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Conformational dynamics of poly(lactic acid) (PLA) macromolecules have been studied in mixtures of PLA with its oligomer (OLA) depending on OLA concentration and temperature of the mixture. The study was performed using the recently developed A-graft-B coarse-grained model of the PLA (Figure 1). The force-field of the coarse-grained model was derived systematically using the VOTCA toolkit [1] to resemble the microscopic properties of OLA and PLA observed in all-atom computer simulations [2]. The systematic coarse-graining procedure ensured resemblance of radial distribution functions of non-bonded coarse-grained particles to the corresponding distributions calculated from all-atom computer simulations as well as distributions of bonded degrees of freedom including bonds, bend and dihedral angles. To provide better representation of the effects of degree of polymerization on mixture properties the interaction potential involving terminal units of polymer and oligomer were treated separately. The coarse- grained model revealed good reproduction of conformational properties of lactic acid polymer and oligomer and enabled an order of magnitude speed-up of the simulations.