Efficiency, oxirane polymerization

Organotin compounds with the general formulae RSnX3, R2SnX2, R3SnX and RSnOOH (R = alkyl or aryl and X = Cl, Br or J) are efficient catalysts for the polymerization of oxiranes 73). 

Organometallic compounds asymmetric catalysis, 11, 255 chiral auxiliaries, 266 enantioselectivity, 255 see also specific compounds Organozinc chemistry, 260 amino alcohols, 261, 355 chirality amplification, 273 efficiency origins, 273 ligand acceleration, 260 molecular structures, 276 reaction mechanism, 269 transition state models, 264 turnover-limiting step, 271 Orthohydroxylation, naphthol, 230 Osmium, olefin dihydroxylation, 150 Oxametallacycle intermediates, 150, 152 Oxazaborolidines, 134 Oxazoline, 356 Oxidation amines, 155 olefins, 137, 150 reduction, 5 sulfides, 155 Oxidative addition, 5 amine isomerization, 111 hydrogen molecule, 16 Oxidative dimerization, chiral phenols, 287 Oximes, borane reduction, 135 Oxindole alkylation, 338 Oxiranes, enantioselective synthesis, 137, 289, 326, 333, 349, 361 Oxonium polymerization, 332 Oxo process, 162 Oxovanadium complexes, 220 Oxygenation, C—H bonds, 149... 

The evolution of nitrogen on photolysis of the aryIdiazonium salts appears to have limited the use of these systems to thin film applications such as container coatings and photoresists (23). Other efficient photoinitiators that do not produce highly volatile products have been disclosed (24-27). These systems are based on the photolysis of diaryliodonium and triarylsulfonium salts. Structures I and II, respectively. These salts are highly thermally stable salts that upon irradiation liberate strong Bronsted acids of the HX type (Reactions 43 and 44) that subsequently initiate cationic polymerization of the oxirane rings ... 

High molecular weight polyECH as well as its copolymers with ethylene oxide (EO) are commercial products. Their production is based on the discovery made by Van-denberg4 5 who first observed that some modified alkyl aluminiums are efficient initiators, giving high molecular weight products in the polymerization of various oxiranes. 

Despite a number of investigations, the efficient synthesis of co-epoxide-functionalized polymers in hydrocarbon solution with lithium as counterion at room temperature had not been reported. Takenaka et developed an efficient synthesis of epoxide-functionalized polystyrenes and poly-isoprenes by terminating the corresponding living polymeric anions with (2-bromoethyl)oxirane at -78 °C in THE as shown in eqn [27]. Termination of either PSLi or PlLi by inverse addition to 2-3 equivalents of (2-bro-moethyl)oxirane reportedly produced the corresponding epoxy-functionalized polymers in quantitative yields as determined by NMR and TLC-FID chromatography. However, the requirements of -78 °C and THF as solvent limit the usefulness of this procedure. 

There are three t)q)es of eompositions that eure by eationie meehanism. One of them uses aryldiazonium salts to initiate the reaetion. The seeond one utilizes onium salts and the third one organometallie eomplexes. The most prominent ones are those that eure with the aid of onium salt photoinitiators. Many cationic curable compositions consist of mixtures of compounds with oxirane rings. They may also be mixtures of vinyl ether. In addition, some compositions contain both, epoxides and vinyl ethers. More recent compositions might also include silicone based monomers with epoxide groups. Thus, Crivello and Lee described a synthesis of a series of silicon-epoxy monomers that undergo rapid and efficient photoinitiated cationic polymerizations. Such compounds can be prepared by direct hydrosilylation of olefmic epoxides. 

Naturally, anionic polymerization is not compatible with H-bonding moieties, thus requiring efficient modification after the polymerization reaction (Ilhan et al., 2001 Schadler et al., 1998). An excellent example (Karatzas et al, 2006) of an efficient postmodification method was presented starting from living PS-PI anions, which was quenched by only one unit of oxirane, furnishing the hydroxy-telechelic PS-PI BCP (15). This in turn was reacted with the isocyanate (16), attaching the ureidopyrimidone moiety to the final polymer (17). 

Glycolates were found to be very efficient initiators in the polymerization of thiiranes and oxiranes [17]. The reaction of glycolysis of organometallic compounds is given in Figure 5. Towards a given hydroxy compound the reactivity of the organometallic derivatives follows the order... 

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