C. Y. Liang

Infrared Spectra of High Polymers. II. Polyethylene

The infrared spectrum of polyethylene has been obtained between about 3000 cm—1 and 70 cm—1, polarization measurements on oriented specimens having been obtained to about 350 cm—1. Assignments of the fundamentals are made with the help of a group theory analysis. The assignment of the controversial CH2 wagging mode is discussed in detail and especially in terms of new evidence from the spectra of n‐paraffins, both as single crystals and as polycrystalline aggregates. It is shown that this mode is to be assigned to a weak band at 1369 cm—1. A satisfactory determination of the bands which arise from CH3 groups is also made possible by a study of the paraffin spectra. The splitting of bands in the spectrum is conclusively shown to arise from interactions between molecules in the crystalline phase. The nature of this interaction is discussed in terms of recent theories.

Infrared Spectra of High Polymers. III. Polytetrafluoroethylene and Polychlorotrifluoroethylene

The infrared spectra of polytetrafluoroethylene and polychlorotrifluoroethylene have been obtained between 4000 cm—1 and 70 cm—1. Polarization measurements on oriented samples were obtained in the region of 4000 cm—1 to 300 cm—1. It is known from x‐ray diffraction studies that both polymers have helical chain configurations. From a factor group analysis of the one‐dimensional space group, selection rules and approximate vibrational patterns of the infrared active fundamentals have been derived. A calculation of the normal frequencies of an assumed planar zig‐zag chain model of (CF2)n has been made, resulting in a satisfactory assignment of the bands in the infrared spectra of both polymers.

Infrared Spectra of High Polymers. I. Experimental Methods and General Theory

The problems involved in obtaining and interpreting the infrared spectra of high polymers are discussed. Experimental methods are described for recording the infrared spectrum, with particular emphasis on the techniques used in the region between 30 and 140 μ. The method for obtaining selection rules for high polymer spectra is described and the use of selection rules and other techniques for assigning fundamental frequencies is evaluated. The calculation of the skeletal frequencies of a polymer molecule is discussed in detail.

Infrared Spectra of High Polymers. VIII. Polyvinyl Nitrate

The infrared spectrum of polyvinyl nitrate has been obtained in the extended region of 70 to 3600 cm−1. Polarized infrared measurements were made on oriented specimens in the range of 350 to 3600 cm−1. Since x‐ray diffraction patterns indicate no crystallinity, the analysis has been based on an assumed atactic configuration. With the help of previous studies of high‐polymer spectra and results obtained on small molecules, it has been possible to make a complete assignment of all of the expected fundamentals. Dichroic measurements have not only permitted a decision on the assignment of the controversial NO2 rocking and bending modes, but suggest certain details concerning the local configuration of the nitrate group. There seems to be evidence that, although the specimen is not crystalline, a significant proportion of the chains have configurations not far from a planar zigzag chain.

Behavior of Gas Bubbles in Viscoelastic Materials in a Creep Process

This paper investigates the dynamic behavior of a spherical bubble situated in viscoelastic (or elasticoviscous) materials in a creep process. Both the diffusion of the dissolved gas in the material and the thermodynamic behavior of the gas inside the bubble are taken into account. The generalized model of the Kelvin or Maxwell type which consists of the spring, dashpot, and Kelvin units is used to describe the creep behavior of the material under combined stresses. The growth or shrinkage of the gas bubble may be induced by a change in the dissolved gas concentration in the material, a change in the external load applied to the material, or a combination of both. Numerical results are obtained for simpler models and the effects of their parameters on the radius‐time history of a bubble shrinking in an undersaturated solution or growing in an oversaturated solution are disclosed.