Acrylonitrile termination mechanism

It is very clear that if the initiator has hydroxyl groups, and if the termination takes place exclusively by recombination then a polymeric diol is obtained [2, 3], which is ideal for polyurethane. If the termination takes place by disproportionation, only monofunctional compounds are obtained, which cannot be used in PU. The vinylic and dienic monomers used in practice have various termination mechanisms. Some monomers give only recombination reactions, such as styrene, acrylates (methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethyl hexyl acrylate), acrylonitrile and butadiene. Other monomers give both mechanisms of termination, around 65-75% disproportionation and 25-35% recombination, such as methacrylates (methyl methacrylate, ethyl methacrylate, butyl methacrylate etc.), substituted styrenes and other monomers [2, 3, 4]. 

The efficiency of the cyclohexanone/Mn redox system for the polymerization of acrylonitrile and methyl methacrylate in perchloric acid and sulfuric acid media was investigated [81]. It was found that the rate of polymerization was independent of the oxidant concentration and varied linearly with the monomer and reducing agent concentration. Complex formation and termination mechanism was found to be different in two acidic media. In perchloric media, the termination is effected by the oxidant, whereas in sulfuric acid, primary radicals terminate growing chains. 

Studies of the particle—epoxy interface and particle composition have been helphil in understanding the mbber-particle formation in epoxy resins (306). Based on extensive dynamic mechanical studies of epoxy resin cure, a mechanism was proposed for the development of a heterophase morphology in mbber-modifted epoxy resins (307). Other functionalized mbbers, such as amine-terminated butadiene—acrylonitrile copolymers (308) and -butyl acrylate—acryhc acid copolymers (309), have been used for toughening epoxy resins. 

A similar phenomenon was postulated by Thomas and Pellon (10) to account for data obtained in the kinetics of acrylonitrile polymerization. They felt that it was possible to obtain unimolecular chain termination by a process of burial. This was conceived as a mechanism by which the growing chain became shielded from further growth by coiling or by embedding itself in the solid phase. At room temperatures we feel the... 

Similar mechanisms involving exciplexes and zwitterions were proposed for the formation of ortho adducts from anisole and 1,3-dioxoles [134,183] and from anisole with acrylonitrile [183], For the latter reaction, Mattay has proposed a zwitterion in which the terminal carbon atom of the double bond of acrylonitrile... 

Problem 30.8 Draw a stepwise mechanism for the conversion of acrylonitrile (CH2=CHC=N) to polyacrylonitrile, - [CH2CHC =N] -, using butyllithium (BuLi) as the initiator and C02 as the electrophile to terminate the chain. 

Dainton and Tordoff (9) showed that in the case of acrylamide Fe+ OH is a significant terminator. I am not, however, convinced of the validity of their suggested extension of this mechanism to other vinyl monomers, and similar generalizations, particularly in view of the fact that under otherwise identical conditions in experiments concerning the oxidation of benzoic acid (4) a doubled maximum yield of ferrous ion formation was determined by straightforward analytical methods, indicating that in the latter case, but not in the former, Fe+ OH must be considered as a terminator. This is quite independent of the quantitative estimate of the Fe+30H primary yield, which has become controversial. It is, however, feasible that Fe+ Br did not act as photoinitiator of the polymerization of methyl methacrylate or acrylonitrile because of eflficient termination with Fe+ Bir, which would not be unexpected. 

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