Low-molecular weight azo compounds

Low-molecular weight azo compounds have frequently been used in cationic polymerizations producing azo-containing polymers. Thus, the combination of ionically and radically polymerizable monomers into block copolymers has been achieved. Azo compounds were used in all steps of cationic polymerization without any loss of azo function as initiators, as monomers and, finally, as terminating agents. 

Regarding anion radical transfer, low-molecular weight azo compounds were used as terminating agents in anionic polymerizations. An interesting example is the addition of a living polystyrene chain to one nitrile group of AIBN [71]. The terminal styryl anion is likely to form... 

III. BLOCK COPOLYMER SYNTHESIS WITH LOW-MOLECULAR WEIGHT AZO COMPOUNDS... 

Scheme 12.7 Preparation of azo BCs by supramolecular self-assembly between a BC and a low molecular weight azo compound. Source Reproduced from Sidorenko et al., 2003.

Rau J, Maris B, Kinget R et al (2002) Enhanced anaerobic degradation of polymeric azo compounds by Escherichia coli in the presence of low-molecular-weight redox mediators. J Pharm Pharmacol 54 1471-1479... 

Polymers containing azo groups are employed either in a solvent or they can simply be dissolved in the graft monomer. In all cases which have been reported, the polymeric azo compounds have kinetic characteristics analogous to their low-molecular-weight analogues, i.e. they conform with the general formula ... 

A New Molecular Crystal DEANST. Another example of a low molecular weight compound with a large third-order NLO property is a styrene derivative. By selecting an appropriate -conjugation length and chemical structures of donor and acceptor, several new organic molecular crystals such as stilbene and azo benzene derivatives which exhibit %(3) larger than 10 12 esu can be developed. The %(3) of 4-(N,N-diethylamino)-4 -nitrostilbene (DEANS), an intramolecular CT compound, has been reported in a solution, in a polymer matrix and in a crystalline state(27.29.30). 

You met diazonium salts in Chapter 22. Arene diazonium salts are stable compounds, but alkyl diazonium salts, which are formed by protonation of diazo compounds, are not. They decompose rapidly with loss of N2—this was how the carboxylic acid got methylated at the beginning of the chapter. Other relatives of the azo and diazo compounds are alkyl azides. Alkyl azides have three nitrogen atoms and are usually stable but azides of low molecular weight may explode on impact or heating. 

Disperse Dyes Nonionic dyes insoluble in water and used mainly as fine aqueous dispersions in dying acetate, polyester, and polyamide fibers. A large subclass of disperse dyes comprises low-molecular-weight aromatic azo compounds with amino, hydroxy, and alkoxy groups that fix on fibers by forming van der Waals and hydrogen bonds. 

Instead of a reducing agent for decomposing peroxides or azo compounds, UV irradiation can be applied for splitting initiator. Millan et al. [319,321,366] describe the use of an ultraviolet beam to activate initiator decomposition at low temperatures. In a series of experimental procedures it was established that at 0°C a molecular weight of Mn = 320000 can be obtained. Results similar to those discussed for borane-initiated polymerization in reference to tacticity, thermal stability, and branching were obtained. This technique has very little practical value because special equipment is required. 

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