Sulfonium zwitterions, polymerization

Evidence to support hypothesis (ii) comes from Schmidt s observation that when salt is added, fewer macrocycles are formed during cyclic sulfonium zwitterion polymerizations. 

However, cyclic sulfonium zwitterions without two molecules of water are unstable and polymerize due to the nucleophilic attack of the anion (0 ) on the tetra-hydrothiophenium ring followed by ring opening with consecutive polymerization. Products of polymerization are low molecular weight linear polymers and cyclic dimers and trimers (6,7) ... 

The polymerization of two aryl sulfonium zwitterions has been studied in detail. 

Charge cancellation polymerizations must be considered as special cases. Some degree of charge separation already exists in acetonitrile oxide but a base is required to initiate its polymerization. Although linked by a conjugated system ionisation is essentially complete in cyclic sulfonium zwitterion monomers. No initiator is required and monomeric units add at both ends of the p>olymer chain. The initial step in the general scheme above is best considered as part of monomer synthesis. 

In the copolymerization with PPL, only route a has been considered by Saegusa, and transfer was not taken into account. Macrocyclization by end-to-end closure is another possibility, however, these macrocycles cannot easily be isolated and studied. The presence of macrocycles may be corroborated by comparison of DPn determined from end-groups with those measured by other methods e.g. GPC, osmometry, etc., i.e. when cyclic and linear molecules are counted separately. Such macrocycles were indeed observed by Schmidt in the polymerization of aryl sulfonium zwitterion 86) ... 

SCHMIDT Polymerization of Aryl Cyclic Sulfonium Zwitterions 323... 

The polymerization of LXIII, a stable isolable zwitterion, on heating or photolysis involves nucleophilic attack by phenoxide anion on the cyclic sulfonium ring [Hoyle et al., 2001 Odian et al., 1990]. The reaction proceeds as a step polymerization. 

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