Spontaneous alternating zwitterion copolymerizations

This type of copolymerization results from spontaneous interactions of nucleophilic and electrophilic monomers (M and Mg, respectively) without any additions of catalysts. Zwitterions form in the process that subsequently leads to formation of polymers [214-226]. The mechanism is a step-growth polymerization. It can be illustrated as follows  

Repeated additions of the charged species and the resulting zwitterionic products lead to high polymers  

The initial zwitterion that forms upon combination of a nucleophilic with an electrophilic monomer is called a genetic zwitterion [214]. Intramolecular reactions can produce macrocycles  

The contribution of the cyclization reaction, however, is, apparently, small [214]. A reaction can also take place between a free monomer and any zwitterion at one of the ionic sites  

Such reactions disturb the alternating arrangements of the units in the products. The 

Such reactions disturb the alternating arrangements of the units— Mn-Me—in the products. The reactivity of the monomers determines whether homopropagations occur as well. Alternating propagation depends upon dipole-dipole interactions between Mn and Me monomers in 

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Table 15.6. Examples of zwitterionic, spontaneous, alternating copolymerization... 

A novel type of spontaneous alternating copolymerization, developed by Sae-gusa, leads to copolymer formation via a zwitterion, in whieh both the propagating ion and the gegen ion are situated at opposite ends of the ehain. In general, an electrophilic monomer (Mg) internets with a nueleophilie monomer (M ) in the absenee of eatalyst to form a dimerie dipolar speeies. 

The addition of a Lewis acid to a polymerization recipe involving free radical initiators makes possible copolymerizations which would not otherwise occur e.g. Isobutene + methyl acrylate. The copolymerizations may also be unaffected by the addition of inhibitors or transfer reagents. Spontaneous alternating copolymerization may also occur between nucleophilic (Mn) and electrophilic (Mb) monomers through zwitterion intermediates (5) which are capable of propagation (6). 

Random copolymerization of different oxazolines is described in Section 15.1,2.2. The reactivity ratios increase as expected with monomer basicity 18). Statistical copolymers of cyclic imino ethers with other groups of monomers are not known, although oxazolines and oxazines form readily alternating copolymers with a number of electrophilic monomers by spontaneous zwitterionic polymerization. The mechanism and examples of this process are discussed in Section 15.2.1. 

Later Kagiya et al. described the zwitterionic spontaneous copolymerization of P-propiolactone with different aziridines69), and since 1972 Saegusa has started extensive studies of zwitterionic alternating copolymerization 70 79). In most of these systems the molecular weights of the copolymers are low. 

T. Saegusa, Spontaneously occurring alternating copolymerization via zwitterion intermediaries, Angew. Chem. Int. Ed. Engl. 16, 826(1977). 

EtO CN P p CN H COOMe COOMe Spontaneous copolymerization with 2-oxazolines, CH3NO2, RT Alternating copolymerization by a step-growth mechanism (combination of zwitterions) [69]... 

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