Ranjit S. Konar's research while affiliated with Indian Association for the Cultivation of Science and other places

Zusammenfassung Die von Montmorillonit und Kaolinit aus einer neutralen Phosphatlösung gebundene und nach Waschen mit dest. Wasser übrigbleibende P-Menge ist bei Anwendung des radioaktiven Isotops32P als Funktion der Art der austauschbaren Kationen gemessen. In beiden Mineral-Phosphat-Verbindungen stieg der P-Gehalt in folgender Reihe der untersuchten Kationen: K+∼ Mg++ ++ +++ +++. Bei Anwesenheit stark hydrolysierbarer, austauschfähiger Kationen, wie z. B. Al+++ und Fe+++, ist das Wasserauswaschen nur von den eigentlich überschüssigen Phosphationen fast unmöglich, weil adsorbierte Phosphationen teilweise durch Hydrolyse freigesetzt werden. Wasserausgewaschene, suspendierte Mineral-Phosphat-Verbindungen wurden mit Anionenaustauschern, R'(Am−), verschiedener Ionenartbeladung geschüttelt und der übrigbleibende P-Gehalt gemessen. Wenn Am− mit den phosphatbindenden, austauschbaren Kationen eine schwerlösliche Verbindung bilden, z. B. OH− und Al+++ bzw. Fe+++, erfolgt eine verhältnismäßig große Entfernung von Phosphationen von dem Mineral. Adsorptiv gebundene Phosphationen scheinen von R'(Am−) in größeren Mengen entfernt zu werden, je größere Ladung und Polarisierbarkeit Am− haben.

The kinetics of the aqueous polymerization of acrylonitrile initiated by the permanganate–oxalic acid redox pair have been studied gravimetrically at 32 ± 0.2°C. The rate of polymerization is independent of oxalic acid concentration over a small range. The catalyst exponent varies continuously with the catalyst concentration, being 0.9 at low catalyst concentration and 0.27 at high catalyst concentration at a monomer concentration of 0.30M. The monomer exponent is nearly unity in the concentration range 0.30M and above. The molecular weight of the polymer is independent of oxalic acid concentration in the range where the rate of polymerization is independent of the oxalic acid concentration but decreases at higher concentration of oxalic acid with increasing concentration of catalyst and temperature. The overall activation energy was found to be 8.6 kcal./mole. Addition of salts such as Na2SO4 depresses the rate of polymerization, but the addition of MnSO4 at low concentrations increases the rate, whereas at higher concentration the initial rate falls. It has been suggested that hydrated Mn3+ ions cause oxidative chain termination of polyacrylonitrile radicals. Complexing agents, such as fluoride ions, ethylene-diaminetetraacetic acid, etc., decrease the rate of polymerization, whereas addition of detergents enhances it.

The effect of organic solvents on the rate of heterogeneous aqueous polymerization initiated by the K2S2O8Na2S2O4 redox pair has been studied. The separating polymer phase remains in colloidal dispersion, the stability of which is partly due to charge and partly due to hydration. Both the water-miscible and water-immiscible organic liquids decrease the rate of polymerization, the limiting conversion, and the molecular weight of the polymers. It has been suggested that the water-miscible organic liquids preferentially solvate the latex particles and thereby decrease the hydration stability and monomer concentration in the latex particles, whereas the water-immiscible organic liquids decrease the monomer concentration in the latex particles due to the partition of the monomer between the aqueous and the nonaqueous phases. Thus the fall in the rate and molecular weight of the polymers may be ascribed to the increase in the termination rate by the faster coagulation of the latex particles and dilution of monomer concentration at the reaction site.

The effect of organic liquids on the rate of heterogeneous aqueous polymerization initiated by the KMnO4H2C2O4 redox pair has been studied. The separating polymer phase is a precipitate under experimental conditions. The rate of polymerization, the limiting yield, and the molecular weight of the polymers were found to decrease in presence of organic liquids. This behavior has been ascribed to (1) the increase in the termination rate due to the swelling of the precipitated polymer particles containing trapped radicals and (2) the fall in the monomer concentration at the reaction site.

The rate of polymerization of aqueous methyl methacrylate under nitrogen at 32°C. is proportional to the first power of catalyst (MnO4−) concentration (0.633 to 15.83 × 10−5 mole/l.) at fixed concentrations of the activator (0.8 × 10−2 mole/l.) and monomer (6.204 × 10−2 mole/l.), independent of activator concentration over a wide range (0.50 to 0.0625 × 10−2 mole/l.), and proportional to the first power of monomer concentration within the range (0.94 to 7.52 × 10−2 mole/l.) at fixed concentrations of the catalyst (3.16 × 10−6 mole/l.) and the activator (0.8 × 10−2 mole/l.). The initial rate of polymerization attains a maximum value at 45°C., but falls with further rise in temperature. The rate of polymerisation is depressed by agitation after initiation, salts and organic solvents, and is accelerated by MnSO4 and complexing agent like NaF (only at low monomer concentration), and in presence of peptizers like sodium cetyl sulfate or cetyltrimethylammonium bromide. The separating phase in the absence of peptizers is a course coagulum, and possibly a steady state with respect to radicals is not attained at high catalyst concentration. Injection of catalyst late in a run increases both the rate of polymerization and yield in unpeptized systems and does the reverse in peptized systems. The molecular weight of the polymers increases in the course of a run and is also affected by change of catalyst concentration but not by activator concentration in the range where the rate of polymerization is independent of activator concentration.

Polymerization of aqueous methyl methacrylate solution by oxalic acid (4.0 × 10−2 to 0.0625 × 10−2 mole/l.) and permanganate (0.633 × 10−5 to 63.3 × 10−5 mole/l.) system as redox initiator has been studied. Oxalic acid by itself can not initiate polymerization in the dark but does so strongly even in diffuse light or weak illumination. Permanganate can initiate polymerization provided the solution is sufficiently acidic to dissolve the separated colloidal MnO2 which tends to inhibit polymerization. The MnO4−-oxalic acid system is a powerful redox initiator provided the acid strength (either of added H2SO4 or of oxalic acid itself) is sufficient to dissolve MnO2. The polymer always separates as a coarse coagulum (suspension). The polymers have been examined for endgroups by the dye test as developed in this laboratory. Oxalic acid-initiated (in sunlight) as also oxalic acid—ferrous ion-initiated and KMnO4—H2C2O4-initiated polymers contain carboxyl endgroups. MnO2—H2SO4 acid-initiated polymers, have been found to contain sulfate endgroups. On increasing the ratio of oxalic acid to permanganate, the carboxyl endgroups tend to decrease, and ultimately very faint test for carboxyl is obtained. This is in agreement with the suggestion made by previous workers that under such conditions carboxyl radical-producing reactions are suppressed.

Carboxyl groups or endgroups have been introduced into polymers by use of the following four general methods: (1) use of a carboxyl-bearing initiator, (2) copolymerization with a carboxyl-bearing monomer, (3) chain transfer with a molecule containing an actual or potential COOH group, and (4) transformation of a reactive group already present in the polymer. The presence of the carboxyl endgroup in the polymer has been tested for a new technique called the “dye partition test,” developed in this laboratory. It has been demonstrated that all these methods can be used successfully to incorporate COOH groups in the polymer. Of particular interest is the fact that the incorporation of solvent fragments in polymers by chain transfer can be demonstrated very simply and conveniently by this method.