FIELD: manufacture of high molecular polyester resins. SUBSTANCE: low molecular polyester resin which contains ethylene phthalate and/or ethylene isophthalate links is mixed in extruder with 0.1-0.38% by weight of resin with additive which promotes high viscosity of resin. The additive includes pyromellitic or 3,3I, 4,4I- benzophenone tetracarboxylic acid dianhydrides, mixture is granulated and solid phase polycondensation is carried out in reactor at 170-216 C for 3-8 hours. Mixing is carried out in twin screw repulsion type extruder, screws being disengaged in vacuum of from 20 to 120 millibar. The molten resin has temperature of form 298 to 302 C in the extruder and its residence time amounts to 35-50 s. The additive is essentially dispersion in polyester resin powder. Solid phase polycondensation time is reduced and intrinsic viscosity of resin is increased to 0.78-1.36 dl/g. EFFECT: improved properties of the resin. 5 cl, 4 tbl
