Polyester prepolymers and processes for their manufacture

Claim 1

IN A PROCESS FOR MANUFACTURING A PREPOLYMER WHICH IS A POLYESTER OF REACTANTS COMPOSED OF BIFUNCTIONAL DICARBOXYLIC ACID AND GLYCOL CONSTITUENTS AND WHICH HAS A MELTING POINT ABOVE 150*C. AND INCREASED REACTIVITY WHEN SUBJECTED TO SOLID PHASE POLYMERIZATION, WHICH PROCESS COMPRISE (A) INITIALLY FORMING A MOLTEN PREPOLYMER HAVING AN INTRINSIC VISCOSITY WITHIN THE RANGE OF FROM ABOUT 0.1 TO ABOUT 0.45 BY REACTING TOGETHER SAID GLYCOL AND A LOWER ALKYL DIESTER OF SAID DICARBOXYLIC ACID UNDER CONDITIONS OF MINIMUM REFLUX AND TURBULENT FLOW, (B) CASTING SAID MOLTEN PREPOLYMER UPON IN INERT SURFACE, (C) COOLING SAID MOLTEN PREPOLYMER TO THEREBY FORM A SOLIDIFIED PREPOLYMER, AND (D) SUBSEQUENTLY PULVERIZING SAID SOLIDIFIED PREPOLYMER; THE IMPROVEMENT WHICH COMPRISING IN STEP (B), CASTING SAID MOLTEN PREPOLYMER ONTO SAID INERT SURFACE TO THEREBY FORM A LAYER HAVING A THICKNESS OF FROM ABOUT 5 MM. TO ABOUT 35 MM., AND THEN COOLING SAID LAYER IN SUCH A MANNER THAT A CRUST FORMS THEREON AND THE MAXIMUM TEMPERATURE WITHIN SAID LAYER IS REDUCED TO BELOW ABOUT 125*C. IN FROM ABOUT 1 MINUTE TO ABOUT 5 MINUTES OF THE TIME SAID LAYER IS CAST; THE TEMPERATURE OF SAID MOLTEN PREPOLYMER BEING NOT MORE THAN 10*C. ABOVE THE CHARACTERISTIC MELTING POINT OF SAID PREPOLYMER AT THE TIME OF SAID CASTING.