Process for controlling the change of intrinsic viscosity and
transesterification during solid stating of a polyethylene terephthalate
(PET) and polyethylene naphthalate (PEN) blend, with an effective amount
of an ethylene glycol compound. The process enables the production of a
copolymer based on predefined initial and final IV's and final
transesterification level, by varying the solid-stating time and/or
effective amount of ethylene glycol. In one embodiment, a relatively
greater amount of post-consumer PET (e.g., 70%) having an IV of on the
order of 0.72-0.73, is incorporated in the blend to provide a final IV on
the order of 0.80-0.85, and a moderate, controlled level of
transesterification; the blend is used to injection mold a sleeve layer of
a preform. In another embodiment, a substantially transparent neck finish
for a preform is made from a PEN/PET blend having an amount of ethylene
glycol which enables substantial transesterification, without excessive
increase in IV.