2,2 -Azobis-isobutyrate

The chlorination of methylchlorosilanes is realised by free chlorine in the liquid or gaseous phase. The reaction takes place by the radical chain mechanism its initiators (substances capable of generating free radicals) can be peroxides (benzoyl, kumyl, etc.), the dinitrile of 2,2 -azobis(isobutyric) acid, fluorine, 60Co y-rays, as well as UV rays. 

It is more practical to chlorinate organochlorosilanes with the help of initiators. The use of radical initiators (the dinitrile of 2,2 -azobis(isobutyric) acid, etc.) allows to carry out the chlorination reaction in the dark. This chlorination method is known in the literature as the dark technique. 

Raw stock dimethyldichlorosilane (not less than 99% of the main fraction) liquid chlorine (not less than 99.5% of chlorine, not more than 0.06% of humidity) initiator is the dinitrile of 2,2 -azobis(isobutyric) acid (the melting point is 105-106°C, not more than 0.5% of humidity), used as a 2% solution in dimethyldichlorosilane. 

A method for preparing isolatable and re-activatable polymethyl methacrylate using the chain transfer agent bis(ethoxythiocarbonyl)disulfane with 2,2 -azobis(isobutyr-onitrile) is described. Reactivation of this macroinitiator with 2,2 -azobisisobutyr-onitrile was then used to prepare block copolymers. 

Objections have been raised to the use of AIBN because wasted radicals can give rise to a toxic product, namely tetramethylsuccinodinitrile. For this reason, increasing attention is being paid to the azoester dimethyl 2,2 -azobis-isobutyrate (AZE), Me2 C(COOMe) N N C (COOMe) Me2 which dissociates at 60°C at about the same rate as AIBN. The first reports on applications of [ C]AZE have been published [4,5]. 

The propagating radical of dialkyl itaconate in the homogeneous polymerization was foimd by Sato et al. to be stable enough to be observed by ESR even above 60 °C. Fig. 62 a displays the 5-line spectra obtained when dimethyl 2,2 -azobis-isobutyrate, benzoylperoxide, and di-tert-butylperoxide were used as initiators. On the other hand, the polymerization of DBI initiated with azonitriles such as 2,2 -azobisisobutyronitrile, 2,2 -azobis(2,4-dimethylvaleronitrile), and cyclohexanecarbo-... 

Isotopic enhancement may be also illustrated by Bevington et al. s exploration of the use of the C-enriched free radical initiators 1,1 -azobis(phenylethane) and AIBN in preparing butadiene polymers [51] and the use of dimethyl 2,2 -azobis(isobutyrate) to initiate the polymerisations of styrene, acrylonitrile, methyl methacrylate and methyl acrylate [52]. The signals from the ends are thus rendered more intense, and b ome observable in a standard NMR spectrum, where they display information on the manner in which the initiator radicals have attacked the first monomer to become incorporated at the start of the polymer chain one can thus compare initial and mean tacticities. In a further use of isotope enrichment, Moad and Willing found that selective enrichment... 

Bates, E. S., Wignall, G D. Observation of a persistent methacrylate radical in the decomposition of methyl 2,2 -azobis(isobutyrate) and the polymerization of methyl methacrylate. Macromolecules, 19, 934-936 (1986). 

Sato, T., Arima, Y, Seno, M., Hirano, T Initiator-fragment incorporation radical polymerization of divinyl adipate with dimethyl 2,2 -azobis(isobutyrate) kinetics and formation of soluble hyperbranched polymer. Macromolecules 38(5), 1627-1632 (2005)... 

Other techniques. An example of the value of ESR for conducting kinetic studies over a wide conversion range has recently been published by Yamada et al. [37]. Values of kp and kt for styrene polymerization (Figs. 3 and 4) were determined from 0 to 100% conversion initiated using dimethyl 2 -azobis(isobutyrate) at 70 C. These figures show the concentration of polystyryl radicals versus conversion and time, and the change in kp and k, with styrene conversion. 

AIBMe azobisfmethyl isobutyrate), 2,2 -azobis(methyl 2-niethylpropionate)... 

Oligobutadiene with two ester-end groups. Eight g. of azobis(methyl isobutyrate) was introduced into a glass pressure vessel ("Laborautokav" Buchi Comp., CH-Uster, Switzerland). Butadiene, 177 g., was condensed into the evacxiated vessel. The reaction mixture was heated to 80°C for 24 hrs. Excess of butadiene was distilled off, the final traces at 90OC. in vacuum. 

Figure lb. GPC of azobis(methyl isobutyrate) prepared with large amounts of an initiator. Abscissa shows chart distance in centimeters, ordinate shows differential... 

Some initiators (e.g., dibenzoyl peroxide and potassium per-oxydisulfate) and the derived radicals may oxidize RAFT agents to sulfme or other products. Other initiator radicals may react with the RAFT agent to form a stable thiocarbonylthio compound. It is important that the initiator-derived radical is a good leaving group with respect to the propagating radical. For example, use of an aliphatic diacyl peroxide (e.g., dilauroyl peroxide) will provide a relatively stable RAFT agent with R = primary alkyl. Similarly, azobis(methyl isobutyrate) (AIBMe) is not a suitable choice for RAFT polymerization of MMA. ... 

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