Block copolymers comprising poly(1,4-butylene adipate) or poly(1,4-butylene adipate-co-terephthalate) middle elastic segment and poly(glycidyl methacrylate-co-n-butyl methacrylate) side chains were obtained using the ARGET ATRP method. These copolymers were characterized by various average molar masses, compositions, numbers of epoxy groups per chain and epoxy equivalent weights and were utilized as reactive modifiers of polylactide (PLA) in extrusion type melt processing at 175 or 190 degrees C. Contrary to neat PLA processing, when modifiers of lower molar masses were applied then an increase in relative melt viscosity was observed in systems throughout the test run due to reactions of PLA-COOH with epoxy side groups in modifiers. The high molar mass modifiers were not as effective in compensation of the PLA degradation effect. Tensile strength properties of all the obtained compositions extruded in the form of thin strands were measured. Most of the obtained modifiers were able to enhance PLA in elasticity or/and strength. An aliphatic modifier acted as a reactive-internal plasticizer, therefore just slightly worsened the tensile strength but improved the elastic modulus and boosted elongation at break (it was up to 120 times higher than that of PLA). Although aliphatic-aromatic modifiers did not change elongation at break significantly, one of them reinforced and elasticized the PLA based system at once. (C) 2015 Elsevier Ltd. All rights reserved.