In ethylene copolymers isolatedCH2CHRCH2 groups undergo a glass transition at about −10 to −50°C., the exact temperature depending upon the nature of R. For any given copolymer the temperature of the transition remains reasonably constant over a broad composition range at high ethylene contents. At high comonomer content the transition rises with composition along the line drawn between the glasstransition temperature of polyethylene and that of the homopolymer of the comonomer in question. A second glass transition is also observed in ethylene copolymers at about −125°C. over the whole composition range. This transition corresponds to motion of CH2 sequences of three to five or more in the main chain. The temperature position of this transition is usually independent of the nature of the rest of the chain. The behavior of ethylene copolymers is quite different from that of normal vinyl copolymers, where only a single glass transition is observed for each composition and where the temperature position of the transition changes uniformly with composition along the line drawn between the glass transitions of the respective homopolymers. It is concluded that the motions involved in the glass transitions of the main chain CH2 sequences and of isolated CH2CHRCH2 groups in ethylene copolymers are localized, involving only a few carbon atoms. In the case of the normal vinyl copolymers, on the other hand, the motion at the transition appears to be a long‐range motion involving a great many chain carbon atoms and cooperative motion of the pendent groups. This change in the nature of the motion involved at the glass transition in going from high ethylene content copolymers to low ethylene content or vinyl copolymers appears to arise because of steric hindrance and/or restrictive dipolar forces between the pendent groups of the CH2CHRCH2 segments in those cases were they are not isolated from each other. Finally, it is concluded that all vinyl homopolymers would have glass transitions in the −10 to −50°C. range if steric hindrance between the side groups did not occur. It is shown that as the pendent group becomes less bulky or is further separated from the main chain by CH2groups the glass transition temperature decreases presumably towards the −10 to −50° range characteristic of the transition of isolated CH2CHRCH2 groups.

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Infrared spectra of thin non-scattering films of NH3 and ND3 were obtained at −190°C. All four fundamentals of both compounds were observed with no evidence of inversion doubling of ν2. The crystal spectrum of NH3 suggests a frequency near 3450 cm−1 for ν3 in the gas. The spectra are in agreement with a molecular crystal having the reported x-ray symmetry T4. Two of the five torsional lattice vibrations were probably observed directly and one more strongly indicated in combination bands. A fourth lattice frequency of 53 cm−1 also occurs in combination bands. Since the coupling between the various internal vibrations and between the lattice and internal vibrations proved to be small, the potential function of the crystal was assumed to be separable into an internal and a lattice problem. A normal coordinate treatment of the internal vibrations fits all frequencies to better than one percent.