Thiirane polymerization

The main components of cyclic fraction in thiirane polymerization are cyclic dimer and cyclic tetramer [158],... 

The additional feature of thiiranes polymerization is the possibility of formation of isomerized products containing sulfur-sulfur bond, with expulsion of an olefin as shown for dimethylthiirane polymerization. 

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... 

It should be noted that thiiranes polymerize under these basic conditions much more rapidly than the corresponding epoxides. Direct comparison of the rates is not possible because the same temperature range could not be used. 

It has long been known that acids will initiate a thiirane polymerization reaction. By analogy to the oxygen compounds it was reasonably suggested that propagation occurs via a cyclic sulphonium ion. The relatively greater ease of formation of a sulphonium ion compared to an... 

The coordinate type catalysts are also effective for thiirane polymerizations. The types of systems used are also similar. Thus diethylzinc and in particular diethylzinc/water mixtures have been studied [44]. Other studies made using triethylaluminium and diethylcadmium indicated that these metal alkyls all behave similarly. The reactions seem to be rather complex, and, as also was the case with the epoxides, no well defined kinetic studies have appeared. The polymers produced are of high molecular weight and are often crystalline. Thus stereospecific polysulphides have been reported. Again the bulk of the studies involve PS. Stereoselective polymerization of racemic monomer has been accomplished [45, 46] using a catalyst prepared from diethylzinc and (+) borneol. The marked difference between PO and PS in their polymer-... 

Higher conversions in thiirane polymerizations, however, proceed with a chain scission... 

Higher conversions in thiirane polymerizations, however, proceed with chain scission transfer mechanism under the influence of BF3 (C2H5)20 [192]. This is indicated by a change in the molecular weight distribution, a bimodal character. When the reaction is complete there is a marked decrease in the average molecular weight of the polymer. When thietane polymerizes with triethyl-oxonium tetrafluoroborate initiation in methylene chloride, the reaction terminates after only limited conversion [193]. This results from reactions between the reactive chain ends (cyclic sulfonium salts) and the sulfur atoms on the polymer backbone. In propylene sulfide polymerization, however, terminations are mainly due to formations of 12-membered ring sulfonium salts from intramolecular reactions [193]. 

Another method of obtaining sulfur-containing oligomers and polymers is thiirane polymerization. In the presence of proton donors (e.g., H2S and ditiols), thiiranes polymerize with the formation of polythyolesterditiols. 

The initiator system 2a/DBU was formed by addition of DBU ([2a]/[DBU] = 1 1), which leads to the thiolate/thiol equilibrium through proton exchange The polymerization of MT using this initiator system was carried out in DMF at 0 °C and was quenched by l-(chloromethyl)naphthalene, which has been reported to be effective for termination of thiirane polymerization. With a feed ratio of [MT]o/[2a/DBU]o = 30, the reartion was complete within 5 min to afford the corresponding star-shaped polymer the nrrmber-average molecular weight (M ) and MWD (Mw/MJ, which were 3500 and 1.05, respectively. 

The thiolate chain ends in thiirane polymerizations are unreactive toward hydroxyl groups and even toward water. 

Distribution of polymer fractions in r-butyl thiirane polymerization with different initiator systems... 

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). 

Phosgene reacts exothermically with thiirane in two steps (Scheme 36) (77MI50602). 3,5-Dinitrobenzoyl chloride and benzoyl fluoride initiate polymerization of thiirane. A novel reaction of benzoyl isocyanate or trichloroacetyl isocyanate, which yields ethylenethiol derivatives from epithiochlorohydrin (2-chloromethylthiirane), 2-methylthiirane or cyclohexene episulfide, has been reported (Scheme 37) (71BAU2432). 

Treatment of thiiranes with lithium aluminum hydride gives a thiolate ion formed by attack of hydride ion on the least hindered carbon atoms (76RCR25), The mechanism is 5n2, inversion occurring at the site of attack. Polymerization initiated by the thiolate ion is a side reaction and may even be the predominant reaction, e.g. with 2-phenoxymethylthiirane. Use of THF instead of ether as solvent is said to favor polymerization. Tetrahydroborates do not reduce the thiirane ring under mild conditions and can be used to reduce other functional groups in the presence of the episulfide. Sodium in ammonia reduces norbornene episulfide to the exo thiol. 

Thiirane, 2-phenyl-conformation rotational barriers, 7, 138 polymerization, 7, 144 Thiirane, tetraaryl-synthesis, 7, 175 Thiirane, tetrafluoro-halogenation, 7, 148 polymerization, 7, 144 reactions... 

The living polymerization of lactones, oxiranes, and thiiranes became also possible by improved preparation of the Al—Zn oxyalkoxides. These catalysts were first studied by Tsuruta 6) and by Vanderberg 7), and later by Teyssie 8 b). 

Stereoelective polymerization of enantiomerically unbalanced (i.e., partly resolved) mixtures of oxiranes and thiiranes has given suq)rising results (277, 318, 322). The stereoelectivity ratio, r, is greatly dependent on the enantio-... 

The 3- and 4-membered cyclic sulfides, referred to as thiiranes (also episulfides) and thie-tanes, respectively, are easily polymerized by both cationic and anionic initiators, such as... 

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