Title
Optically Active Precision Aliphatic Polyesters via Cross‐Metathesis Polymerization
Author
Fu‐Rong Zeng, Ji‐Mei Ma, Lin‐Hao Sun, Zhen Zeng, Hong Jiang, Zi‐Long Li
Year
2018
Journal
Macromolecular Chemistry and Physics
Abstract
Precision synthesis of optically active poly(lactic‐alt‐caprolactic acid) is realized using cross‐metathesis polymerization (CMP) and hydrogenation. Enantiopure monomers MLand MD are generated through two consecutive esterification reactions. CMP of these two monomers in different feed ratios, followed by hydrogenation, afford saturated polymers HPL, HPD, and HPDL comprising L‐lactic and/or D‐lactic acid and ε‐caprolactone‐derived motifs with alternating sequences. CMP kinetic analysis by nuclear magnetic resonance (NMR) is performed by employing a racemic monomer Mrac. Enantiomeric polyesters HPL and HPD display opposite rotation values and mirror‐imaged cotton effects in circular dichroism (CD) spectra, whereas HPDL derived from equimolar ML and MD shows inactive optical rotation and no CD response. Stereocomplex HPD+HPL is obtained by equimolar mixing of HPL and HPD, since this specimen is the only one to exhibit a sharp melting peak on differential scanning calorimetry (DSC) curve at 45.7 °C. Hence, an amorphous, enantiomerically pure polyester becomes crystalline via stereocomplexation with its complementary enantiomer.
Instrument
J-1500
Keywords
Circular dichroism, Stereochemistry, Cotton effect, Polymers