Polymerization of cyclic sulfides

Table 3. Cyclic oligomer formation during the cationic polymerization of cyclic sulfides in CH2C12 as solvent...

Again, these reactions, depending on the structure of monomer, may be reversible or irreversible. If resulting branched or macrocyclic onium ions are not reactive, i.e., they can not re-form the original active species either by intramolecular cyclization or by reaction with the next monomer molecule, then these reactions lead to termination (such a situation exists in the polymerization of cyclic sulfides or amines cf., Section 1II.D.E.). 

The factors, governing the reactivities of branched onium ions are of complex nature and will not be discussed here. It has been shown, however, that in the polymerization of cyclic sulfides and cyclic amines the formation of branched onium ions of the type ... 

The polymerization of cyclic sulfides and amines provided, although tentatively, some information on kp and kp. The equality k kp was found (the Kq value measured for an initiator used was further applied in the determimtion of a in polymerization studies) in the polymerization of 3,3-dimethylthietane in CgHsNOa and qualitatively for l-phenylmethyl-2-methyl-aziridine Small differences were found between kp and k (the macrocation being less... 

Table 12. Rate constants of propagation and activation parameters in the cationic polymerization of cyclic sulfides, amines and iminoethers at 0 °C... 

Other evidence stems from H-NMR studies of the polymerization of cyclic sulfides . 

The same phenomenon was observed in the polymerization of cyclic sulfides 4). Goethals has shown that in the polymerization of propylene sulfide linear polymer is formed first which then degrades to a mixture of cyclic oligomers, mostly to the cyclic tetramer 25). Thus, in several systems it was shown conclusively that cyclic... 

In some systems, mostly in the polymerization of cyclic sulfides and amines, the formation of polymeric onium ions is irreversible, i.e. the reactivity of these structures is so low that further propagation on these species does not proceed ... 

Polymerization of cyclic sulfides and amines can be initiated not only by the usual cationic and cationogenic compounds like Lewis and protonic acids, carbenium and oxonium salts and esters of strong acids, but also by alkyl halides, which are active enough to induce polymerization of some azetidines 9 10). 

In the polymerization of cyclic sulfides, cyclization becomes particularly important because of the enhanced basicity (and nucleophilicity) of the linear sulfides in comparison with their parent monomers43). The simplest cyclic oligomer, formed in the polymerization of thiiranes, is a dimer-1,4-dithiane or its derivatives. 1,4-Dithiane was first observed by Bell in the polymerization of ethylene sulfide 441 later Price isolated the styrene sulfide dimer 45) and recently Goethals obtained dimers of isobutylene and cyclohexene sulfides 46 . Structures of these dimers are ... 

As already mentioned and analysed in some detail in Vol. I (Adv. Polymer Sci. 37 (1980)), the cationic polymerization of cyclic sulfides and amines is accompanied by chain transfer to polymer. This type of transfer could become a termination, if the heteroatoms in the chain are more nucleophilic than those in the monomer ... 

When the polymerizations of cyclic sulfides are carried out with anionic initiators, many side reactions can occur. On the other hand, common anionic initiators, like KOH, yield optically active polymers from optically active propylene sulfide. An example of a side reaction is formation of propylene and sodium sulfide in sodium naphthalene initiated polymerizations. 

Describe the initiation and propagation reactions in cationic polymerizations of cyclic sulfides. 

What type of side reactions can occur in anionic polymerizations of cyclic sulfides ... 

Aliphatic polysulfides with two or more carbon atoms per monomeric unit are accessible through ring opening polymerization of cyclic sulfides or by the addition of thiol groups onto vinyl groups. In these cases, the anionic polymerization of cyclic sulHdes differs substantially from that of cyclic ethers. The ethyl anion attacks the carbon atom in cyclic ethers. But in the ethyl lithium initiated polymerization of propylene sulfide, a lithium ethane thiolate is first formed, and its anion then starts the polymerization of propylene sulfide ... 

The polymers obtained by polymerization of cyclic sulfides have no commercial importance. A monomer can be obtained from pentaerythritol, C(CH20H)4, and chloroacetaldehyde, CICH2CHO, which leads to sulfur-containing polymers when polycondensed with disodium sulfide ... 

The simplest chain structure -f-CH2—S- occurs through the polymerization of thioformaldehyde, CH2S, or its cyclic trimer (trithiane). Aliphatic polysulfides with two or more carbon atoms per monomeric unit are available through the polymerization of cyclic sulfides. The start step with organolithium compounds deviates from that of the epoxides in that initially the sulfur atom is attacked and subsequently the carbon atom is attacked. For example, the starting step with propylene sulfide and ethyl lithium initially gives propylene and lithium ethane thiolate ... 

The occurrence of an intermolecular termination reaction in the polymerization of thietane has been used to prepare star-shaped segmented copolymers. Oxonium ions are excellent initiators for the polymerization of cyclic sulfides and therefore addition of thietane to a living polyTHF solution results in the formation of a block copolymer. Since the thietane polymerization gives the termination reaction described above, the end result of this sequential monomer addition is a... 

Lastly, mention will be made of some methods for the formation of block copolymers containing poly(thioalkylene) sequences by the ring opening polymerizations of cyclic sulfides. 

Catalytic Properties. Mc30+BF4 has been used as a catalyst for the polymerization of cyclic sulfides and in the polymerization of THF to macrocyclic ethers. A valuable modem application is the catalytic Beckmann rearrangement of oximes in homogeneous liquid phase,the active species being a formamidinium salt. 

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