Initiators azobisisobutyronitrile

Compounds with active hydrogen add to the carbonyl group of acetone, often followed by the condensation of another molecule of the addend or loss of water. Hydrogen sulfide forms hexamethyl-l,3,5-trithiane probably through the transitory intermediate thioacetone which readily trimerizes. Hydrogen cyanide forms acetone cyanohydrin [75-86-5] (CH2)2C(OH)CN, which is further processed to methacrylates. Ammonia and hydrogen cyanide give (CH2)2C(NH2)CN [19355-69-2] ix.orn. 6<55i the widely used polymerization initiator, azobisisobutyronitrile [78-67-1] is made (4). 

It is important to emphasize that the hydroxy dithioketal cyclization can be conducted under mild reaction conditions and can be successfully applied to a variety of substrates.15 However, the utility of this method for the synthesis of didehydrooxocane-contain-ing natural products requires the diastereoselective, reductive removal of the ethylthio group. Gratifyingly, treatment of 13 with triphenyltin hydride and a catalytic amount of the radical initiator, azobisisobutyronitrile (AIBN), accomplishes a homolytic cleavage of the C-S bond and furnishes didehydrooxocane 14 in diastereo-merically pure form (95 % yield), after hydrogen atom transfer. 

A plot of the initial reaction rate versus concentration, on logarithmic scales. The reaction is the polymerization of methyl methacrylate, and the concentration is that of the initiator, azobisisobutyronitrile. The slope is 0.496, showing that the reaction is half-order with respect to the initiator concentration. 

Driscoll [67], Lorimer and Mason [79] and Price [65[ have also obtained inverse Arrhenius temperature dependencies for reactions performed in the presence of ultrasound. For example Driscoll has investigated the polymerisation of styrene and methyl methacrylate in the presence of their respective homopolymers and observed that the lower the reaction temperature the faster was the reaction rate and the higher the final polymer yield (Figs. 5.38 and 5.39). Price on the other hand using a non polymer system has sonicated methyl butyrate (MeOBu) and compared the rates of radical production in the absence and presence of the initiator azobisisobutyronitrile (AIBN) (Tab. 5.18). 

Initiator Azobisisobutyronitrile (Wako Pure Chemical Industries, Ltd, Osaka, Japan). Store at 4°C. 

The use of a focused infrared laser beam on a surface results in local heating, which has been applied to synthesize MIPs locally by thermal polymerization [72]. In this case, a common thermo-initiator, azobisisobutyronitrile, was used together with a standard MIP recipe, to generate MIP microdots in a microfluidic device. 

A typical procedure for the preparation of a concentrated emulsion is as follows. A small amount of an aqueous solution containing sodium dodecyl-sulfate (SDS) was placed in a single neck flask (100 ml capacity) equipped with a mechanical stirrer. Styrene containing the initiator Azobisisobutyronitrile (AIBN) was added to the aqueous solution, with stirring. The whole preparation process of the concentrated emulsion lasted for 10-15 min at room temperature. 

By carrying out one experiment, changes of monomer and polymer and also of the initiator (azobisisobutyronitrile) are reflected in the NIR and the IR, respectively. Quantitative analysis is largely facilitated by the appearance of characteristic non-overlapping bands. On the other hand, computer programs for band separation are available. In addition, the integration of molar absorption coefficients to yield concentrations need not extend over entire bands, but may be performed over half bands or even over suitable band sections. 

That a typical free radical initiator, azobisisobutyronitrile, would also catalyze this process was demonstrated by Walling and Rabinowitz (299,300), who proposed direct reaction of thiyl radicals on phosphite to yield an intermediate phosphoranyl radical identical to that produced in the homolytic reaction of disulfides with phosphites. For thiophenol and triethyl phosphite, an ionic reaction to produce phenyl ethyl sulfide and diethyl phosphite is favored even in the presence of di- cr butyl peroxide (298). 

In this case, the initiator azobisisobutyronitrile, AIBN, was used to polymerize the MMA at 60°C, and then the sample was heated to 95 °C for the polymerization of the DACBA with t-butyl peroxy isononanate (TBPIN). 

Pryor [43,44] showed that the spontaneous polymerization kinetics of styrene were bimolecular and again postulated the D intermediate. Further evidences favoring this mechanism include 1) the identification of cis and trans 1,2-diphenylcyclobutanes as the major dimers [45], and 2) the large differences between spontaneous and chemically initiated (azobisisobutyronitrile) styrene polymerizations in the presence of the FR scavenger l,T-diphenyl-2-picrylhydrazyl (DPPH). The rate of consumption of DPPH is 25 times faster than that expected from rate of polymerization measurements. This difference was explained by the spontaneous formation of "D, many of which become self-terminated before initiating polymer radicals [46]. 

Ordered porous carbons were synthesized by replication of colloidal templates made from 30 - 100 nm diameter silica spheres and removal of the silica templates using aqueous HP. To create the templates, the monodisperse particles were pressed into pellets and then sintered slightly at their points of contact. The silica template were filled with carbon precursor solution of divinylbenzene (DVB) and a free radical initiator, azobisisobutyronitrile (AIBN). Polymerization and carbonization of the precursor solution and subsequent dissolution of the silica templates leave a polycrystalline network of carbon with interconnected uniform pores. The degree of order of the silica template is faithfully reproduced in the carbon replicas. 

Deoxy sugars. Radical reduction of the diol thiocarbonate (1) with this tin hydride with an initiator (azobisisobutyronitrile) in refluxing toluene gives, after alicaline hydrolysis, the 5-deoxy sugar (2). The isomeric 6-deoxy sugar (4) can... 

Figure 20-1. Dependence of the polymerization rate and number average degree of polymerization on the concentration of initiator, azobisisobutyronitrile, for the bulk polymerization of styrene at 60 C to yields of l%-3%. (After data from Pryor and Coco.) The dependence of the rate of polymerization on the initiator follows the square root law exactly.

Three typical free radical initiation reactions are snmmatized in Fig. 3.24. In the free radical initiation the center part of the initiator, azobisisobutyronitrile, can eject a stable nitrogen molecule. This gives the driving force to produce the two active free radicals. Before recombination, the free radicals can accomplish the thousands of propagation steps necessary to produce a macromolecule. 

Whether a monomer can be polymerized free-radically also depends in certain cases on the initiator. Azobisisobutyronitrile, for example, polymerizes 5-vinyl mercaptals CH2=CH—S—CH2—S—R to products of high molecular weight, whereas no polymer is formed at all under the same conditions with benzoyl peroxide. Here, in fact, the result is an induced decomposition of the benzoylperoxide by the ——CH2—S— group to form an (unstable) ester CH2=CH—S—CH(OCOC6H5)—S—R and benzoic acid. 

There are several interesting polymerization schemes intermediate between a sequential IPN and an SIN. For example, in in situ prepared sequential IPNs, both monomers are polymerized via free radical reaction (He et al. 1993 Rouf et al. 1994). The two monomers must have quite different reactivities toward the free radicals. This situation arises with vinyl or acrylic double bonds and allylic double bonds. The allylic double bonds react about 100 times slower than acrylic or methacrylic bonds. Often, two initiators are used, one reacting at a lower temperature and the other at a higher temperature. In one of the systems studied, based on methyl methacrylate and diallyl carbonate of bisphenol-A (DACBA), first, cross-linked PMMA was formed at moderate temperatures. Then, by just increasing the temperature after completion of the first polymerization, the synthesis of the allylic network followed. In this case, the initiator azobisisobutyronitrile, AIBN, was used to polymerize the MMA at 60 °C, and then the sample was heated to 95 °C for the polymerization of the DACBA with t-butyl peroxy isononanoate (TBPIN). 

The antagonistic effect of a mixture of two initiators, azobisisobutyronitrile and benzoyl peroxide, in the oxidation of cumene was attributed, using mathematical... 

HQ inhibition of the oxidation of acrylic acid and methyl methacrylate by 2 in the presence of initiator azobisisobutyronitrile has been compared with that for oxidation of acrylic acid by 4-methoxyphenol under the similar conditions. Reaction between the semiquinone radical and oxygen decreases the stoichiometric inhibition factor and the efficiency of HQ as the inhibiting agent. ... 

A free radical initiator azobisisobutyronitrile or an inhibitor, hydroquinone, have no effect on the rate of oxygen consumption. In any case a dissociative mechanism is precluded since autoxidation of uncoordinated phosphines is a radical process which gives mixed R P(OXOR)3 products. The mechanism suggested involves the formation and rearrangement of a cobalt dioxygen complex, equations (81) and (82), possibly via a dissociative oxygen insertion step of the type proposed by Halpem for platinum complexes. 

Chemically initiated processes. This section covers all proeesses in whieh free radicals are generated chemically or thermally from typieal free-radieal initiators (azobisisobutyronitrile, organic peroxides) as well as Ziegler-Natta eatalysts, organometallic systems, and donor aeeeptor eomplexes. 

Carbamazepine functional monomer, MAA, thick walled glass tube containing CBZ dissolved in porogen were used. The crosslinker, Trimethylolpropane trimethacrylate, and initiator, azobisisobutyronitrile, were also used. 20% of loaded CBZ was released from the imprinted nanospheres within the initial 6 h, while another 80% of CBZ was released in the following 9 days. [232]... 

Figure 22 Pressure dependence of the rate of polymerization at 70 X for CDB-mediated styrene bulk polymerization at three CDB levels initiator azobisisobutyronitrile concentration 1 x lO" mol The dashed line represents conventional polymerization, that is, without CDB, under otherwise identical conditions. From Arita, T. Buback, M. Janssen, 0. Vana, P. Macromol. Rapid Commun. 2004, 25,1376. ° ...

The reaaions of the radicals (whether primary, secondary, solvent-derived, etc.) with monomer may not be entirely regio-or chemoselective. Reactions, such as head addition, abstraction, or aromatic substitution, often compete with tail addition. In the sections that follow, the complexities of the initiation process will be illustrated by examining the initiation of polymerization of two commercially important monomers, S and methyl methacrylate (MMA), with each of three commonly used initiators, azobisisobutyronitrile (AIBN), dibenzoyl peroxide (BPO), and di-t-butyl peroxyoxalate (DBPOX). The primary radicals formed from these three initiators are cyanoisopropyl, benzoyloxy, and t-butoxy radicals, respectively (Scheme 7). BPO and DBPOX may also afford phenyl and methyl radicals, respectively, as secondary radicals. 

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