Azobis initiation

Such reactions can be initiated by free radicals, derived from compounds (initiators) such as benzoyl peroxide, ammonium persulphate or azobis-isobutyronitrile or by ionic mechanisms... 

DIITIATORS - FREE-RADICAL INITIATORS] (Voll4) l,ly-Azobis(cyanocyclohexane) [2094-98-6]... 

There has also been a trend in recent years to the use of free-radical initiators that decompose more rapidly than the traditional initiators such as caproyl and lauryl peroxides. Currently used initiators include peroxydicarbonates, t-butylperpiva-late, azobis-(2,4-dimethylvaleronitrile) and acetyl cyclohexylsulphonyl peroxide. 

Azo compounds having functional groups that stabilize the radical products are especially reactive. The stabilizing effect of the cyano substituent is responsible for the easy decomposition of azobis(isobutyronitrile) (AIBN), which is frequently used as a radical initiator. 

In another study, uniform composite polymethyl-methacrylate/polystyrene (PMMA/PS) composite particles in the size range of 1-10 fim were prepared by the seeded emulsion polymerization of styrene [121]. The PMMA seed particles were initially prepared by the dispersion polymerization of MMA by using AIBN as the initiator. In this polymerization, poly(7V-vinyl pyrolli-done) and methyl tricaprylyl ammonium chloride were used as the stabilizer and the costabilizer, respectively, in the methanol medium. Seed particles were swollen with styrene monomer in a medium comprised of seed particles, styrene, water, poly(7V-vinyl pyrollidone), Polywet KX-3 and aeorosol MA emulsifiers, sodium bicarbonate, hydroquinone inhibitor, and azobis(2-methylbu-... 

Interfacial polycondensation between a diacid chloride and hexamethylenediamine in the presence of small amounts of ACPC also yield polymeric azoamid, which is a macroazo initiator.[27] In this manner, azodicarbox-ylate-functional polystyrene [28], macroazonitriles from 4,4 -azobis(4-cyano-n-pentanoyl) with diisocyanate of polyalkylene oxide [29], polymeric azo initiators with pendent azo groups [3] and polybutadiene macroazoinitiator [30] are macroazoinitiators that prepare block and graft copolymers. 

The carboxyl terminated ACPA, 4,4 -azobis-(4-cya-nopentanoic acid), turned out to be a suitable reagent in condensation reactions. This compound can be prepared by Strecker s synthesis from levulinic acid following the method of Haines and Waters [12]. Regarding the formation of polymeric azo initiators, Matsakuwa et al. [13] reported on the condensation of ACPA with various diols and diamines in the presence of a condensation agent, I-methyl-2-chlorpyridinium iodide, and a cata-... 

Both S polymerization initiated by AlBMe176 180 (i.e. PS + 4) and MMA polymerization initiated by 1 J -azobis-l-phenylethane176 (i.e. PMMA + 1-phenylethyl radical) are reported lo give predominantly combination. Ito,7e has concluded that cross termination is not particularly favored over homotermination in S-MMA copolymerization. 

The radical alkylation of ketones is achieved by their conversion into the desired N-silyloxy enamines 81 (Scheme 13). The reaction of 81 with diethyl bromomalonate in the presence of EtsB (0.5 equiv) in benzene was performed in open air and stirred at room temperature for 3h. With nitro compounds it is achieved by their conversion into the desired ]V-bis(silyloxy)enamines (82) (Scheme 13). When the reaction is carried out with 82 and alkyl iodides with an electron-withdrawing substituent at the a-position, using V-70 as radical initiator (2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile)), it underwent a clean radical alkylation reaction to yield an oxime ether. Successful radical alkylation of... 

Skinner, W. A. Vitamin E oxidation with free radical initiators Azobis(isobutyronitrile). Biochem. Biophys. Res. Commurt. 1964, 15, 469 472. 

When aqueous solutions of the polymerisation initiators 2,2/-azobis(2-amidinio-propane) chloride and sodium peroxodisulfate are mixed, the title compound separates as a water insoluble shock-sensitive salt. The shock-sensitivity increases as the moisture level decreases, and is comparable with that of lead azide. Stringent measures should be used to prevent contact of the solutions outside the polymerisation environment. (The instability derives from the high nitrogen (21.4%) and oxygen (31.6%) contents, and substantial oxygen balance, as well as the structural factors present in the salt.)... 

RAFT polymerization of two anionic acrylamido monomers sodium 2-acrylamido-2-methylpropane-sulfonate, AMPS, and sodium 3-acrylamido-3-methyl-butanoate, AMBA, (Scheme 29) was conducted in water at 70 °C using 4,4/-azobis(4-cyanopentanoic acid) as the initiator and 4-cyanopentanoic acid dithiobenzoate as the RAFT chain transfer agent [80]. The synthesis was initiated either from one monomer or the other leading to narrow molecular weight distributions in both cases (Mw/Mn < 1.2). 

Monofunctional and difunctional xanthates, shown in Scheme 30, were employed as chain transfer agents in the synthesis of block and triblock copolymers of acrylic acid, AA and acrylamide, AAm PAA-fr-PAAm, PAAm-fr-PAA-fo-PAAm and P(AA-sfaf-AAm)-fr-PAAm [81]. The polymerizations were conducted in aqueous solutions at 70 °C with 4,4 -azobis(4-cyanopentanoic acid) as the initiator. The yields were almost quantitative,... 

Free radical polymerization combined with anionic ring polymerization was employed for the synthesis of poly(N-vinylpyrrolidone)-fr-poly(D,L-lactide), PVP-fr-PDLLA, as shown in Scheme 49 [121]. The free radical polymerization of VP was conducted using 2,2/-azobis[2-methyl-M-(2-hydroxyethyl)propionamide] as the initiator, isopropyl alcohol and 2-... 

Meso- and (+ )-azobis[6-(6-cyanododecanoic acid)] were synthesized by Porter et al. (1983) as an amphipathic free radical initiator that could deliver the radical center to a bilayer structure controllably for the study of free radical processes in membranes. The decomposition pathways of the diazenes are illustrated in Fig. 36. When the initiator was decomposed in a DPPC multilamellar vesicle matrix, the diazenes showed stereo-retention yielding unprecedented diastereomeric excesses, as high as 70%, in the recombination of the radicals to form meso- and (+ )-succinodinitriles (Brittain et al., 1984). When the methyl esters of the diazene surfactants were decomposed in a chlorobenzene solution, poor diastereoselectivity was observed, diastereomeric excesses of 2.6% and 7.4% for meso- and ( )-isomers respectively, which is typical of free radical processes in isotropic media (Greene et al, 1970). 

In this section, we review the properties of a series of PNIPAM-b-PEO copolymers with PEO blocks of varying length, with respect to the PNIPAM block. Key features of their solutions will be compared with those of PNIPAM-g-PEO solutions. PNIPAM-b-PEO copolymers were prepared by free-radical polymerisation of NIPAM initiated by macroazoinitiators having PEO chains linked symmetrically at each end of a 2,2/-azobis(isobutyronitrile) derivative [169,170]. The polydispersities of PEOs were low, enabling calculations of the number-average molar mass for each PNIPAM block from analysis of their H-NMR spectra (Table 2). 

The EtsSiH/tetracyanoethylene combination reduces acetals and ketals to the corresponding ethers but the yields are mixed.500 The full reduction of benz-aldehyde acetals to the toluene derivatives is realized by the initial reduction with Et3SiH/SnBr2-AcBr followed by Bu3SnH/AIBN (azobis(isobutyronitrile)) or LiAlH4.479 The overall yields are excellent. 

By using lipophilic initiators, such as 2,2 -azobis(isobutyronitrile) (AIBN), in the micro-ECP, diffusion of monomers is too slow compared with the reaction rate. Therefore, copolymerization is confined to the incoherent, lipophilic phase [112,113] and very small microgel particles with a rather uniform size result. 

Semitelechelic HPMA polymers were synthesized by free radical polymerization of HPMA using 2,2 -azobis(isobutyronitrile) (AIBN) as the initiator and alkyl mercaptans as chain transfer agents. Alkyl mercaptans with different functional groups, namely, 2-mercaptoethylamine, 3-mercapto-propionic acid, 3-mercaptopropionic hydrazide, and methyl 3-mercapto-propionate, were used as the chain transfer agents ST HPMA polymers... 

---