Method for producing highly condensed solid-phase polyesters

Method of producing polyesters having a desired I.V. value, the method comprising:

• a) crystallizing a polyester material in two stages in the presence of a gas with a dew point of less than or equal to −10° C. in the two stages, the first stage being carried out at a lower temperature than the subsequent stage;
• and
• b) setting the dew point of the gas to a particular value to obtain a desired rise of I.V. value of the polyester of
• (i) about 0 dl/g to about 0.02 dl/g and the dew point of the gas is set to about −10° C. to about −20° C.;
• (ii) about 0.02 dl/g to about 0.04 dl/g and the dew point of the gas is set to about −15° C. to about −25° C.;
• (iii) about 0.04 dl/g to about 0.06 dl/g and the dew point of the gas is set to about −20° C. to about −40° C.;
• (iv) about 0.06 dl/g to about 0.08 dl/g and the dew point of the gas is set to about −30° C. to about −55° C.;
• or
• (v) about 0.08 dl/g to about 0.1 dl/g and the dew point of the gas is set to about −45° C. to about −75° C.