Ring-opening polymerization cyclic compounds

The key initiation step in cationic polymerization of alkenes is the formation of a carbocationic intermediate, which can then interact with excess monomer to start propagation. We studied in some detail the initiation of cationic polymerization under superacidic, stable ion conditions. Carbocations also play a key role, as I found not only in the acid-catalyzed polymerization of alkenes but also in the polycondensation of arenes as well as in the ring opening polymerization of cyclic ethers, sulfides, and nitrogen compounds. Superacidic oxidative condensation of alkanes can even be achieved, including that of methane, as can the co-condensation of alkanes and alkenes. 

Formation of polymer chains or networks from these compounds can be conceived either as a ring-opening polymerization process or a polyreaction involving exo-cyclic functional groups. 

Here, lipase-catalyzed ring-opening polymerization of cyclic compounds giving polymers other than polyesters is described. l,3-Dioxan-2-one, six-membered cyclic carbonate, was polymerized in the presence of lipase catalysts (Fig. 13)... 

Kobayashi, S. and T. Saegusa, Cyclic 1,3-Oxaza Compounds, Chap. 11 in Ring-Opening Polymerization, Vol. 2, K. J. Ivin, and T. Saegusa, eds., Elsevier, London, 1984. 

Cyano compounds liquid crystals, 12, 278 in silver(III) complexes, 2, 241 Cyanocuprates, with copper, 2, 186 Cyano derivatives, a-arylation, 1, 361 Cyanosilanes, applications, 9, 322 Cyclic acetals, and Grignard reagent reactivity, 9, 53 Cyclic alkenes, asymmetric hydrosilylation, 10, 830 Cyclic alkynes, strained, with platinum, 8, 644 Cyclic allyl boronates, preparation, 9, 196 Cyclic allylic esters, alkylation, 11, 91 Cyclic amides, ring-opening polymerization, via lanthanide catalysis, 4, 145... 

Sulfur is an interesting atom because of the specific characteristics of the simple substance and compounds containing sulfur. Further, their functions are indispensable for current technologies. Studies on sulfur compounds are valuable not only in chemistry but also in biochemistry as well. Many cyclic monomers containing sulfur such as cyclic disulfides, thiiranes, thietanes, and arene dithiols were reported to form cyclic polymers by the ring-opening polymerization. The natural source of cyclic polymers is believed to be liquid, elemental sulfur [177-179]. 

Table 5-3. Examples of cyclic compounds that undergo ring-opening polymerization.

It must be considered that silyl triflates are not stable in THF for an extended time, because they can initiate the cationic ring-opening polymerization (ROP) of cyclic ethers. Therefore, the silyl triflate (in diethyl ether) is added in drops to the (aminosilyl)lithium compound dissolved in THF. The reaction proceeds very quickly, and ROP of THF is not observed under these conditions. The trisilanes la - Ic can be converted by reaction with triflic acid into the silyl bis (triflates) 2a - 2c. These compounds are precursors for further chain elongation. The reaction with (diethylamino)-diphenylsilyllithium leads to the pentasilanes 3a - 3c. The reaction of bis(diethylamino)phenylsilyl-lithium [9] with silyl triflates proceeds analogously. The formation of the disilane 4 is shown in Scheme 2 as an example. Conversion with triflic acid and chain elongation with LiSiPh2(NEt2) leads to the branched tetrasilane 6. 

In the course of time it appeared that many olefinic substrates could undergo this reaction in the presence of a transition metal compound, such as substituted alkenes, dienes, polyenes, and cyclic alkenes, and even alkynes. Calderon et al. were the first to realize that the ring-opening polymerization of cycloalkenes, which they observed with their tungsten-based catalyst system [4], and the disproportionation of acyclic olefins are, in fact, the same type of reaction. They introduced the more general name metathesis [2], The metathesis reaction has now become a common tool for the conversion of unsaturated compounds. In view of the limited space this intriguing reaction is reviewed only briefly more information can be found in a detailed and extensive monograph [5]. 

Ring-opening polymerization of cyclic ethers and lactones has been a major area of research in Lewis acid-promoted reactions. In particular, aluminum compounds have been investigated in depth not only because of their high oxophilicity and ability to initiate polymerization but also because of their commercial availability and low cost. 

The ring-opening polymerizations of heterocyclic compounds are important, not least because of the number of commercial polymers produced in this way. The best-known examples include Nylon 6, which is produced from e-caprolactam as shown in Scheme 16 poly(ethylene oxide) produced by ring-opening polymerization of ethylene oxide (or oxirane), a route to which is described in Protocol 14 (Scheme 17), and poly(dimethylsiloxane) which is formed from a cyclic tetramer produced on hydrolysis of dimethyl-silyldichloride in a way similar to that described in Protocol 15. 

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