Process for the manufacture of linear polyesters with metal imide salt catalysts

Linear polyesters are made by polycondensing a bis-glycol ester of a dicarboxylic acid in the presence of a metal salt of an acid imide as catalyst. Specified catalysts are the Ca, Mg, Zn, Cd, La, Ge, Sn, Pb, Ti, Sb, Bi, Mn and Co salts of phthalimide, 1 :8-naphthalene dicarboxylic acid imide, pyromellitic acid di-imide and succinimide. The bis-glycol esters are preferably made by reesterifying a diester of a dicarboxylic and a glycol and as catalyst for the pre-esterification there may be used either (a) a metal salt of an acid imide, possibly of a metal different from that used as polycondensation catalyst, or (b) zinc acetate. Specified dicarboxylic acids are adipic, sebacic, trans-1 : 2 - cyclobutanedicarboxylic, terephthalic, 1 : 4 - naphthalene dicarboxylic, 4 : 41 - diphenyl dicarboxylic, 4 : 41-sulphonyl dibenzoic and 2 : 5-thiophene dicarboxylic acid. Specified glycols are ethylene glycol and its homologues, diethylene glycol, 2 : 2-dimethylpropane diol and 1 : 4-dimethylol cyclohexane. Examples describe the manufacture of polyethylene terephthalate from dimethyl terephthalate and ethylene glycol.