Vinyl monomers, reaction with

Zinc and cadmium alkyls have not been successful as stereospecific catalysts in the absence of co-catalysts, presumably because they do not complex strongly enough with the monomer and the metal-carbon bonds are too covalent. Cadmium alkyls were first reported by Furukawa and coworkers (260) to induce vinyl polymerization, but it was shown later (267, 262) that oxygen was a co-catalyst and the reactions were free radical in nature. Similar free radical results were obtained with zinc alkyls (261—263) and vinyl monomers. However, with more basic and more easily polarized monomers, such as olefin oxides and aldehydes, the zinc catalysts operate by a coordinated anionic mechanism (250). 

Another new route of synthesis for soluUe polymer supports based not on the usual polymer-analogous derivatization but on the preparation of the support by copolymerization of functional monomers was outlined and demonstrated by Geckeler and Bayer [73,104]. They used radical copolymerization of amino acid alkenyl esters, which are easily accessible by a vinyl exchange reaction with vinyl acetate, with l-vinyl-2-pyrrolidinone as solubilizing comonomer for direct preparation of a functional soluble support [104]. Thus, a carrier soluble in water as well as in many or nic solvents was obtained which already contained the first amino acid residue of the peptide ... 

Chain transfer reactions mostly proceed by abstraction of a monovalent atom such as hydrogen or a halogen. The scission of a bond carbon - oligovalent (e.g., H) atom is of interest for the introduction of endgroups into a polymer produced in a free radical reaction. Radically induced vinyl monomer polymerization with the possibility of chain transfer to a polymer of different chemical structure present in the reaction mixture leads to graft copolymers if bond scission occurs outside the main chain, no matter whether a single atom or a grouping is abstracted. Quite a different result is obtained if a radical attack involves a bond in the main chain of the polymer, if this bond scission occurs at a monovalent atom, which must be at the chain end, there is block copolymer formation. If bond scission occurs inside the polymer backbone, either block or random copolymers are produced [63]. 

Vinyl monomers react with dioxygen via the bimolecular reaction involving the double bond... 

The steps in free-radical initiated reactions of vinyl monomers (M) with cellulose (C) in solvent (S) to yield copolymers (CM), with a possible intermediate or sensitizing initiator (I), may be represented as follows, where an asterisk indicates activated state. 

The kinds of vinyl monomers which undergo anionic polymerization are those with electron-withdrawing substituents such as the nitrile, carboxyl, and phenyl groups. We represent the catalysts as AB in this discussion these are substances which break into a cation (A ) and an anion (B ) under the conditions of the reaction. In anionic polymerization it is the basic anion which adds across the double bond of the monomer to form the active center for polymerization ... 

Any discussion based on reactivity ratios is kinetic in origin and therefore reflects the mechanism or, more specifically, the transition state of a reaction The transition state for the addition of a vinyl monomer to a growing radical involves the formation of a partial bond between the two species, with a corre sponding reduction of the double-bond character of the vinyl group in the monomer ... 

In general, acryUc ester monomers copolymerize readily with each other or with most other types of vinyl monomers by free-radical processes. The relative ease of copolymerization for 1 1 mixtures of acrylate monomers with other common monomers is presented in Table 7. Values above 25 indicate that good copolymerization is expected. Low values can often be offset by a suitable adjustment in the proportion of comonomers or in the method of their introduction into the polymerization reaction (86). 

Wheieas the BPO—DMA ledox system works well for curing of unsaturated polyester blends, it is not a very effective system for initiating vinyl monomer polymerizations, and therefore it generally is not used in such appHcations (34). However, combinations of amines (eg, DMA) and acyl sulfonyl peroxides (eg, ACSP) are very effective initiator systems at 0°C for high conversion suspension polymerizations of vinyl chloride (35). BPO has also been used in combination with ferrous ammonium sulfate to initiate emulsion polymerizations of vinyl monomers via a redox reaction (36). 

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

The reactions of alkyl hydroperoxides with ferrous ion (eq. 11) generate alkoxy radicals. These free-radical initiator systems are used industrially for the emulsion polymerization and copolymerization of vinyl monomers, eg, butadiene—styrene. The use of hydroperoxides in the presence of transition-metal ions to synthesize a large variety of products has been reviewed (48,51). 

Without other alternatives, the carboxyalkyl radicals couple to form dibasic acids HOOC(CH)2 COOH. In addition, the carboxyalkyl radical can be used for other desired radical reactions, eg, hydrogen abstraction, vinyl monomer polymerization, addition of carbon monoxide, etc. The reactions of this radical with chloride and cyanide ions are used to produce amino acids and lactams employed in the manufacture of polyamides, eg, nylon. 

Etee-tadical reactions ate accompHshed using a variety of processes with different temperature requirements, eg, vinyl monomer polymerization and polymer modifications such as curing, cross-linking, and vis-breaking. Thus, the polymer industries ate offered many different, commercial, organic peroxides representing a broad range of decomposition temperatures, as shown in Table 17 (19,22,31). 

Because no molecule is spHt out, the molecular weight of the repeating unit is identical to that of the monomer. Vinyl monomers, H2C=CHR (Table 2) undergo addition polymerization to form many important and familiar polymers. Diene (two double bonds) monomers also undergo addition polymerization. Normally, one double bond remains, leaving an unsaturated polymer, with one double bond per repeating unit. These double bonds provide sites for subsequent reaction, eg, vulcanization. 

Formaldehyde reacts with the hydrogen on the a-carbon of the fatty acid from which the oxazoline was formed to yield a vinyl monomer which can be polymerized or utilized for synthesis (4). Thus, esters of the oxazoline formed from TRIS AMINO undergo the reaction... 

Polymerization and Spinning Solvent. Dimethyl sulfoxide is used as a solvent for the polymerization of acrylonitrile and other vinyl monomers, eg, methyl methacrylate and styrene (82,83). The low incidence of transfer from the growing chain to DMSO leads to high molecular weights. Copolymerization reactions of acrylonitrile with other vinyl monomers are also mn in DMSO. Monomer mixtures of acrylonitrile, styrene, vinyUdene chloride, methallylsulfonic acid, styrenesulfonic acid, etc, are polymerized in DMSO—water (84). In some cases, the fibers are spun from the reaction solutions into DMSO—water baths. 

Reaction of coke with calcium oxide gives calcium carbide, which on treatment with water produces acetylene. This was for many years an important starting point for the production of acrylonitrile, vinyl chloride, vinyl acetate and other vinyl monomers. Furthermore, during World War II, Reppe developed routes for many other monomers although these were not viable under normal economic conditions. 

Addition polymerisation is effected by the activation of the double bond of a vinyl monomer, thus enabling it to link up to other molecules. It has been shown that this reaction occurs in the form of a chain addition process with initiation, propagation and termination steps. 

Polymerization Exothermic reaction which, unless carefully controlled, can run-away and create a thermal explosion or vessel overpressurization Refer to Table 7.20 for common monomers Certain processes require polymerization of feedstock at high pressure, with associated hazards Many vinyl monomers (e.g. vinyl chloride, acrylonitrile) pose a chronic toxicity hazard Refer to Table 7.19 for basic precautions... 

Radical copolymerization is used in the manufacturing of random copolymers of acrylamide with vinyl monomers. Anionic copolymers are obtained by copolymerization of acrylamide with acrylic, methacrylic, maleic, fu-maric, styrenesulfonic, 2-acrylamide-2-methylpro-panesulfonic acids and its salts, etc., as well as by hydrolysis and sulfomethylation of polyacrylamide Cationic copolymers are obtained by copolymerization of acrylamide with jV-dialkylaminoalkyl acrylates and methacrylates, l,2-dimethyl-5-vinylpyridinum sulfate, etc. or by postreactions of polyacrylamide (the Mannich reaction and Hofmann degradation). Nonionic copolymers are obtained by copolymerization of acrylamide with acrylates, methacrylates, styrene derivatives, acrylonitrile, etc. Copolymerization methods are the same as the polymerization of acrylamide. 

A chain reaction polymerization of vinyl monomer, which is usually carried out by a photoinitiator to produce a primary radical (R ), which can interact with a monomer molecule (M) in a propagating process to form a polymer chain composed of a large number of monomer units (see Eq. [2] and reaction Scheme [3]. 

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