Polymerization stereospedfic

Stereospedfic Polymerization of Styrene with Ziegler-Natta-Catalysts... 

The process of stereospedfic polymerization is that in which, by the aid of a catalyst or an initiator, each propagation reaction is controlled structurally and stereochemically to only one direction. In this sense, each propagation reaction can be compared to the reaction of a low molecular weight compound. 

Full understanding of the stereospecific polymerization, especially of the asymmetric one, is one of the most fascinating problems in synthetic organic chemistry as well as in synthetic polymer chemistry. Requirement posed on the stereospedfic polymerization may be severer than that on the stereospedfic reaction of low molecular wdght compound, because any side reaction, if occurred, puts the structurally and stereochemically irregular units, which cannot be separated from the regular one, in the polymer molecule. 

All these organometallic compounds, except for [V], were isolated in pure crystalline state. The stereospedfic polymerization of acetaldehyde was catalyzed by [I] to [IV], and that of propylene oxide by [V] to [VIII]. The crystalline organometallic compound is superior to the liquid one for our purpose, because the former can be purified more easily and extensively than the latter in a small scale operation. 

The AlR3-acid amide (1 1) catalyst system thus proved to be an excellent catalyst for the stereospedfic polymerization of acetaldehyde and to be far superior to the AlR3-ketone (1 1) catalyst system. Both linear and cyclic acid amides gave a similar degree of stereospecificity with good reproducibility (35). We considered that the former catalyst system would be more suitable for our purpose, because this type of... 

In order to find a highly stereospedfic, homogeneous catalyst for the polymerization of propylene oxide, we selected the organometallic compound-primary amine catalyst system which exhibited excellent stereospecificity in the polymerization of acetaldehyde. 

Results of the polymerization of propylene oxide by these four kinds of organometallic compounds showed that the zinc compounds are superior to the aluminum compounds with respect to their stereoregulating power. It is noteworthy that the zinc catalyst is generally superior to the aluminum catalyst as the stereospedfic polymerization catalyst. Among the two organozinc compounds, EtZnNBu ZnEt was thought to be more suitable than EtZnNHBu for detailed studies, because the former was monomeric and had no reactive hydrogen atom. 

Yasuda,H, Fujita,K Yamamoto,S, Tani,H. Stereospedfic polymerization of acetaldehyde by diethylaluminum butoxides. J. Polymer Sci. A-l to be published. 

Oguni,N. Stereospedfic polymerization of acetaldehyde using RjAl-NR"-AJR2 and Li+[R3AJ-NR -A1R2]- as catalysts. J. Polymer Sd. B3,123 (1965)... 

Yasuda.H. Stereospedfic polymerization of acetaldehyde by R2A10CR NPh active spedes and essential role of cocatalyst J. Polymer Sd. B 7,17 (1969). 

Yasuda,H., Araki.T., Tani,H. Structure and chemical behavior of an organoaluminum [R2A10CR NPh]2. A stereospedfic catalyst for polymerization of acetaldehyde. J. Organomatal. Chem. in press. 

Tani,H. Stereospedfic polymerization of aliphatic monoaldehyde. Macromolecules, in press. 

Oguni,N., Tani,H. Nitrogen-containing organozinc and organoaluminum as catalyst for stereospedfic polymerization of propylene oxide (in preparation). 

First of all we shall examine the preparation and properties of optically active polymers subsequently we shall briefly discuss the contribution given by the research on optically active polymers to the investigation on the stereospedfic polymerization and on the conformation of macromolecules in solution. 

RESINS (Acrylonitrile-Butadiene-Styrene). Commonly referred to as ABS resins, these materials are thermoplastic resins which are produced by grafting styrene and acrylonitrile onto a diene-rubber backbone. The usually preferred substrate is polybutadiene because of its low glass-transition temperature (approximately —80°C). Where ABS resin is prepared by suspension or mass polymerization methods, stereospedfic diene rubber made by solution polymerization is the preferred diene. Otherwise, the diene used is a high-gel or cross-linked latex made by a hot emulsion process. 

The first stereospedfic synthesis of a linear polysaccharide containing only (1 ->6)-linked ot-D-glucopyranosyl residues was achieved as early as 1961 by ring-opening polymerization of l,6-anhydro-2,3,4-tri-0-methyl-P-i>glucopyra-... 

This part of the review has stressed the importance of the electrophilic character of the cation and the role of surfaces in stereospedfic coordinated polymerizations of non-polar monomers. The same factors hold generally for polar monomers with two important differences. The catalyst coordinates with electron pairs on the electro-negative atoms rather than with the jr-electrons of the unsaturation. Furthermore, surfaces are not essential because the electronegative groups can provide the additional points of attachment needed for consistent spatial orientation relative to the chain end. 

Yuki, H. and Hatada, K. Stereospedfic Polymerization of Alpha-Substituted Acrylic Acid Esters. Vol. 31, pp. 1-45. 

The increase in isotacticity seems to be essentially connected to the decrease of the initial rate, as practically no change in the isotacticity index with polymerization time was detected. Moreover, while the atactic productivity decreases monotonically with the EB/TEA ratio in both systems, the isotactic productivity has a more complex behavior with the binary catalyst it remains almost unchanged up to EB/TEA s 0.25 and then falls, whereas with the ternary catalyst it increases up to EB/TEA 0.2 and then rapidly drops. On the grounds of these results, Spitz suggested that the reversible adsorption on the catalytic surface of the TEA EB complex (which is supposed to be very fast) changes the non specific centers into stereospedfic, though less active, centers, while the slower adsorption of free EB reversibly poisons both types of sites. The differences between the binary and the ternary catalysts would arise mainly from the presence, in the latter, of a larger number of potential stereospecific sites. 

Monakov YB, Marina NG, Sabirov ZM (1994) Polym Sci USSR (Engl. Trans.) 36 1404 Taube R, Sylvester G, (1996) Stereospedfic polymerization of butadiene or isoprene. In Comils B, Herrmann WA (eds) Applied homogeneous catalysis with organometallic compounds, vol. 1 VCH, Weinheim, p 280... 

In the opinion of the author, the proc of light al rption by an atom or a molecule is a good model for stereospecific polymerization in the above sense. Only a few tranations among all possible tranations in an atom or a molecule are spectrally active. Similarly, only some possible microstructures are formed in stereospedfic polymerizations. 

FIGURE 1.5 Bimetallic mechanism for stereospedfic polymerization. (Adapted from Patat, E and Sinn, H. 1958. Angew. Ghent., 70, 496.)... 

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