The structural configurations that distinguish the atactic phase from the isotactic phase give rise to infrared spectra characteristic of each phase. Since these differences are quite significant, a method is proposed with which the isotacticity can be determined. The relation between the isotactic phase and crystallinity is considered, and its application to this study is discussed. The formation of oxygen‐containing degradation products was followed during accelerated oxidation and the products identified. There is also evidence that more numerous oxygen containing degradation products form in polypropylene than in polyethylene. The type of unsaturation was also determined, and its presence confirmed by chlorination.
The changes in the molecular structure of polyethylene during oxidation are studied. The presently accepted theory involves a free‐radical process and is based largely on measurements of reaction kinetics with model compounds. Infrared spectroscopy afford an alternate method of following the course of the oxidation reaction. By recording the infrared spectra of polyethylene samples during oxidation, it was possible to follow continuously the formation of various oxygen‐containing groups. During the early stages of oxidation, the formation of hydroperoxides was noted, as was their subsequent decomposition into the predominant secondary oxidation products. The alpha carbon was found to be quite susceptible to oxygen attack after autocatalytic oxidation had begun, and a resulting decrease in methylene content was observed. The results provide a description of the oxygenated molecular groups that form during the initial stages of oxidation and support and broaden the presently accepted mechanism for the oxidative degradation in polyethylene.
The transformations of the polymorphic forms of polybutene‐1 (I,II,III) were studied by infrared spectroscopy. Attenuated total reflectance spectra demonstrate that the II → I transformation occurs initially and most rapidly on the film surfaces. Electron irradiation experiments showed the II → I conversion can be suppressed by irradiation. The degree of suppression was dependent on the irradiation dose. Comparison of spectra on irradiation in air and vacuum indicate that radiation‐produced radicals are scavenged by oxygen, preventing intermolecular crosslinking and allowing normal expansion of the helix during transformation. In addition, remolding an irradiated sample of II caused immediate conversion to I rather than its return to II as was noted when unirradiated samples are remolded. These observations are related to certain conformational changes in the molecular structure.
Silicon nitride,
Si3N4
, used as a passivating layer in microelectronics, exists in the crystalline forms
α‐Si3N4
and
β‐Si3N4
and as amorphous material. Although the two crystalline modifications differ only slightly in their structure, it has been found that each modification can be distinguished by infrared spectroscopy. The spectral characteristics of
α‐normaland β‐Si3N4
are described and a method for determining the concentration of one phase in the presence of the other has been developed.
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