Preparation of improved linear copolyesters employing two stages to polymerize solidparticles

A process for the solid phase polymerization of initial prepolymer copolyester particles having sizes substantially passing a 20 U.S. mesh screen with less than 25% passing a 200 mesh screen and having an inherent viscosity not exceeding 0.5, comprises (I) heating the particles at 170 DEG to 300 DEG C. for at least 1 1/2 hours to produce a product having an inherent viscosity not more than 0.1 units higher than the initial prepolymer, and (II) heating this product at a temperature of at least 20 DEG C. below the melting-point of the final product until a copolyester is produced having a melting point at least 10 DEG C. higher than the same copolyester produced by a single-stage process. The process is stated to produce block-type copolyesters. The copolyester is that of (a) at least one glycol at least 75 mole per cent of which is the cis- or trans-isomer of 1: 4-cyclohexanedimethanol, (b) at least one dibasic acid of which at least 60 mole per cent is a dicarboxylic acid in which each carboxyl group is attached to a single carboxylic nucleus or different carbocyclic nuclei. The modifying glycol may be ethylene glycol, 1: 5-pentandiol, 1: 10-decanediol, diethylene glycol, triethylene glycol, 2: 2-dimethyl - 1: 3 - propanediol, 2 - methyl - 1: 5 - pentanediol or 1: 4-di(hydroxyethyl)benzene. The carboxylic dicarboxylic acid may be terephthalic, trans-hexahydroterephthalic, p: p1-sulphonyldibenzoic, 4: 41-diphenic, 4: 41-benzophenonedicarboxylic or 1: 4- or 1: 5-naphthalene dicarboxylic acids, or may be 1: 2-di(p-carboxyphenyl)ethane, 1: 2-di(p-carboxyphenoxy)-ethane or 4: 41-dicarboxydiphenyl ether. Up to 40 mole per cent of these acids may be replaced by carbonic, oxalic, succinic, adipic, sebacic, azelaic, alpha, ethylsuberic, alpha, alpha-diethyladipic, dimethylmalonic, orthophthalic, itaphthalic or hexahydro-orthophthalic acids or by dicarboxyl diethyl ether. The polyesters may also be modified by hydroxypivalic, hydroxybutyric or hydroxycaproic acid. Both stages of the solid phase polymerization may be effected in a horizontal or vertical polymerization zone and in a vacuum or a current of an inert gas. The particles may be stirred or a fluidized technique may be used. Examples describe the solid phase polymerization of polyesters of: (1)-(11) and (15) terephthalic acid, succinic acid or glutaric acid or sebacic acid or azelaic acid, and a mixture of trans- and cis-cyclohexane -1: 4-dimethanol; (12) terephthalic acid, glutaric acid, succinic acid, and