Abstract: A stereospecific poly(lactic acid) is isotactic poly(lactic acid) having a number average molecular weight ranging from 10,000 to 200,000 grams per mole, with, on average, an equal number of poly (R) and poly (S) blocks where each block contains an average of 5 to 50 monomer units. Product was prepared by polymerizing rac-lactide in the presence of racemic catalyst consisting of: and the corresponding S-enantiomer or in the presence of racemic catalyst consisting of: and the corresponding S-enantiomer, wherein R is C1-C4 alkyl which is straight chain or branched.

Abstract: A stereospecific poly(lactic acid) is isotactic poly(lactic acid) having a number average molecular weight ranging from 10,000 to 200,000 grams per mole, with, on average, an equal number of poly (R) and poly (S) blocks where each block contains an average of 5 to 50 monomer units.

Abstract: Isotactic poly ((R)-lactic acid) or isotactic poly (S)-lactic acid are respectively prepared from (R,R)-lactide and (S,S)-lactide using a catalyst which has a zinc center or a magnesium center and two ligands where one of the ligands is a propagating group and the other of the ligands is not a propagating group. Heterotactic poly(lactic acid) is prepared from rac-lactide using a catalyst which has a zinc center and two ligands where one of the ligands is a propagating group and the other of the ligands is not a propagating group; heterotactic poly(lactic acid) is a novel composition. The catalyst with a magnesium center is a novel catalyst.

Abstract: Polycarbonates having M.sub.n ranging from about 5,000 to about 40,000 and a molecular weight distribution ranging from 1.05 to 2.0 are prepared from epoxides and CO.sub.2 using a catalyst which has a Zn center and two ligands where one of the ligands is a propagating group and the other of the ligands is not a propagating group and an activity of at least one turnover per hour, preferably at least 100 turnovers per hour. Preferred catalysts have a ##STR1## moiety with group on each nitrogen containing a phenyl moiety.

Abstract: Novel elastomeric alpha olefin polymers of homogeneous composition formed from linear or branched chain C.sub.3 -C.sub.10 monomers such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene and mixtures thereof, comprising alternating isotactic and atactic disastereosequences in which all polymer fractions have similar molecular weight distributions, M.sub.W /M.sub.n, of less than 7, an isotactic Block Index greater than about 5, an isotactic pentad, mmmm, content of between 9 and 71%, an average molecular weight, Mw, from about 20,000 to about 1,350,000, a melting point of above 70.degree. C., and which polymers are elastomeric in exhibiting a positive power of recovery of elongation above 100%. Examples include thermoplastic elastomeric polypropylenes having melting points between 70-165.degree. C., which are highly regioregular and have low tensile set of below about 70.degree. at 300% elongation.

Abstract: This invention is directed to novel catalysts the structure and activity of which can be controlled to produce a wide range of alpha olefin polymers and co-polymers, and preferably for the production of stereoblock poly alpha olefins comprising a wide range of preselected amorphous and crystalline segments for precise control of the physical properties thereof, principally elastomeric thermoplastic properties. More specifically, this invention is directed to novel catalysts and catalysts systems for producing stereoblock polypropylene comprising alternating isotactic and atactic diastereosequences, which result in a wide range of elastomeric properties. The amount and numbers of crystalline sections, the isotactic pentad content, the number and length of intermediate atactic chains and overall molecular weight are all controllable by the steric structure of the catalysts and the process conditions.