Anionic chain polymerization nitriles

The anionic chain polymerizations of polar monomers, such as methyl methacrylate, methyl vinyl ketone and acrylonitrile, often yield complex polymer structures due to nucleophilic reactions of the carbonyl and nitrile groups. 

Anionic polymerization is a powerful method for the synthesis of polymers with a well defined structure [222]. By careful exclusion of oxygen, water and other impurities, Szwarc and coworkers were able to demonstrate the living nature of anionic polymerization [223,224]. This discovery has found a wide range of applications in the synthesis of model macromolecules over the last 40 years [225-227]. Anionic polymerization is known to be limited to monomers with electron-withdrawing substituents, such as nitrile, carboxyl, phenyl, vinyl etc. These substituents facilitate the attack of anionic species by decreasing the electron density at the double bond and stabilizing the propagating anionic chains by resonance. 

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... 

Fig. 3.50. Number of chain scissions as a function of time of photo-oxidation of different polystyrenes (a) redox initiated (b) AIBN (azo-bis-isobutyro nitrile) (c) thermal (80 °C) (d) thermal (60 °C) and (e) anionic polymerized [2242]. (Reproduced with permission from [2242] published by Elsevier Science Publishers Ltd, 1989.)...

Anionic polymerization requires a type of monomer that contains an electron-withdrawing substituent such as phenyl, carboxyl, nitrile, and diene. Successful industrial examples are some styrenic products such as styrene-butadiene mbber (SBR) and styrene-butadiene-styrene (SBS) thermoplastic elastomer resins. Commonly used industrial catalysts are ethyl lithium (C2H5li) and sodium naphthalide (CioHgNa), which quickly dissolves and dissociates in a proper solvent. The primary anion R" reacts with monomer and initiates chain growth through successive propagation steps ... 

---