Process for preparing aromatic polyesters from diphenols

In a process of preparing linear aromatic polyesters by reacting in a molten state (A) a member selected from the group consisting of aromatic dicarboxylic acids and lower alkyl esters and aryl esters thereof with (B) a diphenol to prepare a polymer and thereafter polymerizing the thus obtained polymer in the solid phase, the improvement which comprises carrying out said reaction in the presence of (C) at least one member selected from the group consisting of the dihydroxy compounds, bisglycol esters of dicarboxylic acids and glycol esters of hydroxycarboxylic acids, said dihydroxy compound selected from the group consisting of a straight chain or branched chain aliphatic glycol of 2 - 12 carbon atoms, an alicyclic glycol and a compound having attached to its aromatic nucleus two members of the class consisting of hydroxyalkylene and hydroxyalkyleneoxy groups, the alkylene portion of which contains 2 - 6 carbon atoms, the components (B) and (C) being used in proportions, based on (A), of 70 - 105 mol % of (B) and 1 - 50 mol % of (C), the total amount of (B) and (C) corresponding to 100 - 130 mol % of (A).