Synthesis and polymerization of racemic and optically active substituted ß‐propiolactones. V. α‐methyl ß‐propiolactone

Abstract

AbstractR(+) and S(−) enantiomers of α‐methyl β‐propiolactone (MPL) have been synthesized from the corresponding α‐methyl β‐hydroxymethylpropionates and racemic MPL from methyl methacrylate. The optical purity and absolute configuration of these lactones were determined using 1H‐NMR spectroscopy after complexation with a chiral compound: 2,2,2‐trifluoro‐1‐(9‐anthryl)‐ethanol. Optical purities of 100% were obtained for both the S(−) ([α0] = −10.4°, c = 1.3 g/dL in CHCl3) and the R(+) ([α0] = +10.5°, c = 1.0 g/dL in CHCl3) enantiomers. The corresponding racemic and optically active polylactones [poly(MPL)] were prepared by anionic polymerization, in bulk and in solution, as well as poly(MPL)s of intermediate optical purities. The polymers thus obtained are optically active ([α0] = 16.2° in CHCl3 for the optically pure polymer, S configuration) and exhibit significant differences. For example, the racemic poly(MPL) is soluble in several organic solvents such as tetrahydrofuran, benzene, CCl4, CH2Cl2, hexafluoroisopropanol, and CHCl3, whereas the optically active poly(MPL)s are soluble in CHCl3 and hexafluoroisopropanol only. Moreover, racemic poly(MPL) is amorphous whereas optically active poly(MPL)s are semicrystalline for optical purities larger than 51%. Melting temperatures and enthalpies of fusion of the semicrystalline polylactones vary with optical purity whereas glass transition temperatures remain invariant for all polymers, at about −28°C. The poly(MPL) of highest optical purity exhibits a melting temperature of 95°C and an enthalpy of fusion of 61 J/g.