Abstract: The invention discloses polymeric esters of terephthalic acid with deagglomerated barium sulphate having an average primary particle size of less than 0.5 ?m, containing a crystallization inhibitor and being coated with a dispersant, as filler. The dispersant has preferably reactive groups which are able to interact with the surface of the barium sulphate; particular preference is given to dispersants which are able to endow the barium sulphate with a hydrophilic surface and have reactive groups for coupling to or into polymers. Also disclosed is a corresponding precursor based on macrocyclic oligoesters which comprise such barium sulphate.