Azobisisobutyronitrile , photoinitiation

Our application of the rotating sector technique to hydrocarbon oxidations has been described (14,15,18). Oxidation rates were measured at the longest convenient chain lengths and corrected for the absorption and evolution of gas in initiation and in peroxy radical-peroxy radical reactions. ,a -Azobiscyclohexylnitrile (ACHN) was used as the photoinitiator at 30°C. and a,a -azobis-l-propanol diacetate as the photoinitiator at 56°C. ,a -Azobisisobutyronitrile (AIBN) was used as a thermal initiator at 30° and 56°C. 

The 2-ethylhexyl acrylate, vinyl acetate, acrylic acid, 2-hydroxyethyl methacrylate, and 2,2 -azobisisobutyronitrile (AIBN, as initiator for polymerization) used for preparing UV-crossHnkable acrylic PSAs were obtained from Junsei Chemicals Co. and used as received. The photoinitiator P-36 containing a double bond was obtained from SK UCB Co., Korea. The typical synthetic method was as follows (see Table 17.1). 2-EHA (120 g), VAc (22.5 g), AA (7.5 g), AIBN (0.3 g), and ethyl acetate (75 g) were aU mixed in a 500 mL four-necked flask equipped with a stirrer, dropping fuimel, and thermometer. The polymerization reaction was initiated at 70 °C. After this temperature had been maintained for 1 h, ethyl acetate (75 g) containing P-36 (1.5 g) was gradually added to the flask while it was stirred for 1 h, and then the polymerization was carried out at 70-75 °C for another 5 h. All of the syntheses were carried out in a flask wrapped in aluminum foil... 

Polymerization-inducing free radicals can also be photochemically produced. For example, the azo group of azobisisobutyronitrile absorbs 350 nm light, whereby the molecule decomposes with the formation of iso-butyronitrile free radicals [see Equation (20-11)]. Certain aliphatic ketones also form free radicals under the action of light (see also Chapter 21). These photoinitiated polymerizations do not require any thermal activation energy... 

I photoinitiators such as azobisisobutyronitrile (AIBN) and benzoin methyl ether (BME), typically used to generate free radicals during monolith formation, can play the very same role as type... 

The acetylacetonate complexes of cobalt(II) and manganese(111) are efficient catalysts for the thermally intiated oxidation of tetralin, but do not influence the photoinitiated process. The reverse situation is observed for the iron(III) and cobalt(III) complexes [70a]. The thermal oxidation can be influenced by the addition of free-radical initiators like t-butyl hydroperoxide or 2,2 -azobisisobutyronitrile [70b]. 

Some initiators can function as both, thermal and photoinitiators. Such an initiator, for instance, is 2,2 -azobisisobutyronitrile. Also, Engel and coworkers [16] reported synthesis of an initiator that can function both as a thermal free radical initiator and a photoinitiator (see Sect. 3.2.4). It can be illustrated as follows ... 

Table 3 contains a listing of commercial photoinitiator chemicals. For the EB systems, accelerators may belong to a fairly wide range of chemicals, but they are all quite polar in nature. For IR systems peroxides or azobisisobutyronitrile are utilized. Some of the UV curables contain a combination of UV and IR initiators to take advantage of the IR output that many UV lamps generate. Table 4 shows an example of a UV curable formulation. 

If the monomer itself cannot form free radicals by this process, then a photoinitiator must be added. Bisulfides form two free radicals RS on irradiation. The azo group of azobisisobutyronitrile absorbs light at 350 nm and then forms free radicals [reaction (20-3)]. Certain aliphatic ketones decompose according to a Norrish type I mechanism into two free radicals ... 

Another widely used structural variation of class I photoinitiators are azoinitiators, which are also employed as thermal initiators. However, their mechanism of photodecomposition is markedly different from acetophenone-type initiators. Equation 11 shows the UV-induced decomposition of the widely used azoinitiator 2,2 -azobisisobutyronitrile (AIBN). 

Azoinitiators may also be used as photoinitiators. They decompose upon irradiation by a mechanism that is markedly different from the acetophenone type. By example of 2,2-azobisisobutyronitrile (AIBN), this mechanism is shown in Scheme 1.6. 

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