Optical activity of poly-L-lactic acid in crystalline and dissolved states

The symmetry changes of the gyration tensor components of the solid polymers with a spiral orientation are clarified with respect to the changes of the density distribution function of the constituent crystallites. Any constituent crystals of optically active polymers should be regarded as uniaxial and enantiomorphic as far as the gyration is concerned. When the density distribution becomes perfectly homogeneous in the three-dimensional space, the gyration tensor components are reduced to a single component, g. Two rotatory powers of poly-L-lactic acid are compared; one is calculated from measured values in the solid state, the other is a measured value in chloroform solution by Goodman and D'Alagni. It is striking that the former is 10³ times larger than the latter. This means that the helical conformations of the residues which clearly exist in the solid state are destroyed in the liquid solution.