Production of highly polymeric polymethylene terephthalates

Claim 1

A PROCESS FOR THE CONTINUOUS POLYCONDENSATION OF BIS-HYDROXYALKYL TEREPHTHALATE COMPRISING HEATING AND AGITATING SAID TEREPHTHALATE IN LIQUID FORM UNDER SUBATMOSPHERIC PRESSURE IN A SERIES OF RECTION ZONES EACH OF WHICH CONTAINS A POOL OF SAID REACTING LIQUID TEREPHTHALATE AND POLYALKYLENE TEREPHTHALATE, PASSING SAID TEREPHTHALATE AND ANY VAPORS EVOLVED DURING POLYMERIZATION THROUGH SAID ZONES IN SEQUENCE BY INTRODUCING SAID TEREPHTHALATE AND SAID VAPORS INTO EACH ZONE THROUGH AN INLET BELOW THE LEVEL OF THE LIQUID AND NEAR THE BOTTOM OF THE POOL OF LIQUID IN SAID ZONE, WITHDRAWING THEM FROM EACH ZONE AT A POINT SUBSTANTIALLY AT THE TOP OF THE LIQUID IN SAID ZONE, THEREBY PASSING THEM SUBSTANTIALLY THROUGH THE WHOLE DEPTH OF THE LIQUID IN SAID ZONE, AND THEN TRANSFERRING THE TEREPHTHALATE AND VAPORS THUS WITHDRAWN FROM EACH ZONE TO THE NEXT ZONE FOR INTRODUCTION BELOW THE LEVEL OF THE LIQUID AND NEAR THE BOTTOM OF SAID NEXT ZONE AND MAINTAINING SAID ZONES AT REDUCED PRESSURE AND SUCCESSIVELY LOWER PRSSURES ALONG THE PATH OF FLOW OF SAID TEREPHTHALATE, THE PRESSURE DIFFERENTIAL BETWEEN SUCCESSIVE ZONES BEING SUFFICIENT SO THAT THE PRESSURE DIFFERENTIAL DRAWS THE LIQUID FROM EACH ZONE TO THE NEXT AND INTERRUPTTING THE POLYMERIZATION BEFORE THE INTRINSIC VISCOSITY OF SAID LIQUID EXCEEDS O.5.