Poly defined isotactic-syndiotactic

Mesomorphic forms characterized by conformationally ordered polymer chains packed in lattices with different kinds of lateral disorder have been described for various isotactic and syndiotactic polymers. For instance, for iPP,706 sPP,201 sPS,202 syndiotactic poly(p-methylstyrene) (sPPMS),203 and syndiotactic poly(m -methylstyrene),204 mesomorphic forms have been found. In all of these cases the X-ray fiber diffraction patterns show diffraction confined in well-defined layer lines, indicating order in the conformation of the chains, but broad reflections and diffuse haloes on the equator and on the other layer lines, indicating the presence of disorder in the arrangement of the chain axes as well as the absence of long-range lateral correlations between the chains. 

Zinc alkoxides have also been prepared by reaction of diethylzinc with alcohols. Zn(0-ra-C4H9)2 was studied by Kricheldorf (4). C2H5ZnO(CH2)2Br and Zn(0(CH2)2Br)2 were used by Jerome and co-workers for the controlled ROP of -CL (75). Well-defined single-site zinc-based catalysts, [(BDI-l)ZnO-i-C3H7)]2 (Fig. 14), convert j8-BL and -VL into high molecular weight poly(3-hydroxyalkanoates) (76). Moreover, ROP of (S,S-LA, rac-LA, and meso-IA leads to isotactic, heterotactic, and syndiotactic PIAs, respectively (77-79). 

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