FIELD: polymer production. SUBSTANCE: amorphous prepolymer of polyethylene naphthalate or its copolymer with polyethylene terephthalate containing volatile components is crystallized by heating prepolymer granules or cuttings to temperature lying between temperature by 20 C higher vitrification temperature and temperature by 10 C below melting point at stirring and superatmospheric pressure equal to at least vapor pressure of volatile components until crystalline prepolymer of homo- or copolymer is obtained. High-molecular polyethylene naphthalate homo- or copolymers with intrinsic viscosity at least 0.5 dl/g are prepared by polymerization of corresponding crystalline prepolymers under conditions required for conversion into solid state at temperature from 50 C to temperature by 1 C below prepolymer softening temperature during period of time sufficient to form high-molecular homo- or copolymer. EFFECT: enabled crystallization of prepolymer at positive pressure thereby avoiding deformation of prepolymer granules upon crystallization. 10 cl, 2 tbl, 4 ex
