Ethylene derivatives addition polymerization

Despite the drawbacks of this method, it has been used to prepare a tremendous number of polypeptide hybrid block copolymers (Table 1), and when carefully executed provides reasonably well-defined samples. Synthetic polymer domains have been prepared by addition polymerization of conventional vinyl monomers, such as styrene and butadiene, as well as by ringopening polymerization in the cases of ethylene oxide and e-caprolactone. The generality of this approach allows NCA polymerization off of virtually any primary amine functionality, which was exploited in the preparation of star block copolymers by polymerization of sarcosine NCA from an amine-terminated trimethyleneimine dendritic core [37]. In most examples, the polypeptide domain was based on derivatives of either lysine or glutamate, since these form a-helical polypeptides with good solubility characteristics. These residues are also desirable since, when deprotected, they give polypep-... 

Ethylene Derivatives that Undergo Addition Polymerization... 

Mer is derived from the Greek word meros meaning part. Therefore, a monomer means one part or one unit dimer means two units oligomer means a few units and polymer means many units. A polymerization involves the reaction of a monomer to connect many monomer units. If the reaction is additive, where one monomer adds to the next as in the polymerization of styrene, the polymer is called an addition polymer. Polymerizations of olefins, such as ethylene, propylene, vinyl chloride, or styrene, are addition polymerizations. In an addition polymer, all of the atoms of the monomer remain in the polymer. If the monomers are connected in a condensation reaction such as when a carboxylic acid and an alcohol react to remove water and form an ester linkage, then the polymer is called a condensation polymer. Recognize that in this type of polymer all of the monomer atoms are not incorporated into the final polymer. 

Perhaps the most familiar addition polymer is polyethylene, a solid derived from the monomer ethylene. We might represent the polymerization process as... 

NbBrs, and NbCls-Pl Sn evidently proceeds via cyclotrimerization of diynes, which most probably involve cyclic carbometallation, details are not very clear.246 2463 Related reactions of Ta and Mo complexes were also investigated in this study. Formation of tantallacyclopropenes by complexation of alkynes with Ta complexes has also been reported247 (Scheme 51). In addition to the Ta-catalyzed polymerization of diynes mentioned above, Ta-catalyzed or -promoted cyclotrimerization reactions of alkynes to produce benzene derivatives, a Ta-promoted ethylene... 

The silica-supported chromate can be activated directly to a very efficient ethylene polymerization catalyst by ethylene itself or by reduction under CO, to yield active Cr(ll) bisiloxy species, ](=SiO)2Cr] [8]. While the silsesquioxane Cr derivative on its own does not lead to an active polymerization catalyst under ethylene (albeit only low ethylene pressure were tested), the silsesquioxane chromate ester can yield an active polymerization catalyst by addition of methyl-aluminoxane as co-catalyst. Comparison between the two catalytic systems is therefore possible but suffers from the lack of molecular definition of the active homogeneous species obtained after activation with the alkylating agent (Scheme 14.11). 

The first results of anionic polymerization (the polymerization of 1,3-butadiene and isoprene induced by sodium and potassium) appeared in the literature in the early twentieth century.168,169 It was not until the pioneering work of Ziegler170 and Szwarc,171 however, that the real nature of the reaction was understood. Styrene derivatives and conjugated dienes are the most suitable unsaturated hydrocarbons for anionic polymerization. They are sufficiently electrophilic toward carbanionic centers and able to form stable carbanions on initiation. Simple alkenes (ethylene, propylene) do not undergo anionic polymerization and form only oligomers. Initiation is achieved by nucleophilic addition of organometallic compounds or via electron transfer reactions. Hydrocarbons (cylohexane, benzene) and ethers (diethyl ether, THF) are usually applied as the solvent in anionic polymerizations. 

Nonionic Surface-Active Agents. Approximately 14% of the ethylene oxide consumed in the United States is used in the manufacture of nonionic surfactants. These are derived by addition of ethylene oxide to fatty alcohols, alkylphenols (qv), tall oil, alkyl mercaptans, and various polyols such as polypropylene glycol), sorbitol, mannitol, and cellulose. They are used in household detergent formulations, industrial surfactant applications, in emulsion polymerization, textiles, paper manufacturing and recycling, and for many other applications (281). 

A similar synthetic route was adopted by Stadler et al. for the synthesis of (PS)(PB)(PMMA) stars [54] as shown in Scheme 21. Living PS chains were end-capped with l-(4-bromomethylphenyl)-l-phenyl ethylene to produce the macromonomer. The capping reaction with DPE was employed in order to reduce the reactivity of the PSLi chain ends thus avoiding several side reactions (trans-metallation, addition to the double bond of the DPE derivative). The next step involved the linking of living PB chains, prepared in THF at -10 °C to the end double bond of the macromonomer. This produces a new active center which was used to initiate the polymerization of MMA leading to the formation of the desired product. 

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. 

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