2,2 -Azobis-isobutyronitrile -initiated

The methacrylate group of lEM allows it to be free radical polymerized Thomas (1) reports lEM can be solution polymerized in dry solvents using AIBN (azobis-isobutyronitrile) initiator to give a stable polyisocyanate. The homopolymer of lEM retains 90-95% of its isocyanate functionality and has a glass transition... 

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... 

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. 

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

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... 

Initiators commonly used include dibenzoyl peroxide, lauryl peroxide, 2, 2 -azobis isobutyronitrile, and others that are suitable for use in the temperature range of approximately 60-90°C. 

For perhaps a century, the primary interest in azo compounds has been in dye chemistry. Recently, aliphatic azo compounds, which are thermally less stable than their aromatic counterpart, have enjoyed attention as sources of free radicals for polymerization reactions. In this regard, an initiator such as a,a -azobis(isobutyronitrile) is important for two reasons ... 

Gels are prepared by free-radical bulk copolymerization. The comonomers (n-AMA and DMA at a specified molar ratio) are injected along with the crosslinker (DVB 0.1% w/w) and the initiator [2,2 -azobis(isobutyronitrile) (0.5% w/w)] between two glass plates. The glass is previously silanized by immersion for two days in a solution of dichlorodimethylsilane (2% v/v) in toluene. The plates are separated by Teflon spacers of specified thickness, and the whole assembly is held together by metal damps. Polymerization is accomplished by incubating the assembly in the vertical position under argon at 60 °C for 18 h. 

Measurements on a-Methylstyrene—Acrylonitrile. Polymerizations were carried out in dilatometers without solvent. Initiator was azobis-isobutyronitrile. At 100 °C the reaction was initiated thermally. At 0° and 20 °C the reaction was carried out in flasks in a thermally controlled room. Yields were below 5%. The composition of the copolymers was calculated from nitrogen determination (Kjeldahl method). In an older reference (29) polymerizations were carried out at 20°, 50°, 60°, and... 

Physical entrapment or chemical coupling is a well-established procedure for MIP preparation. First, a complex is formed between a functional monomer and template in an appropriate solvent solution. Then the complex is immobilized by polymerization in excess of a cross-linker. Predominantly, free-radical polymerization thermally launched with a 2,2-azobis(isobutyronitrile) (AIBN) initiator, is performed. In the case of photo-radical polymerization, a benzophenone or acetopho-none derivative is also used as the initiator [101]. Next, the template is extracted by rinsing the resulting MIP block with a suitably selected solvent solution. The bulk... 

Quantitative information on the antioxidant actions of allicin (by radical scavenging through one-step allylic hydrogen transfer) against the oxidation of cumene and methyl linoleate (ML) initiated with 2,2/-azobis(isobutyronitrile) in chlorobenzene has been obtained.283... 

The two most important classes of radical initiators are azo-compounds and peroxides (Fig. 10.1). The most commonly used azo-initiators are 2,2/-azobis(isobutyronitrile) (AIBN) and l,l/-azobis(cyclohexane-l-carbonitrile) (ACN). The shorter half-life of AIBN ( ti/2 = 1.24 h at 80°C in benzene) has led to international shipping restrictions and ACN (ti/2 = 29.61 h under the same conditions [l])isbecominganincreasinglyvaluablereplace-ment. As explained in Section 10.4, however, this appreciable difference in decomposition rate means that ACN cannot replace AIBN as an initiator for all radical reactions. Furthermore, AIBN is soluble in a wider range of solvents, polar as well as non-polar (including alcohols, acetonitrile and benzene), compared with ACN which is restricted to use in nonpolar solvents, such as benzene, toluene and cyclohexane. 

Radical initiators are thermally labile compounds, which decompose into radicals upon moderate heating. These radicals initiate the actual radical chain through the formation of the initiating radical. The most frequently used radical initiators are azobis-isobutyronitrile (AIBN) and dibenzoyl peroxide (Figure 1.9). After AIBN has been heated for only 1 h at 80°C, it is half-decomposed, and after dibenzoyl peroxide has been heated for only 1 h at 95°C, it is half-decomposed as well. 

Bicyclic eight-membered ring phosphorus compounds are usually obtained by the free radical reactions of the corresponding alkenes with phosphines. In most cases, these reactions require the presence of such free radical initiators as azobis(isobutyronitrile) (AIBN) or azobis(isovaleronitrile) (VAZO). 

Other advantages of C02-based polymerizations are that there is no chain transfer to the solvent, and that the production of unstable end groups can be dramatically reduced. Guan et al [4] studied the decomposition of 2,2 -azobis-(isobutyronitrile) (AIBN) in SCCO2. It was found that initiator efficiencies greater than 80% were possible due to the low viscosity of CO2 and negligible solvent cage effects. Additionally, analysis of the decomposition products showed that there was no chain transfer to CO2. 

Living anionic polymerization of methacrylates and acrylates can be used to prepare macromonomers, which can thereafter be polymerized by any technique known in the state of the art. For instance, Flatada and coworkers reacted anionic ft)-hydroxyl-PMMA (55), which was then polymerized by radical polymerization into the corresponding combshaped copolymer (81) with 2,2 -azobis(isobutyronitrile) (AIBN) as initiator (equation 64). ... 

The MIP is usually prepared as a highly cross-linked, rigid bulk polymer and the polymerisation reaction is initiated by photo- or thermo-labile free radical initiators such as 2,2 -azobis(isobutyronitrile). For molecular imprint-based CEC systems, the introduction of the imprinted polymer into the capillary column has been focused on and several approaches have been developed (see below). The polymerisation process can be performed in between 1 and 24 h. It has been shown that the temperature during the polymerisation process is important. A lower temperature leads to imprinted polymers with higher selectivity [47] or better chromatographic performance [39]. 

Hydrosilylation of unsaturated hydrocarbons is the most essential procedure for creating Si-C bonds. It is an addition of Si-H units across ir-systems such as C=C double or C=C triple bonds and may occur on two different reaction modes. Radical hydrosilylation is initiated with ultraviolet (UV) hght, y-irradiation, or radical starters such as azobis(isobutyronitrile) (AIBN) or peroxides. However, there are some drawbacks which have to be taken into account, such as competition of... 

Hydrostannation with tricyclohexyltin hydride is only successful with unactivated unsaturated compounds when the reaction is conducted at high temperature (110 °C) with azobis(isobutyronitrile) added portion-wise, as an initiator. Under these conditions, it gives the expected adducts 29, 32, 34, 36, 38, 40, 43, 45, 48, and 50 in good yields with total regiospecificity, the tin being linked to the terminal carbon atom of the unsaturated compound (Scheme 3.7.3). Hydrostannation of unactivated alkenes with tricyclohexyltin hydride has been reported up to now as being unsuccessful, even under high pressure. ... 

A thermal initiator is typically either an azo compound or a peroxide based initiator, e.g., 2,2 -azobis-isobutyronitrile. Each initiator molecule can decompose to give one or two primary radicals (R ) and possibly inert by-products. Initiation rate constants for several common thermal initiators are listed in Table 1. Each primary radical can attack a monomer molecule (M) to initiate a polymer chain (P ). The recombination... 

Marvel and McCain 49> have shown that ethyl cinnamate can be homopolymerized by use of typical radical-type thermal initiators, such as benzoyl peroxide or 2,2 -azobis(isobutyronitrile). Ethyl cinnamate and poly(vinyl cinnamate) can, therefore, take part in radical addition reactions. 

Table 2. Activation parameters for the polymerization of vinyl trimethylacetate in various solvents initiated by (n-Bu)3B or 2,2 -azobis-(isobutyronitrile) (AIBN)89 ...

Most functional monomers and cross-linkers contain one or more vinyl functionalities. Polymerization of this type of compound for the preparation of MIPs is traditionally performed as a free-radical polymerization, initiated via either ther-molytic or photolytic homolysis of an initiator. One of the most commonly used free radical initiators for this purpose is 2,2 -azobis (isobutyronitrile) (AIBN). Other examples of free-radical polymerization initiators are phenyl-azo-triphenyl-methane, tert-butyl peroxide (TBP), acetyl peroxide, benzoyl peroxide (BPO), lauroyl peroxide, tert-butyl hydroperoxide and tert-butyl perbenzoate. 

Scheme 32 Main structures of carboxy-functional poly( -butyl acrylate) (PBA) synthesized by RAFT polymerization initiated with either a,a -azobis(isobutyronitrile) or 4,4 -azobis(4-cyanovaleric acid)...

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