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SynopsisUltraviolet and Fourier-transform infrared spectroscopy are used to characterize the chain conformation of 2,6-dimethyl poly(pheny1ene oxide) (BMPPO) in compatible BMPPO-polystyrene (PSI blends. Blending with PS increases the intramolecular energy of the BMPPO. Atactic PS induces a greater distortion from the minimum energy conformation of BMPPO than isotactic PS. The dispersion interaction between the phenyl ring of PS and the phenylene ring of BMPPO is found to be quite strong. These large intermolecular forces are thought to supercede the increase in BMPPO conformational energy and to be responsible for the blend compatibility.

Poly(tetramethylene terephthalate) (PTMT) undergoes a reversible stress‐induced crystal‐crystal phase transition. X‐ray fiber‐diffraction photographs were obtained from the oriented, unstressed (α) phase. Relative intensities were measured from these photographs. These were used to help check the reported structures of the α phase. Structures and observed intensity data from other authors were also utilized. Results show the α phase contains a non‐trans, non‐gauche bond rotation in the tetramethylene chain and a nonplanar terephthalic acid residue. A tilt of 3.5° between the fiber axis and the c axis was determined in a direction 210° counterclockwise from the b* axis.

Measurements of infrared absorbance as a function of temperature down to 77°K have been made on poly(ethylene terephthalate). Transitions observed by other techniques such as torsion pendulum measurements are reflected in the infrared measurements by an abrupt change in the slope of the absorbance versus temperature. The infrared measurements are made on bands of known structural origin so the structures contributing to each transition can be determined. The β transition is shown by infrared to be a composite of two peaks with the lower‐temperature portion arising from the amorphous regions and the higher‐temperature portion from the crystalline regions.

The reversible stress‐induced crystal‐crystal phase transition of poly(tetramethylene terephthalate) (PTMT) has been studied using infrared spectroscopy. Two spectral regions were used to study this transition: the 900–1000 cm−1 methylene rocking region and the 1300–1550 cm−1 methylene bending region. The bands at 917 and 1456 cm−1 are assigned to the ∝ phase. The bands at 935 and 1388 cm−1 have components from the α phase and the β phase. Dynamic stretching experiments performed above and below the glass‐transition temperature indicated different mechanisms of the phase transition.