A continuous process for the production of poly(trimethylene
terephthalate) is disclosed. According to the process, a liquid feed
mixture comprising bis-3-hydroxypropyl terephthalate and/or low molecular
weight polyesters of 1,3-propanediol and terephthalic acid, the liquid
feed mixture having a mole ratio of propylene groups to terephthalate
groups of 1.1 to 2.2 is fed to a flasher. A first stream of gaseous
by-products is continuously vaporized and removed from the flasher, and a
liquid flasher reaction product having a mole ratio of propylene groups
to terephthalate groups of less than about 1.5 is continuously withdrawn
from the flasher. The liquid flasher reaction product is continuously fed
to a prepolymerizer where it is continuously polymerized to form a
poly(trimethylene terephthalate) prepolymer and a second stream of
gaseous by-products. Poly(trimethylene terephthalate) prepolymer having a
relative viscosity of at least about 5 is continuously withdrawn from the
prepolymerizer and continuously fed to a final polymerizer, where it is
continuously polymerized to form a higher molecular weight
poly(trimethylene terephthalate) and a third stream of gaseous
by-products. Higher molecular weight poly(trimethylene terephthalate)
having a relative viscosity of at least about 17 is continuously
withdrawn from the final polymerizer.