Vinyl monomers polymeric radical

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. 

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 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). 

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... 

Here we discuss dispersion polymerizations that are not related to vinyl monomers and radical polymerization. The first one is the ring-opening polymerization of e-caprolactone in dioxane-heptane (30). A graft copolymer, poly(dodecyl acrylate)-g-poly(e-caprolactone), is used as a stabilizer. The polymerization proceeds via anionic or pseudoanionic mechanism initiated by diethylaluminum ethoxide or other catalysts. The size of poly(caprolactone) particles depends on the composition of stabilizer, ranging from 0.5 to 5 i,m. Lactide was also polymerized in a similar way. Poly(caprolactone) and poly(lactide) particles with a narrow size distribution are expected to be applied as degradable carriers of drugs and bioactive compounds. 

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. 

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. 

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... 

Otsu, T. Structure and Reactivity of Vinyl Monomers in Radical Polymerization. In ... 

A useful scheme was proposed by Alfrey and Price (1947) to provide a quantitative description of the behavior of vinyl monomers in radical polymerization, in terms of two parameters for eac/t monomer rather than for a monomer pair. These parameters are denoted by Q and e and the method is known as the O - e scheme. An advantage of the method is that it allows calculation of monomer reactivity ratios ri and T2 from the same Q and e values of the monomers irrespective of which monomer pair is used. The scheme assumes that each radical or monomer can be classified according to its reactivity (or resonance effect) and its polarity so that the rate constant for a radical-monomer reaction, e.g., the reaction of Mi ° radical with M2 monomer, can be written as... 

Vinyl monomer polymerization has been photoinitiated with quaternary ammonium salts, an example of the mechanism of which is given in reaction (4), the benzoyl radical being the initiating species.12... 

The values of the copolymerization constants (ri= 1,49 0,01, V2 =0,45 0,002) indicate that the MCM is a less-active monomer in copolymerization than styrene. Note the large negative e value of-1.4. For common vinyl monomers polymerizing by a radical mechanism e is equal to -1 to 1.5. Since this parameter characterizes a polarity measure of the substituent at the double bond the correlation of e and its Hammet s constant (a ) [110] for the monomers CH2=CHX is observed (Fig. 4-10). 

In this cormection, systematic stndies were made of the inhibiting effect of many stable mono and poly radicals on the kinetics and mechanism of vinyl monomer polymerization. The efCtiency of nitroxyls as free radical acceptors has promoted their usage to explore the mechanism of polymerization by means of the inhibition technique. Usually, nitroxyls have time to only react with a part of the radicals formed at... 

Diacyl peroxides are used in a broad spectrum of applications, including curing of unsaturated polyester resin compositions, cross-linking of elastomers, production of poly(vinyl chloride), polystyrene, and polyacrylates, and in many non-polymeric addition reactions. The activities of acyloxy radicals in vinyl monomer polymerization (79,80) and imder high-pressure conditions (81,82) have been investigated. 

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]. 

The first type of hydrocarbon membrane for fuel cell applications was the sulfonated polystyrene-divinylbenzene co-polymer membranes equipped for the power source in NASA s Gemini space flights, but the sulfonated polystyrene had low chemical stability for long-term applications, because the proton on the tertiary carbons and benzylic bonds are easily dissociated in an oxygen environment forming hydroperoxide radicals. Since a styrene monomer is easily co-polymerized with other vinyl monomers via radical polymerization methods, various styrenic polymers were researched intensively. Two commercial polystyrene-based/related membranes are available BAM (Ballard), and Dais Analytic s sulfonated styrene-ethylene-butylene-styrene (SEBS) membrane. Dais membranes are produced using... 

Vinyl monomers polymerize by y-ray and electron beams that are higher in energy than visible radiation [12, 13]. Although it is possible to observe ionic polymerization, the majority of cases are by a free radical mechanism. It is possible to obtain homogeneous gels because (1) it is unnecessary to use a free radical initiator or catalyst (2) the reaction... 

Another current trend in controlled radical ROP is the utilization of reversible addition-fragmentation chain transfer (RAFT), which has been widely exploited as a powerful tool to control radical polymerizations of various vinyl monomers. The radical ROPs of 5,6-benzo-2-methylene-l,3-dioxepane, a seven-membered cyclic ketene acetal, and those of 9,10-dihydroanthracene derivatives bearing exo-methylene and cyclopropane moieties have been reported. 

---