Optically active hydrocarbons polymerizations

Cyclopolymerization of 1,5-hexadienes Oligomerization to Optically Active Hydrocarbons Polymerization in the Presence of Filling Materials... 

Not only polyethylene can be synthesized, but also many kinds of copolymers and elastomers, new structures of polypropylenes, polymers and copolymers of cyclic olefins. In addition, polymerization can be performed in the presence of fillers and oligomerization to optically active hydrocarbons is possible. For recent reviews and books see [17-20]. 

The hydrocarbons of the composition (CsHs) present in plants are called terpenes. The more important members of the class have the formula CioHie, and are obtained from the sap of coniferous trees and from fruits of the citrus variety they are the principal constituents of oil of turpentine and of many essential oils. With few exceptions the terpenes are liquids some are optically active. They polymerize when treated with sulphuric acid, and form addition-products with bromine, hydrochloric acid, and water. The terpenes can be converted into cymene, and like this hydrocarbon yield p-toluic acid and terephthalic acid when oxidized. 

Towards the end of the second millennium, studies of the transition elements continued to make major contributions to chemical science and technology. The development of new catalysts and reagents represents one area of activity. Examples are provided by the activation of saturated hydrocarbons by rhodium or lutetium complexes, new syntheses of optically active products in reactions which employ chiral metal compounds, and transition metal compounds which catalyse the stereospecific polymerization of alkenes. The ability of transition metal centres to bind to several organic molecules has been exploited in the construction of new two- and three-dimensional molecular architectures (Figure 1.4). New materials containing transition elements are being developed, one... 

Very little information is available on the polymerization ofO.A. butadiene derivatives, in contrast with the asymmetric polymerization of diene hydrocarbons, like trans-1,3-pentadiene, in the presence of an optically active complex catalyst in heterogenous phase, (see ref. [4] and Part 11(1)) subsequently carried out by G. Natta and coworkers. 

Abstract. The methods are discussed for the synthesis of optically active polymers with a hydrocarbon backbone starting with unsaturated monomers. Emphasis is given to the stereochemistry of the polymerization process and the cases are considered yielding directly an optically active polymer or a polymer separable in samples having detectable optical activity. 

In conclusion, several methods are now at the disposal of the chemist which permit him to prepare optically active polymers with a hydrocarbon backbone and a great deal of structure and properties. Future work in this area should be mainly devoted to the attainment of optically active catalytic systems able to select with high specificity one enantiomer from a racemic mixture or to give a high asymmetric induction in the polymerization of prochiral compounds. 

The Pd clusters have been produced by a recently developed high-frequency laser evaporation source, ionized, then guided by ion optics through differentially pumped vacuum chambers and size-selected by a quadrupole mass spectrometer [16-18]. The monodispersed clusters have been deposited with low kinetic energy (0.1-2 eV) onto a MgO thin film surface. The clusters-assembled materials obtained in this way exhibit peculiar activity and selectivity in the polymerization of acetylene to form benzene and aliphatic hydrocarbons [30]. 

Biopolymers are polymers formed in nature during the growth cycles of all organisms hence, they are also referred to as natural polymers. The biopolymers of interest in this review are those that serve in nature as either structural or reserve cellular materials. Their syntheses always involve enzyme-catalyzed, chain-growth polymerization reactions of activated monomers, which are generally formed within the cells by complex metabolic processes. The most prevalent structural and reserve biopolymers are the polysaccharides, of which many different types exist, but several other more limited types of polymers exist in nature which serve these roles and are of particular interest for materials applications. The latter include the polyesters and proteins produced by bacteria and the hydrocarbon elastomers produced by plants (e.g. natural rubber). In almost all cases (natural rubber is an exception), all of the repeating units of these biopolymers contain one or more chiral centers and the repeating units are always present in optically pure form that is, biopolymers with asymmetric centers are always 100% isotactic. 

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