Isotactic poly(β-methyl-β-propiolactone)
(poly(CH3-PL)) and
poly(β-ethyl-β-propiolactone)
(poly(C2H5-PL)) with (S) and
(R) configurations, respectively, were synthesized in yields
of 70% via the
polymerization of optically active
β-(trichloromethyl)-β-propiolactone (CCl3-PL) and
β-(dichloroethyl)-β-propiolactone (CH3CCl2-PL). The
polymerization was conducted in bulk, under vacuum, using
the
triethylaluminum/water or the diethylzinc/water catalysts. These
polymerizations were followed by the
dechlorination of the resulting chlorinated polymers, using the
tri-n-butyltin hydride (Bu3SnH)
reducing
agent. 13C NMR spectroscopy shows that all the
chlorinated and dechlorinated polymers have a degree
of isotacticity of 100%, indicating that little or no racemization
occurs during the course of the
polymerization. Atactic homologues were also synthesized; these
are soluble in the usual organic solvents,
contrary to the isotactic polymers. Multiangle laser light
scattering analyses of atactic polymers indicate
that the dechlorination reaction occurs with some degradation, leading
to poly(CCl3-PL) and
poly(CH3CCl2-PL) with molecular weights of about 5000. The
variations of the glass transition temperature, melting
temperature, and enthalpy of fusion with the dechlorination ratio are
discussed. The whole analysis
shows that the dechlorination reaction generates statistical
copolymers, with the formation of the
intermediate homopolymers poly(CHCl2-PL) and
poly(CH2Cl-PL) in the case of the dechlorination of
poly(CCl3-PL). X-ray patterns show that each homopolymer
has its own crystalline structure and that the
semicrystalline copolymers adopt a crystalline structure similar to
that of the homopolymer of closest
composition.