Zinc catalysts poly derivatives

However, there are numerous reported instances of stereocontrol by a site-control mechanism involving chiral metal catalysts. That is, Nozaki and coworkers first illustrated the asymmetric alternating copolymerization of cyclohexene oxide and CO2 employing a chiral zinc catalyst derived from an amino alcohol (Fig. 2a) [13-16]. This was soon followed by studies of Coates and coworkers utilizing an imine-oxazoline zinc catalyst (Fig. 2b) [17]. Both investigations provided isotactic poly(cyclohexene carbonate) (Fig. 3) with enantiomeric excess of approximately 70%. 

Preparation of Poly (propylene ether) Polyols. The polymerization of propylene oxide with zinc hexacyanocobaltate complexes in the presence of proton donors results in the production of low-molecular-weight polymers. Table V shows the variety of types of compounds that have been found to act this way. Since these compounds end up in the polymer chains, it seems reasonable to call them chain initiators. Thus, in essence, each of these compounds is activated by the catalyst to react with propylene oxide to form a hydroxylpropyl derivative. Thereafter, the reaction continues on the same basis, with the proton of the hydroxyl group reacting with further propylene oxide. This sequence is shown here with 1,5-pentanediol as the initiator. The hydroxyl... 

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerization is usually initiated by alkali hydroxides, especially potassium hydroxide. In the base-catalyzed polymerization of propylene oxide, some rearrangement occurs to give allyl alcohol. Further reaction of allyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly difunctional. By using zinc hexacyano cobaltate as catalyst, a more difunctional polyol is obtained (20). Olin has introduced the difunctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalyzed homopolymerization of tetrahydrofuran. Copolymers derived from tetrahydrofiiran and ethylene oxide are also produced. 

Thietane is a superior inhibitor of corrosion of iron in 10% hydrochloric acid and its effectiveness is said to be due to partial polymerization on the surface of the iron. Addition of chloride ion reduces the inhibition, possibly by inducing ringopening with the formation of sulfhydryl groups. The cyclic sulfide also has been considered as an odorant for natural gas and its absorption by organic soil and clay have been determined. Stabilization of methylchloroform and trichloroethylene by thietane, 2-methylthietane, 3-hydroxythietane, and two spirothietane derivatives has been claimed. Phosphorus and tin derivatives of 3,3-bis-hydroxy-methylthie-tane are reported to be light stabilizers for poly(vinyl chloride), and the dibutyl-tin derivative is a catalyst for the polymerization of aliphatic isocyanates. Mercury and zinc compounds derived from phenylmercury or phenylzinc hydroxide and 3-... 

Formaldehyde can be polymerized cationically to high-molecular-weight poly(oxymethylene) (catalysts BF3, HCIO4, etc. cf. the polymerization of trioxane), or anionically (tributylamine, triphenyl phosphine, diphenyl zinc, etc.), or by an insertion polymerization mechanism (aluminum isopropylate). Some anionic initiators, such as dimethylamine, induce a high proportion of the Cannizzaro reaction by-product, and thus there is a sharp decrease in the polymerization rate as the initiator concentration is increased. Extensive transfer reactions are occasionally observed in the cationic polymerizations. The transfer constant = KJkp has the value of 0.5-2.0 for low-molecular-weight acetals, 0.026 for methyl formate, and 0.(X)06 for halogen derivatives. 

The most widely-used catalysts for acetylation are sodium acetate and zinc chloride. With sodium acetate, the product is predominantly in the /J-form, except in the case of d- and L-arabinose, where the a-anomer is obtained. (By definition of the terms ot and / , -d- and a-L-arabinose are enantiomorphs.) Zinc chloride usually gives the a-acetyl derivative of the sugar, but D-glucosamine and D-galactosamine yield the jS-form with this catalyst. Of the other catalysts commonly employed, perchloric acid behaves like zinc chloride, whereas pyridine tends to give a mixture of the - and jS-poly-O-acetates. 

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