Oxirane Ethylene Oxide, EO

Linear polyEO of relatively high molecular weight (Mn up to 2 104) was obtained by cationic polymerization only with SnCl4 as initiator 6). The following mechanism, based on the well-known ability of tetravalent tin compounds to form hexacoordinate complexes, was proposed  

the growing species was regarded to be a bifunctional internal oxonium ion 1). A bifunctional character of the SnCl4 initiator has been recently confirmed for l-tert-butylperoxy-2,3-epoxypropane7)  

Balaev determined the concentration of active species for this monomer (measured by Saegusa s end-capping method8 as a 2[SnCl4]0 and being largely independent of monomer conversion. Polymerization was conducted in benzene solvent ([M] = 1 mol r ) at 22 °C with [SnCLJo = 5 10 2 mol T1. 

In SnCl4-initiated polymerizations the product distribution is intermediate between a typical cationic (e.g. BF3-initiated) and coordinative polymerization. 

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