On the location of chain‐ends in rapidly crystallized poly(ethylene terephthalate)

Phenylmercurated poly(ethylene terephthalate) (PET) chain‐ends are obtainable through the transesterification of PET by phenylmercury hydroxide or acetate in solution in nitrobenzene at 165 ± 10°C. The reaction results in an average of one mercury atom per chain. The phenylmercuration may be followed by infrared or x‐ray fluorescence. Reaction with concentrated HCI Affords the elucidation of some structural parameters of the resultant partially crystalline tagged PET, through analyses of changes in viscosity and molecular weight, in percent crystallinity, and in the amount of mercury in the system. The chain‐ends are almost completely excluded from the stem region of the PET crystal with no more than 2% remaining. The chain‐ends are distributed unevenly throughout the amorphous phase. This is corroborated by sharp decreases in scattered intensity of small‐angle x‐ray measurements. Two models for the distribution of chain‐ends in the amorphous phase are considered. The one in which the ends are pushed farthest from the crystal surface and concentrate halfway between crystallites is tentatively adopted. Analysis of the HCI hydrolysis kinetics and products leads to the following picture concerning the fold tightness and position. About one out of five folds extends significantly into the amorphous matter where it is mingled with cilia, tie molecules, and unattached molecules. Random scission throughout such an amorphous mass should lead to a preponderance of cleaved molecules whose length should be four to five times the lenght of the crystalline stem region, as is indeed observed.