Abstract: The present invention relates to a reactive mixture, comprising poly(hydroxyalkanoic acid) or copolymer thereof and a reactive composition adapted such that a relatively rubbery phase is formed once reacted. Preferably the reactive composition is polymeric and comprises at least first and second reactable components which preferably contain epoxide moieties and carboxylic moieties respectively. The present invention also relates to a method for providing a reactive mixture, the method comprising the steps of combining poly(hydroxyalkanoic acid) or copolymer thereof, a first polymer having epoxide moieties and a second polymer having carboxylic moieties. The invention also relates to a method for controlling the melt viscosity of a polymeric mass during melt processing.