Polyester Polymer Particles Having a Small Surface to Center Molecular Weight Gradient

Abstract

There is now provided a polyester polymer particle having an It.V., a surface, and a center, wherein the It.V. at the surface of the particle is less than 0.25 dL/g higher than the It.V. at the center of the particle. The polyester polymer particle is desirably crystalline to prevent the particles from sticking to each other while drying, and desirably contains less than 10 ppm acetaldehyde. A polyester container, preferably a preform or beverage bottle, is made by feeding crystallized polyester particles having an It.V. of at least 0.70 dL/g to an extrusion zone, melting the particles in the extrusion zone to form a molten polyester polymer composition, and forming a sheet or a molded part from extruded molten polyester polymer, wherein at least a portion of the polyester particles have an It.V. at their surface which does not vary from their It.V. at their center by more than 0.25 dL/g, and the particles have not been solid state polymerized. Such polyester compositions have an It.V. suitable for containers, yet lose less It.V. during melt processing than existing polyesters.

1 . A polyester polymer particle comprising a polyester polymer comprising:
 (a) a carboxylic acid component comprising at least 90 mole % of the residues of terephthalic acid, derivates of terephthalic acid, naphthalene-2,6-dicarboxylic acid, derivatives of naphthalene-2,6-dicarboxylic acid, or mixtures thereof, and   (b) a hydroxyl component comprising from 90 to 96 mole % of the residues of ethylene glycol,   
       based on 100 mole percent of the carboxylic acid component residues and 100 mole percent hydroxyl component residues in the polyester polymer, wherein said particle has an It.V. of at least 0.70 dL/g, and the It.V. at the surface of the particle is less than 0.25 dL/g higher than the It.V. at the center of the particle. 
     
     
         2 . The particle of  claim 1 , wherein the particle has an It.V. of at least 0.74 dL/g. 
     
     
         3 . The particle of  claim 2 , wherein the particle has an It.V. of at least 0.77 dL/g. 
     
     
         4 . The particle of  claim 2 , wherein the It.V at the surface of the particle is less than 0.2 dL/g higher than the It.V. at the center of the particle. 
     
     
         5 . The particle of  claim 1 , wherein the It.V. at the surface of the particle is less than 0.15 dL/g higher than the It.V. at the center of the particle. 
     
     
         6 . The particle of  claim 1 , wherein the particle has a degree of crystallinity of at least 25%. 
     
     
         7 . The particle of  claim 1 , wherein the particle contains less than 10 ppm acetaldehyde. 
     
     
         8 . Polyester particles having a number average weight of at least 1.0 g per 100 particles, wherein each particle is the polyester particle of  claim 1 . 
     
     
         9 . The polyester particle of  claim 1 , wherein said polyester particle is a virgin polyester polymer.