Patent ID: 7196159

Claim:
A process for the production of polytrimethylene terephthalate (PTT) having controlled levels of dipropylene glycol, comprising: (i) contacting 1,3-propanediol with terephthalic acid or an alkyl diester of terephthalic acid in the presence of a protic acid other than terephthalic acid or isophthalic acid having a dissociation constant (pKa) of at most 4, as measured in water at 25° C., to produce an esterification product in one or more esterification steps; (ii) polycondensing the esterification product to form polytrimethylene terephthate; wherein the protic acid is present in the one or more esterification steps in an amount of from 0.001 to 10 millimole of protic acid per kilogram of polytrimethylene terephthalate produced.