H atom from the alkyl group and not from the OH group of the glycols. Der Einflus verschiedener Glykole auf die Kinetik und besonders auf die Kettenubertragung bei der Additionspolymerisation von Methylmethacrylat wurde untersucht. Die Polymerisation von Methylmethacrylat wurde in Losungsmittelgemischen in homogener Phase bei 60 bis 80°C ausgefuhrt. Der Polymerisationsgrad wird als Folge der Kettenubertragung und der Verdunnung herabgesetzt, jedoch steigt er von einer bestimmten Konzentration an mit steigender Glykolkonzentration an. Dieses Anwachsen des Polymerisationsgrades wurde der verminderten Abbruchgeschwindigkeit zugeschrieben, die von der Knauelbildung der wachsenden Polymerkette bei hoheren Glykolkonzentrationen herruhrt. Die Kettenubertragungskonstanten der Glykole steigen mit der Lange der Alkylgruppen. Dieses deutet darauf hin, das die Kettenubertragung wahrscheinlich durch die Abspaltung eines Wasserstoffatoms der Alkylgruppe und nicht der OH-Gruppe der Glykole erfolgt.

Chain-transfer constant of fluoroalcohols

Abstract: Chain transfer constants of some fluoroalcohols [HCF2(CF2)n−1CH2OH, n = 2, 4, 6] in the catalyzed polymerization of vinyl acetate, styrene, acrylonitrile, and methyl methacrylate at 60°C have been evaluated by a method based on degree of polymerization. Since fluoroalcohols are normally nonsolvents for polymers, a homogeneous reaction phase is maintained by carrying out the polymerization in benzene (except in case of acrylonitrile, where no solvent was used). The transfer constants vary, depending on the reactivity as well as the polarity of the radicals, in the following order: vinyl acetate > styrene > methyl methacrylate > acrylonitrile. Of the three fluoroalcohols studied, the transfer constants increase with the increasing value of n. The results have been interpreted in terms of polar structure contribution in the transition state of the transfer reactions.