Impact of lone pairs on the conformation and configuration statistics of poly(lactic acid) chains

Nonbonded interaction energies have been calculated for various conformations of the diester giving explicit consideration to the lone-pair electrons. As suspected from an earlier calculation on the dipeptide, such inclusion of the lone-pair effect leads to significant differences in the conformational potential energy map. The diester is shown to be more constrained than the dipeptide. The impact of this constrained geometry and the possible occurrence of cis residues on configuration statistics of poly(lactic acid) chains have been studied. Contrary to expectation the inclusion of cis isomers does not explain the paradoxical high negative temperature coefficient of ln C∞.