Anionic polymerization propylene sulfide

Anionic polymerization of alkylene sulfides was extensively studied by Sigwalt and collaborators. In contrast to propylene oxide, anionic polymerization of pro-... 

The range of monomers that can be incorporated into block copolymers by the living anionic route includes not only the carbon-carbon double-bond monomers susceptible to anionic polymerization but also certain cyclic monomers, such as ethylene oxide, propylene sulfide, lactams, lactones, and cyclic siloxanes (Chap. 7). Thus one can synthesize block copolymers involving each of the two types of monomers. Some of these combinations require an appropriate adjustment of the propagating center prior to the addition of the cyclic monomer. For example, carbanions from monomers such as styrene or methyl methacrylate are not sufficiently nucleophilic to polymerize lactones. The block copolymer with a lactone can be synthesized if one adds a small amount of ethylene oxide to the living polystyryl system to convert propagating centers to alkoxide ions prior to adding the lactone monomer. 

Kinetics of anionic ring-opening polymerization has hitherto been quantitatively studied and gave for two monomers, namely ethylene oxide [IS,12] and propylene sulfide [8.20]. Studies on these systems revealed that the living conditions can be achieved, facilitating quantitative determination of rateconstants of propagation on various kinds of ionic growing species. 

These ligands form extremely stable cation inclusion complexes, called cryptates, In which the cation Is completely surrounded by the ligand and hidden Inside the molecular cavity, and this leads to a considerable Increase of the interionic distance In the ion pairs. It has been shown that such ligands have a marked activating effect on anionic polymerizations (4,5,6). Moreover, the aggregates are destroyed and simple kinetic results have been obtained In the case of propylene sulfide (7,8,9). ethylene oxide (9,10,11) and cycloelloxanes (12) polymerizations. Though the... 

Propagation Constants of Free Ions and Ion Pairs for the Anionic Polymerization of Propylene Sulfide in THF at -30 C... 

Figure 2. Plot of log k vj. the reciprocal of interionic distance parameter of ion pairs for the anionic polymerization of propylene sulfide at —30°C in THF ( ) ...

In conclusion, it has been shown that use of cryptates for the anionic polymerization of heterocyclic monomers leatis to a tremendous increase of the rates of polymerization. There are two main causes to the higher reaction rates observed with cryptates. The first one is a suppression of the association between ion pairs in the non polar media, and the second one is the possibility of ion pairs dissociation into free ions in ethereal solvents like THP or THF. By this way, it has been possible to make detailed studies of the propagation reaction for propylene sulfide, ethylene oxide, and cycloslloxanes. 

With Na+, as a cation, the activation energies for the anionic polymerization of acrolein and propylene sulfide (11) are approximately the same. On the other hand, with Li+, it is impossible to compare the acrolein activation energy with the same monomer or another polar monomer because no result is found in the literature. Moreover, for the acrolein polymerization, (Raj u+) lower than ( > +). 

In the anionic polymerization there are three monomers only that have been studied in more detail, namely ethylene oxide, propylene sulfide, and B-propiolactone. Some... 

Anionic polymerization. In anionic polymerization ethy-lene oxide, propylene sulfide or their corresponding... 

In a practical sense the hydrocarbon monomers that work best in anionic systems are styrene, a-methylstyrene, p-(tert-butyl)styrene, butadiene, isoprene, 2,3-dimethyIbutadiene, piperylene, stilbene, and 1,1-diphenylethylene. The latter two monomers give rise to alternating copolymers with other dienes but do not homopolymerize. Among the polar monomers (C) that can be polymerized are such monomers as 2-vinyIpyridine, pivalolactone, methacrylonitrile, methyl-methacrylate, ethylene oxide (not with Li-counterion), ethylene sulfide, and propylene sulfide. However, polymerization of many of these polar monomers suffers from side reactions and complicating termination or transfer reactions not present in the... 

In the polymerization of propylene sulfide and 1,2-butylene sulfide mainly tetra-mers were observed. Cycles were formed mostly during the slow degradation process that followed rapid polymerizations. Degradation can also be induced by adding cationic initiators to polymer prepared by other mechanisms, e.g. by anionic processes. Thus, poly(trans-2,3-butene sulfide) is rapidly degraded to equimolar amounts of 3,5,6,7-tetramethyl-l,2,5-trithiacycloheptane and trans-butene 47). Poly(cis-2,3-butene sulfide) forms, however, a mixture of tetramer, trithiacycloheptane derivative and cis-butene 47 . If one is forced to use cationic processes for the synthesis of poly-sulfides, the reaction conditions should be controlled to avoid macrocyclization. If cyclic products are desired, the kinetics of their formation should be studied to determine optimum yields. 

PREPARATIVE TECHNIQUE Poly(propylene sulfide) can be prepared by ring-opening polymerization, using anionic, cationic, and coordinate catalyst. Anionic and cationic systems give an amorphous atactic polymer, while coordinate catalytic system, such as cadmium salts, give an isotactic or crystalline polymer. ... 

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. 

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 ... 

Then, the thiolate anion polymerizes the excess propylene sulfide ... 

Although the reactivity increase caused by crown ethers and cryptands in anionic polymerizations has already found a wide range of application, more details have been reported and a number of questions concerning the type and the behavior of the different species present, both in the initiation and in the propagation steps, have been clarified by, for example, kinetic studies [235], Special polymerization reactions that were effected in the presence of crown compounds are those starting with butadiene, propene, styrene, 2-vinyl pyridine, ethylene oxide, propylene sulfide, isobutylene sulfide, methyl methacrylate, p-propyllactone, or e-caprolactone as monomers and alkali metals as initiators [238-246],... 

Polymerization of propylene sulfide in the presence of carbonates and zinc, cadmium, or alkaline thiolates produces oligosulfides with —HS end groups [22]. It was found that at anionic polymerization of propylene sulfide, chains with regular structure of the type —(CHj—CHfCHj)—S—S) — are obtained. In the catalytic BuLi-LiOR system, propylene sulfide polymerization take place according to the following mechanism [I] ... 

Boileau, Kaempf, Schue and coworkers have studied the cryptate mediated anionic addition polymerization of several systems including ethylene oxide [38], propylene sulfide [39-40], isobutylene sulfide [40], isoprene [38], methyl methacrylate [38], hexamethyl trisiloxane [40], e-caprolactone [41], styrene [38, 40, 41], ct-methylstyrene [41], 1,1-diphenylethylene [41] and /3-propiolactone [42]. The polymerization of the latter compound induced by dibenzo-18-crown-6 complexed sodium acetate has also been reported [43]. In general, it was found that the polymer-... 

The parent compound, thiirane (ethylene sulfide), produces a crystalline polymer with a melting point of 205 °C that is insoluble in most solvents.As a consequence, the polymerizations of this monomer are heterogeneous and mechanistic studies are difficult. The most studied monomer is methylthiir-ane (MT) often referred to as propylene sulfide. However, other substituted thiiranes have also been described extensively in the literature. The polymerizations can occur by cationic, anionic, coordinative, and monomer insertion mechanisms. 

Chain transfer to monomer is much less prevalent for polymerizations with most of the anionic coordination initiators. Much higher molecular weights are thus possible in these polymerizations. For example, molecular weights of the order of 10 are reported for propylene polymerization by an initiator derived from diphenyltin sulfide and bis(3-dimethylaminopropyl)zinc. 

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