DETAILED DESCRIPTION OF THE INVENTION Optically active R- and S-enantiomers of lactic acid and of the lactides are commercially available and can be homopolymerized or copolymerized by known methods such as bulk (co)polymerization usually in a dry, inert atmosphere with an ionic catalyst such as stannous octanoate.
The resultant enantiomeric poly(lactides), after purification e.
g.
, by precipitation from solution in a suitable solvent such as methylene chloride or chloroform by addition of a non-solvent such as diethyl ether, have crystalline melting points of 173.
degree.
to 177.
degree.
C.
Lactide copolymers will generally have lower crystalline melting points, depending on lactide content but may be amorphous.
It should be understood that the term "copolymers" as used herein includes polymers prepared from mixtures of R- and S-lactide as well as from R- or S-lactide and at least one non-lactide comonomer.
Examples of suitable non-lactide comonomers include those capable of condensation polymerization with lactide or lactic acid, i.
e.
, lactones such as epsilon-caprolactone, beta-propiolactone, alpha,alpha-dimethyl-beta-propiolactone, delta-valerolactone, alpha-, beta- or gamma-methyl-epsilon-caprolactone, 3,3,5-trimethyl-epsilon-caprolactone, dodecanolactone; lactams; other hydroxy acids such as glycolic acid; amino acids and the like.
Operable copolymers will in general contain blocks of lactide of sufficient length such that the copolymer exhibits a crystalline melting transition characteristic of lactide, although enantiomerically balanced compositions of certain amorphous lactide copolymers may also exhibit a crystalline melting transition, reflecting the novel phase.
Especially useful thermoplastic elastomeric compositions are comprised of two block copolymers containing, respectively, lactide blocks of opposite enantiomeric configuration and "soft" blocks of polyether, polyester or other similar polymer.
The present composition can contain non-lactide polymers, fillers and other known additives
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