Index of content:
Volume 12, Issue 6, 01 June 1944
12(1944); http://dx.doi.org/10.1063/1.1723934View Description Hide Description
The mechanism of catalytic copolymerization of two monomers A and B is treated with the the aid of steady state approximation. Two initiation and two termination rates are assumed, one for each monomer. Four propagation rates are considered, corresponding to the four possibilities of addition, namely, addition of monomer A to a chain ending in A * or to a chain ending in B * and addition of monomer B to a chain ending in A * or to a chain ending in B *. Over‐all rate and number average molecular weight are calculated. The composition of the polymer and the number distribution curves of groups of submolecules a and of submolecules b are calculated as functions of the monomer composition and two rate constant ratios. These last results are of general character and independent of the nature of the initiation and termination processes provided that the average degree of polymerization is ``high.''
12(1944); http://dx.doi.org/10.1063/1.1723935View Description Hide Description
A table of line strengths for rigid asymmetric rotors is given, by means of which to this approximation the relative intensities of all important rotational lines up to J < 13 for all bands of any molecule can be readily calculated, provided the asymmetry is roughly the same in the initial and final states. A classification of the irregularly spaced lines of the asymmetric rotor is made into ``sub‐branches'' defined by the changes of the K values of the initial level in the limiting prolate and oblate symmetric rotors, and into ``wings'' which collect together lines of the sub‐branches which have uniformly varying strength and Boltzmann factor, and fairly uniform spacing.
12(1944); http://dx.doi.org/10.1063/1.1723936View Description Hide Description
A number of colloid materials—proteins, plastics, and the like—have been coated in sheet form and ``fibered'' internally by stretching to 100 percent or more elongation. Circular disks were cut from the fibered sheets, and their degree of orientation measured in an (alternating) electric field. Account is given of the relation of the orientation measured to field strength, thickness, humidity, and moisture content. It was observed that induced electrical anisotropy is not shown by all kinds of natural and synthetic colloids; thus it is not shown by organophile xerogels, but only by the hydrophile ones. With most of these the electrical response depends upon the relative humidity and the absorbed water content, but with polyvinyl alcohol the effect was independent of the absorbed water.
12(1944); http://dx.doi.org/10.1063/1.1723937View Description Hide Description
Raman frequencies, relative intensities, and depolarization factors are reported for hexachloroethane and hexabromoethane. The relative intensities and depolarization factors were obtained by use of a Gaertner microdensitometer. The fundamental frequencies of hexachloroethane were used to calculate force constants from the equations used by Stitt for ethane. The Raman data indicate that the equilibrium configuration for hexachloroethane is that corresponding to the point group D 3d . The force constants so obtained were then used to calculate the values of the frequencies that are allowed by the selection rules in the infra‐red spectrum. Selection rules for the fundamentals, binary combinations, overtones of non‐degenerate frequencies, and overtones of degenerate frequencies up to the fourth overtone for any molecule whose symmetry is D 3h , D′3h , or D 3d were worked out and are discussed.
12(1944); http://dx.doi.org/10.1063/1.1723938View Description Hide Description
The kinetics of chain copolymerizations is developed for reactions consisting of three steps: first, an activation of stable monomer; second, a growth of activated polymer radical by means of monomer addition; third, a stabilization of the growing chains by (a) monomer addition, (b) by means of growing polymer [Eq. (1)]. The existence of a steady state in respect to the concentration of growing chains beyond the induction period is assumed. The rate constants of growth and termination will in general depend upon the individual composition and upon the nature of the activated chain end. Equations for the rate of change of mole ratio z of the two monomer species are developed in terms of mean rates of growth and termination obtained by averaging the actual rates over the distribution of growing polymer [(4), (4a), (4′)]. The equilibrium conditions lead to a set of difference equations for this distribution [(5), (5′)]. It is investigated whether the solution and results derived therefrom are of a form which permits a determination of the dependence of the rate constants for growth and termination upon the composition of the polymer molecule (6). In addition, the influence of the type of active chain end involved on over‐all rate and size distribution is considered by introducing four constants for propagation and termination, respectively, according to the four possibilities A — A, A — B, B — A, B — B [(6a), (7), (4b), (4b′)], but independent of chain composition. Various special cases according to the relative magnitude of the rates for the two reactants are presented. Experimentally it is difficult to distinguish on the basis of kinetic data between the foregoing mechanism and one in which the rates of growth (and termination) for each of the two kinds of monomer depend solely upon the nature of the monomer molecule added and are independent of the nature of the active chain end [(4c), (4c′), (4c″)]. Relations are derived for the molecular size distribution, the inhomogeneity of the copolymer mixture in regard to composition, the average molecular weight, and the average composition of copolymer as function of the composition of the monomer residue [(8a), (8a′), (9a), (10)]. The importance of these results for soluble and insoluble copolymers and for the theory of gel formation in vinyl‐divinyl type polymers is pointed out.
12(1944); http://dx.doi.org/10.1063/1.1723939View Description Hide Description
In dilute aqueous solutions the dye 1,1′‐diethyl‐2,2′‐cyanine chloride, a photographic sensitizer, has two broad molecular absorption bands with maxima at 4900 and 5230A. For a 10−2 molar watersolution at room temperature, which is a gel, a new, intense, and exceedingly narrow absorption and fluorescence band has been found at 5730A by G. Scheibe, and by E. Jelley by other methods. The electric polarization of this band in both absorption and fluorescence is parallel to the long dye polymers formed in the gel. In the present investigation the occurrence and behavior of this ``P band'' were studied for thin dye films deposited on glass from solutions containing water. The P band shifts about 50A to greater wave‐length, becomes broader and weaker, and finally disappears as the water is removed by pumping and/or by increasing the temperature. This behavior is reversible if water vapor is readmitted. The position of the P band enables a measurement of the humidity of the atmosphere surrounding the film. The effect of temperature from −195 to +100°C is described. The P band can be made to appear starting with watersolutions as dilute as 10−5 M by freezing the water, locally concentrating the solution. For dye films, there is observed a second, weaker absorption band (called the P M1 band) at 5430A similar to the P band in structure and behavior but polarized perpendicular to the polymer chains and requiring a higher dye concentration before appearing. Reasons discussed in the paper indicate that the P band is due to single dye polymer chains while the P M1 band should belong to a system of coupled chains lying mutually parallel and forming threads. These threads were observed microscopically. A dehydrated film may contain a fraction of the dye molecules in monomeric form, another fraction (showing only the molecular bands much broadened) in an array anchored to the supporting surface such that the mere addition of water vapor immediately produces the polymer chains with the P and P M1 bands, and the remainder in crystalline form with a broad absorption band at 5650 and a broad fluorescence band at 6200A. Experiments undertaken to determine the number of water molecules per dye molecule necessary for polymerization were only sufficient to determine that the order of magnitude of the ratio is from 1 : 2 to 10 : 1. An attempt is made to interpret the absorption and fluorescence bands of the polymer chains by the hypothesis of exciton migration.