Santi R. Palit

END-GROUP STUDIES USING DYE TECHNIQUES

Abstract The end group in a macromolecule is a birth and death record stamped on the molecule itself. Generally the end group differs in composition from the main chain and constitutes a minute fraction of the macromolecule. Its quantitative determination demands ultra sensitive methods and the results are highly significant from the viewpoint of both theoretical and practical interests. The theoretical interests include: 1. Knowledge of the transient free-radical intermediates participating in the initiation reaction in radical polymerization vis -i-vis the chemistry of free radicals. 2. Determination of the rate of initiation from the extent of in corporation of initiator fragment and rate of polymerization [1]. 3. Knowledge of the mode of termination reaction. 4. Determination of degree of polymerization (DP) when the mode of termination is known. 5. Elucidation of the chain-transfer process and the determination of the chain-transfer constant.

Studies in chain transfer V. Acrylonitrile

Chain-transfer coefficients (Cs) with twenty-six different solvents at 60° C for acrylonitrile (M) have been measured by catalyzed polymerization studies using azobisisobutyronitrile (I) as catalyst ([l]/[M] = 6.1 x 10-4 mol/l.). For non-halogenated solvents the Cs values are found to be generally higher by an order than those of styrene, but the relative trend is more or less similar in both cases. The transfer characteristics of acrylonitrile with halogenated solvents are, however, in striking contrast with those of all other monomers so far studied. The halogenated solvents such as CCl4 which are usually extremely high chain-transferring agents are found to be devoid of any special susceptibility to an attack by the free radical of acrylonitrile. It is suggested that the inherent instability of compounds containing the group of >C(Cl)CN is responsible for the above unusual behaviour. The CM and 8 (= k1/2t/kv) for acrylonitrile (60° C) have also been determined and are 2.6 x 10-5 and 2.8 respectively.

Solubilization of Water in Non-Polar Solvents by Cationic Detergents

Solubilization of water in common organic solvents by fatty acid salts of long-chain (C12—C18) aliphatic primary amines was studied. It was found that, of all the salts from formate to palmitate and oleate, dodecylamine-n-butyrate and octadecylamine propionate solubilize most in xylene, the figure reaching about 29 molecules of H2O /mole of soap. Additions of free amine enhanced solubilization, while free butyric acid decreased the intake. Our viscosity and freezing-point measurements of the same systems indicated that the additive is most likely to form a complex with soap micelles, and that their solubilizing power is modified thereby. Freezing-point measurements of detergent solutions with and without the solubilized phase showed, surprisingly enough, that the dissolved water elevates the freezing-points considerably, showing that solubilized water acts as a binding agent between micelles and probably promotes micelle formation. The results are discussed and correlated on Winsor’s theory of solubilization.

A direct volumetric method for the analysis of soap

SummaryGlycol, or preferably its mixture with a solvent for hydrocarbons, such as isopropyl alcohol or chloroform, possesses high solvent power for soaps, which may be directly titrated with strong acids, either potentiometrically or with the use of methyl red or methyl orange. The ionization of the organic acid is suppressed so that salts of weak acids can be directly titrated by this method. The colors of the indicators are brighter and the end-point sharper than those in alcohol or water.

Ferrous-bromate redox as initiator of aqueous vinyl polymerization

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.ZusammenfassungEisen-Bromat-Redox ist ein sehr wirksamer Initiator für Polymerisation in wäßriger Lösung einer Zahl von Vinyl-Monomeren. Mit Methylacrylat findet die Polymerisation im Dunklen statt, startend bei Temperaturen von 0 °C aufwärts. Bromat-Eisenoxyd-Monomeren-Exponenten sind 0.51, 0.43 und 1.32 und die mittleren Aktivierungsenergien sind 7.47 kcal/Mol. Neutrale Salze vermindern die Polymerisationsgeschwindigkeiten, während ein Emulgator sie erhöht. Das pH des Milieus hat nicht viel Einfluß auf die Polymerisationsgeschwindigkeiten bis zu Werten oberhalb 2.32. Bei pH 1.39 wird sie etwas herabgesetzt. Eingebaute Endgruppen sind Hydroxyl und Brom, insgesamt im ganzen eine pro Kette. Auf Grund dieser Ergebnisse läßt sich ein passender Mechanismus der Initiatierung und des Abbruchs vorschlagen.

Studies in chain transfer IV. Catalyzed polymerization of vinyl acetate

The chain-transfer coefficients, Cs = ks/kp of highly purified vinyl acetate for twenty-five solvents at 60° C using azobisisobutyronitrile as catalyst have been measured. The Cs values are in most cases higher by an order than that of styrene or methyl methacrylate, though the relative order is more or less the same with all the three monomers. This is in agreement with the view that the free radical preferentially attacks the a-hydrogen. The absolute values of the rate of chain transfer, ks of vinyl acetate are, however, found roughly about one thousand times higher for vinyl acetate in comparison with the other two monomers for most solvents. A chemical explanation based on the stability of the transferred atom in the typical compound of low molecular weight formed by transfer is found to be in agreement with known facts about vinyl acetate and other monomers. The behaviour of chlorinated solvents is found to be rather difficult to understand because of the simultaneous transfer of chlorine and hydrogen, but the general tendency of high transfer with higher chlorine: carbon ratio is maintained. The theoretical foundation of such measurements has been briefly discussed, and the possibility of obtaining Cs values by a single-tube experiment in suitable systems has been indicated.

The solubility of heavy metal soaps in co-solvent mixtures of chloroform and propylene glycol

SummaryThe solubilities of the myristates, laurates, palmitates, and stearates of magnesium, lead, calcium, barium, and zinc have been measured at 25° C. in chloroform and in propylene glycol and in their mixtures. Even where they are sparingly soluble in the solvents separately, they dissolve freely in mixtures of the two.For each metal the solubility is greatest for laurate and least for stearate and it is very low for zinc soaps, particularly zinc stearate.Heavy metal soaps may be directly titrated with acid in mixtures of propylene glycol and chloroform using thymol blue as indicator (yellow to pink).

Weak dipolar interaction in solutions: System: Benzene + chlorobenzene and toluene + chlorobenzene

Abstract In continuation of our earlier work, excess heats of mixing and volume changes of mixing have been measured for mixtures of chlorobenzene + toluene and chlorobenzene + benzene. The results have been analyzed both in the light of Balescus theory and our modified approach reported earlier. Analysis shows that our modified approach gives better agreement and the systems should be treated as a mixture of polarizable polar and polarizable non polar molecules.

Studies in chain transfer II. Catalyzed polymerization of methyl methacrylate

The chain-transfer reaction between growing methyl methacrylate (M) polymer radical and toluene (S) when catalyzed by varying quantities of benzoyl peroxide (B) at 80 and 60°C and p-nitrobenzoyl peroxide at 80°C has been studied. It has been established that the transfer constant calculated from the slope of 1/P̄ against S/M curve at constant B/M is not affected by the presence of low concentrations of benzoyl peroxide (B), which opens up the possibility of using catalysts for chain-transfer studies. At high concentrations of the catalyst, p-nitrobenzoyl peroxide, the calculated transfer constant has been found to be appreciably altered due to transfer with the catalyst itself. A crucial experimental test of whether the initiation mechanism is unimolecular or bimolecular has been made. In conformity with the deduction from the latter mechanism it has been found that at a constant monomer concentration 1/P̄ against √(B/M) plot is linear, and the slope of this line remains unaffected by a change of monomer concentration. On the contrary, the alternative deduction based on unimolecular initiation that 1/P̄ against √(B/M) plot should be linear and of equal slope at all monomer concentrations is found inconsistent with experimental data. This strongly supports bimolecular initiation and definitely discounts the idea of monomolecular initiation by the catalyst. Four probable mechanisms from literature which are equivalent to a bimolecular mechanism are discussed. A critical test of the whole scheme has been made by calculating D. P. values in bulk polymerization by extrapolation from our data in solution. These extrapolated values are used to construct 1/P̄ against √(B/M) curves, and these latter curves are compared with similar curves based on experimentally determined data. A fair degree of concordance between the predicted and the observed values, the predicted values being somewhat lower, is obtained, confirming the essential correctness of the assumed mechanisms of polymerization and chain transfer.

Electrochemical reduction and oxidation of nitrogen through low-current electrolysis

Dissolved nitrogen is reduced to ammonia at a platinum cathode enclosed in a cellophane membrane and is oxidised to nitric acid at a similarly enclosed anode at very low current density (∼1 mA/cm2), the electrolyte being distilled water. This is attributed to highly active reducing and oxidising species formed near the cathode and anode respectively under such low-current low-concentration condition of electrolysis.