Determination of the structure of the noncrystalline regions in isotropic and oriented poly(ethylene terephthalate)

The mechanical properties of polymers are influenced strongly by the structure of the noncrystalline regions. The different methods for characterization of these regions are reported and the results obtained on polyethylene terephthalate, are discussed. The orientation function of the noncrystalline chains can be determined by measurements of the X‐ray scattering and the birefringence. The fraction of taut noncrystalline chains is obtained from NMR measurements combined with a determination of the degree of crystallinity. For a further evaluation of the results it is also necessary to use calculations of the NMR‐ line‐width and the birefringence of chains with fixeu ends. With help of such calculations the end‐to‐end distance of the taut and mobile non‐crystalline chains can be determined, It is also possible to distinguish between tie molecules and loops. With increasing orientation, the amount of taut noncrystalline chains increases. The taut chains are tie molecule rather than taut loops. The end‐to‐end distances increase with increasing crystallization temperature.