Anionic polymerization of thiiranes

The anionic polymerization of thiiranes appears to proceed very clearly and in a well defined manner. Living systems have been found and good kinetic measurements have been possible [36]. The base catalysed polymerization of ethylene sulphide (ES) was probably one of the earliest thiirane polymerizations noted. However, the studies have been hindered because the polymer formed is highly crystalline and insoluble. Homogeneous solution studies have not been possible. Propene sulphide (PS) on the other hand gives soluble amorphous polymer and has been amenable to careful study. Indeed the formation of amorphous polypropene sulphide is the major evidence that base catalysed polymerization is ionic and proceeds by the reactions indicated by the equations... 

Anionic polymerization of thiiranes, e.g. 2-methyl-2-ethyl thiirane27, initiated by carbazyl or fluorenyl salts in tetrahydrofuran, also yields living polymers, see p. 152. 

The anionic polymerization of thiiranes had been studied in detail during the 1960s and 1970s by Boileau, Sigwalt, and their co-workers. Thiirane and various substituted thiiranes, especially MT, have been polymerized to high-molecular-weight polymers by various anionic initiators. Hie active species of the polymerization are of the thiolate typ>e (Scheme 23). 

The anionic polymerization of thiiranes is also initiated by tertiary amines, of which l,4-diazabicyclo[2.2.2]octane... 

Alkoxide-Type Initiators. Using the guide that an appropriate initiator should have approximately the same structure and reactivity as the propagating anionic species (see Table 1), alkoxide, thioalkoxide, carboxylate, and silanolate salts would be expected to be useful initiators for the anionic polymerization of epoxides, thiiranes, lactones, and siloxanes, respectively (106—108). Thus low molecular weight poly(ethylene oxide) can be prepared... 

Anionic copolymerization of thiiranes with elemental sulfur 91PS(59)47. Polymerization of thiiranes 93PS(74)71. 

The anionic polymerizations of racemic mixtures of thiiranes described above generally lead to atactic polymers. When one pure enantiomer is polymerized, the asymmetric center remains unchanged and the resulting polymer is isotactic. This polymer is optically active and has quite different physical properties compared with the atactic analog. Isotactic polyMT, for example, is a crystalline material with a melting point of up to 63 ° whereas the atactic polymer is an amorphous material. 

Values of Ku for alkoxide, thiolate and carboxylate species with Li, Na or K counterions, determined in the anionic polymerization of EO and CL, ethylene sulfide (thiirane) and PL polymerization, lie in a very broad range of values, from... 

The most important reaction with Lewis acids such as boron trifluoride etherate is polymerization (Scheme 30) (72MI50601). Other Lewis acids have been used SnCL, Bu 2A1C1, Bu sAl, Et2Zn, SO3, PFs, TiCU, AICI3, Pd(II) and Pt(II) salts. Trialkylaluminum, dialkylzinc and other alkyl metal initiators may partially hydrolyze to catalyze the polymerization by an anionic mechanism rather than the cationic one illustrated in Scheme 30. Cyclic dimers and trimers are often products of cationic polymerization reactions, and desulfurization of the monomer may occur. Polymerization of optically active thiiranes yields optically active polymers (75MI50600). 

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