Polymerization vinyl monomer

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). 

Because high temperatures are required to decompose diaLkyl peroxides at useful rates, P-scission of the resulting alkoxy radicals is more rapid and more extensive than for most other peroxide types. When methyl radicals are produced from alkoxy radicals, the diaLkyl peroxide precursors are very good initiators for cross-linking, grafting, and degradation reactions. When higher alkyl radicals such as ethyl radicals are produced, the diaLkyl peroxides are useful in vinyl monomer polymerizations. 

Peioxydicaibonates are efficient polymerization initiators for most vinyl monomer polymerizations, especially for monomers such as acrylates, ethylene, and vinyl chloride. They are particularly good initiators for less reactive monomers such as those containing aHyl groups. They are also effective for curing of unsaturated polyester mol ding resins. 

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. 

The first-order decomposition rates of alkyl peroxycarbamates are strongly influenced by stmcture, eg, electron-donating substituents on nitrogen increase the rate of decomposition, and some substituents increase sensitivity to induced decomposition (20). Alkyl peroxycarbamates have been used to initiate vinyl monomer polymerizations and to cure mbbers (244). They Hberate iodine quantitatively from hydriodic acid solutions. Decomposition products include carbon dioxide, hydrazo and azo compounds, amines, imines, and O-alkyUiydroxylarnines. Many peroxycarbamates are stable at ca 20°C but decompose rapidly and sometimes violently above 80°C (20,44). 

The main industrial use of alkyl peroxyesters is in the initiation of free-radical chain reactions, primarily for vinyl monomer polymerizations. Decomposition of unsymmetrical diperoxyesters, in which the two peroxyester functions decompose at different rates, results in the formation of polymers of enhanced molecular weights, presumably due to chain extension by sequential initiation (204). 

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). 

Vinyl monomers, polymerization of, 154 Vinyl polymerization, 172 Vinylidine, monomer polymerization of, 164... 

Uses. There are about forty to fifty organic peroxides commercially available in more than seventy formulations designed for specific applications which include (1) initiators for vinyl monomer polymerizations, and copolymerizations of monomers such as vinyl chloride, ethylene, styrene, vinyl acetate, acrylics, fluoroolefms and buta-dienestyrene (2) curing agents for thermoset polyesters, styrenated alkyds and oils, silicone rubbers and poly allyl diglycol carbonates ... 

Some of the vinyl monomers polymerized by transition metal benzyl compounds are listed in Table IX. In this table R represents the rate of polymerization in moles per liter per second M sec-1), [M]0 the initial monomer concentration in moles per liter (M) and [C]0 the initial concentration of catalyst in the same units. The ratio i2/[M]0[C]0 gives a measure of the reactivity of the system which is approximately independent of the concentration of catalyst and monomer. It will be observed that the substitution in the benzyl group is able to affect the polymerization rate significantly, but the groups that increase the polymerization rate toward ethylene have the opposite effect where styrene is concerned. It would also appear that titanium complexes are more active than zirconium. The results with styrene and p-bromostyrene suggests that substituents in the monomer, which increase the electronegative character of the double bond, reduces the polymerization rate. The order of reactivity of various olefinically unsaturated compounds is approximately as follows ... 

Table 1. Statistical copolymers of FOA with vinyl monomers. Polymerizations were conducted at 59.4 +0.1°C and 345 + 0.5 bar for 48 hours in C02. Intrinsic viscosities were determined in 1,1,2-trifluorotrichloroethane (Freon-113) at 30 °C [23]...

Whether a vinyl monomer polymerizes by radical, anionic, or cationic initiators depends on the inductive and resonance characteristics of the substituent(s) present. The effect of the... 

Dialkyl peroxydicarbonates are used primarily as free-radical initiators for vinyl monomer polymerizations. Dialkyl peroxydicarbonate decompositions are accelerated by certain metals, concentrated sulfuric acid, and amines. Violent decompositions can occur with neat or highly concentrated peroxides. 

The main industrial use of rert-alkyl peroxyesters is in the initiation of free-radical chain reactions, primarily for vinyl monomer polymerizations. 

In most vinyl monomer polymerizations measurable monomer concentrations at equilibrium are only apparent at elevated temperatures (T > 150°C). However, the corresponding concentrations of -methyl-styrene are measurable at room temperature. This is caused by the enthalpy of polymerization which is, compared with other monomers, relatively low (at a comparable entropy of polymerization). 

Kuran, W., Polar Vinyl Monomer Polymerization and Copolymerization with Olefins Promoted by Organometallic Catalysts , Polimery, 42, 604-609 (1997). 

Bamford et al. [157] were the first to observe the acceleration of vinyl monomer polymerization caused by inorganic salt addition. They polymerized acrylonitrile dissolved in dimethyl-formamide with 2,2 -azobisisobutyronitrile. The reaction rate was increased by the addition of LiCl. The observed effect was ascribed to the increase of the rate constant and interpreted by complex formation between lithium chloride and the nitrile group of the radical. 

Vinyl monomers polymerize by attack of an active center (4-5) on the double bond. Equation (4-1) represents head-to-tail enchainment ... 

Much more successful was the reaction of various monomers with bone, using the persulfate-bisulfite redox system as initiator in a carbon dioxide atmosphere. Over 10 acrylate and methacrylate and a few vinyl monomers polymerized on the substrate, some in nearly quantitative yield. Reaction times of 15 min were sufficient for grafting. The amount... 

For vinyl monomers polymerizing by a radical mechanism, Q, and e, are known (see Chap. 5, Table 3A). Therefore Q end can be determined by... 

Many applications of metal salts as photoinitiators have been described. These include (i) vinyl monomer polymerization using iron(m) salt-saccharide systems 1 (ii) mixtures of tetraphenylporphineiron(m), amine, and CC14 2... 

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