A DFT study on poly(lactic acid) polymorphs

摘要: Abstract Poly(lactic acid) (PLA) can crystallize in α-, β-, γ- and stereocomplex (sc)- forms. It has been shown that the formation of between poly( l -lactic d significantly improve thermal stability mechanical properties. However mechanisms enhancements are still unclear. In this study, we investigate PLA polymorphs from first-principles theoretical perspective order to understand intermolecular interaction crystals. Density functional theory at level Perdew-Wang generalized-gradient approximation was applied optimize crystal unit cells. A comparison energies various cells reveals sc-form is most energetically favorable form among four polymorphs. The thermodynamically relative 0.3, 1.1, 1.3 kcal/mol more stable than α-form, β-form, γ-form, respectively (when using ultrasoft pseudopotential a plane-wave basis set with an energy cutoff 380 eV) or 0.4, employing density semi-core pseudopotentials double numerical plus polarization orbital global 3.7 A). addition energetic properties, structural electronic properties were calculated as well. predicted rank agreement some reported observations. Such as, higher melting point larger heat fusion those α-form. enhanced compared other three homopolymer forms may be attributed unique non-conventional hydrogen bonding C–H⋯O( C) network stereocomplex.