P. Schmidt

A study was made of the structural and property changes that occur when poly(ethylene terephthalate) films are oriented, crystallized, and thermally relaxed. X-ray diffraction, infrared, density, and stress-strain measurements were used to develop information on the amount and direction of orientation of both the crystalline and amorphous regions of these films. Three structural factors influence resultant film properties: (1) the kind and perfection of crystallite orientation, (2) the amount and direction of the trans-gauche isomerization in the amorphous regions, and (3) the amount of crystallinity. Interactions of these factors result in substantially different film properties and relaxation behavior. Of special significance is the influence of “taut” extended amorphous regions produced by orientation which generate useful structure-property information.

Abstract The absorption intensity of a given infrared absorption band, in the infrared spectrum of an oriented polymer is composed of an orientation and a structural factor. A method is discussed, using polarized infrared radiation, which will measure the contribution of each. The ethylene glycol linkage of the polyethylene terephthalate molecule may exist in either of two forms. These forms are rotational isomers. The trans form of the molecule is the extended form, the gauche form is the relaxed form. The amorphous regions of polyethylene terephthalate films have been found to contain both of these isomers. Polymer orientation is summarized in terms of transition moment types. Orientation parameters characteristic of polyethylene terephthalate films are defined.

Ordered structures in samples of Bisphenol A polycarbonate (BPAPC) prepared by varying thermal and solvent conditions were investigated by infrared and Raman spectroscopy, wide-angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC). Based on the spectroscopic analysis and ab initio quantum mechanical calculations of diphenyl carbonate as a model compound, an assignment of the bands conformationally sensitive to the trans−trans and cis−trans structures is proposed. Temperature dependences of the vibrational spectra of BPAPC show that cis−trans structure is the energetically preferred conformation in the amorphous state and in solution and its population can be increased with decreasing temperature in amorphous BPAPC even below the glass transition temperature. Differences in the degrees of ordering in semicrystalline BPAPC assessed from the vibrational spectra, WAXS, and DSC indicate partial order in the interfacial region between the crystalline and amorphous phases. In some solvents (toluene, benzene), aggregation of BPAPC occurs, leading to the ordered structure analogous to crystalline BPAPC. The order is preserved in semicrystalline BPAPC obtained by the room-temperature evaporation of the solvent.