Stereoregular, synthesis

Kohnke F. H., Mathias J. P., Stoddart J. F. Substrate-Directed Synthesis the Rapid Assembly of Novel MacropolycycUc Structures Via Stereoregular Diels-Alder Oligomerizations Top. Curr. Chem. 1993 165 1 69... 

Topochemical [24-2] photoreactions of diolehn crystals has been reviewed. The reactions clearly depart from typical solution chemistry crystal-lattice control offers a unique synthetic route into photodegradable polymers, highly strained [24-2] paracyclophanes, stereoregular polymers, and absolute asymmetric synthesis. However, achieving the desired type of crystal... 

Kohnke, F.H., Mathias, J.P., and Stoddart, J.F. Substrate-Directed Synthesis The Rapid Assembly of Novel Macropolycyclic Structures via Stereoregular Diels-Alder Oligomerizations. 165, 1-69 (1993). 

The architecture of macromolecules is another important synthetic variable. New materials with controlled branching sequences or stereoregularity provide tremendous opportunity for development. New polymerization catalysts and initiators for controlled free-radical polymerization are driving many new materials design, synthesis, and production capabilities. Combined with state-of-the-art characterization by probe microscopy, radiation scattering, and spectroscopy, the field of polymer science is poised for explosive development of novel and important materials. New classes of nonlinear structured polymeric materials have been invented, such as dendrimers. These structures have regularly spaced branch points beginning from a central point—like branches from a tree trunk. New struc-... 

Ewen was the first to report the synthesis of stereoregular propene polymers with soluble Group 4 metal complexes and alumoxane as the co-catalyst [13], He found that Cp2TiPh2 with alumoxane and propene gives isotactic polypropene. This catalyst does not contain an asymmetric site that would be able to control the stereoregularity. A stereo-block-polymer is obtained, see Figure 10.6. Formation of this sequence of regular blocks is taken as a proof for the chain-end control mechanism. 

He was a Professor of Industrial Chemistry, School of Engineering, Polytechnic Institute of Milan, Milan, Italy since 1937. He became involved with applied research, which led to the production of synthetic rubber in Italy, at the Institute in 1938. He was also interested in the synthesis of petrochemicals such as butadiene and, later, oxo alcohols. At the same time he made important contributions to the understanding of the kinetics of some catalytic processes in both the heterogeneous (methanol synthesis) and homogeneous (oxosynthesis) phase. In 1950, as a result of his interest in petrochemistry, he initiated the research on the use of simple olefins for the synthesis of high polymers. This work led to the discovery, in 1954, of stereospecific polymerization. In this type of polymerization nonsymmetric monomers (e.g., propylene, 1-butene, etc.) produce linear high polymers with a stereoregular structure. 

SYNTHESIS OF LINEAR AND HYPERBRANCHED STEREOREGULAR AMINOPOLYSACCHARIDES BY OXAZOLINE GLYCOSYLATION... 

Synthesis of Linear and Hyperbranched Stereoregular Aminopolysaccharides by Oxazoline Glycosylation... 

Synthesis of natural-type aminopolysaccharide having dibenzylchitin structure was achieved by the polymerization of a sugar oxazoline monomer, 1 having one hydroxy group at position 4 (Scheme 4) [9]. The polymerization was carried out with an acid catalyst in 1,2-dichloroethane solvent at reflux temperature. All the H-NMR, C-NMR, and IR spectra as well as elemental analysis data of the isolated polysaccharide supported that the polymerization proceeded by the stereoregular glycosylation to give (1 4)-... 

Several asymmetric polymerization of small molecules have been reported applying the asymmetric catalysis methodology to polymer synthesis. Unique physical properties due to the mainchain stereoregularity are envisioned. 

Wullf and Hohn recently described several new stereochemical results (93). They reported the synthesis of a copolymer between a substituted styrene (M ) and methyl methaciylate (M2) having, at least in part, regular. . . M,M M2M MiM2. . . sequences. Polymerization involves the use of a chiral template to which the styrene monomer is loosely bound. After elimination of the template, the polymer shows notable optical activity that must be ascribed to the presence of a chiral stmcture similar to that shown in 53 (here and in other formulas methylene groups are omitted when unnecessaiy for stereochemical information). This constitutes the first stereoregular macromolecular compound having a three monomer unit periodicity. 

Asymmetric induction and stereoregularity can be treated, at least in part, as two distinct phenomena however, it has been observed that the values of pu and Pol can be divided into two parts one dependent on chiral factors external to the chain (catalyst, environment, etc.) and the other dependent on the intramolecular chain induction. This latter is a factor of stereoregularity or cooper-ativity rather than of chirality (its value is identical for both the DD and LL successions) (328). Both factors can be expressed as differences of free energies of activation In favorable cases, when they are of the same sign, asymmetric polymerization becomes easier (i.e., under the same conditions it gives a higher optical yield) than an analogous nonmacromolecular asymmetric synthesis. 

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