Wiley

Spectra of methyl methacrylate polymers in chloroform solution at 90° show three α‐methyl proton peaks. Measurements of their areas in spectra of polymers prepared with free radical and anionic initiators indicate that these may be attributed to (1) isotactic sequences (ddd or lll), (2) syndiotactic sequences (ldl or dld), and (3) heterotactic sequences (ldd, dll, ddl, or lld). The conformation and stereochemical configuration of the chains may thus be examined with considerable discrimination; degrees of regularity, block sizes, etc. appear to be determinable. Free radical polymers of methyl methacrylate are found to be predominantly syndiotactic, whereas those produced with anionic initiators. such as n‐butyllithium, are shown to be predominantly isotactic, in agreement with the findings of others. The backbone methylene resonance also shows striking changes with chain stereochemical configuration, such as to provide absolute, independent confirmation of the assigned structures.

Expressions are derived from free volume considerations which predict the concentration dependence of viscosity and glass temperature for polymer‐diluent systems. Experimental data for several systems were examined and general agreement with theory was found over broad ranges of concentration. Particular emphasis is placed on the limited amount of information required for the application of these expressions to describe the viscous properties of polymer‐diluent systems.

Potentiometric titrations of polymethacrylic acid were performed at different concentrations, different molecular weights, and in the presence of neutral salts, as well as in dioxane‐water mixtures. It was shown that the pH of the solutions fulfills the relation, pH = pK — n log [(1 — α)/α]. pK and n are independent of the molecular weight and concentration if a suitable activity factor is introduced. The equation is applicable to free acid solutions as well as acid mixtures. Copolymers of the type, polyallyl acetate‐maleic acid, show a more complicated curve. The curve is of the “polydibasic” type. Each branch of it fits equation (2) well. The formula is analyzed and is proposed to be the result of the action of the Maxwell‐Partington statistical factor, as well as of the decrease in entropy accompanying the stretch of the randomly kinked molecule. This stretch is caused by the repulsive forces between the ionized carboxyl groups. The distribution curves of the various degrees of ionization present, for any pH, are given. The activity correction implies small units of the size of one or two carboxyl groups. The behavior in salt solutions is dependent not only on the activity correction, but also on the salting‐out factor. This factor is high in polyvalent salts. The titration curves in dioxane‐water mixtures are satisfactorily accounted for by the change in the activity factor with the dielectric constant.

The Gordon‐Taylor equation relating the glass transition temperature θ of a copolymer to the glass transition temperatures θ₁ and θ₂ of the homopolymers is equivalent to where c₁ and c₂ are the weight fractions of the constituents and A₁ and A₂ are constants. It can be recast into the following forms suitable for linear plots and where k = A₂/A₁. Data from the literature on 10 copolymer systems, including butaciene‐styrene copolymers, give linear plots, verifying the equation within experimental error. However, the observed value of k is in most cases significantly smaller than the ratio of the differences of the volume‐temperature coefficients for each homopolymer in the rubbery and glassy states, as required by the derivation of Gordon and Taylor. The glass transition temperature (in °C.) for a butadiene‐styrene copolymer prepared by emulsion polymerization at 50°C. may be calculated from the weight fraction c₂ of bound styrene as and for a similar 5° copolymer as

The infrared spectra of oriented films of valonia cellulose and of ramie and bacterial cellulose crystallites have been observed in the 3 μ region. Polarization properties of the bands have also been determined. The differences between the polarized spectra of bacterial and ramie crystallites in this region are attributed to per cent crystallinity and orientation effects. Two new bands in the CH stretching region have been observed. With this new information the CH₂ symmetric and antlisymmetric stretching modes are assigned to parallel and perpendicular bands, respectively, requiring a specific orientation of the CH₂OH group. From the observed polarization of the bands in the OH stretching region, a system of hydrogen bonding in the crystal structure of cellulose I is proposed. This involves a change in conformation of the cellobiose unit to permit an intramolecular hydrogen bond between the C₃ hydroxyl and the ring oxygen of contiguous glucose units. Two sets of intermolecular hydrogen bonds are proposed: in the 101 plane the C₆ hydroxyls of the antiparallel chains are joined to the bridge oxygens of the adjacent parallel chains; in the 101 plane the C₆ hydroxyls of the parallel chains are hydrogen‐bonded to the bridge oxygens of the adjacent antiparallel chains.

A general discussion about the method of colloid titrations is given in this report. A new titration method is based on the stoichiometric combination of positive and negative colloid ions. The end point is decided by indicators (known as metachromatic coloring matters) like toluidine blue. The standard colloid reagents are P.V.S.‐K (potassium salt of polyvinyl alcohol sulfate) and Macramin (N‐polymethylated chitosan derivatives). The typical operations of this method are described briefly: the direct, indirect, and differential titration methods. The colloid titration curve is somewhat different from the acid‐base titration curve obtained potentiometrically, but it is characteristic and reproducible under definite conditions and so it is useful in quantitative and qualitative analysis. This titration may be carried out even under extraordinary dilute conditions (5 × 10⁻⁴ N) and the entire process is quite similar to the usual acid‐alkali titration. The precision is below ±ca. 5% if the method is carefully followed.

The configuration of a poly‐L‐glutamic acid sample of 34,000 molecular weight has been studied in 0.2 M NaCl‐dioxane (2:1) as a function of pH and temperature by intrinsic viscosity, optical rotation, optical rotatory dispersion and infrared spectroscopy. The intrinsic viscosity and specific rotation fall sharply in the pH range of 5.4–6.4 reaching values that remain constant at higher pH. The indications that these changes correspond to a reversible helix‐random coil transition are substantiated by the demonstration that the optical rotatory dispersion shifts from the type characteristic of helices to the normal type as the pH is increased through the same region. Further evidence of the transition is found in infrared spectroscopic studies in solutions in which D₂O has replaced H₂O. The temperature dependence of the specific rotation and infrared spectra shows that within the pH region of 5.4 to 6.4 the equilibrium is shifted toward the coiled configuration by an increase in temperature. The analogy of this behavior with protein denaturation is obvious. It is noted that the transition from the helix to the coil does not begin until about 40% of the residues have become charged. The implications of the ability of the helical configuration to withstand this degree of electrostatic repulsion within its side groups is discussed in relation to the configuration of proteins.