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Abstract

Disclosed is a process for the manufacture of high molecular weight polyesters, particularly poly(ethylene terephthalate) (PET) and modified PET, having inherent viscosities (I.V.) for example, above about 0.6, and up to about 1.3 or higher. Such polymers are useful, for example, as structural moldings, self-supporting sheets and films, and blow-molded bottles. The process involves one or more recrystallizations of the polymer incident to solid-state polycondensation, which recrystallizations, it has been discovered, restores the high polycondensation activity of the polymer experienced in the early stages thereof and allows greatly increased overall build-up rate and higher final I.V. for the total polycondensation period. The process is particularly applicable to crystallizable polyesters in general which lend to solid-state build-up.

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