Propylene oxide , ring-opening

With methyl oxirane, propylene oxide, ring opening is by cleavage of the less-substituted carbon-to-oxygen bond. Since the terminal oxyalkanol groups are still active, the polymerizations, as represented, are "living" polymerization reactions. However, there are termination side reactions that become particularly important at elevated reaction temperatures. 

Jacobsen and co-workers have used similar catalysts in the enantioselective opening of epoxide rings. Stereospecific hydrolysis with a cobalt acetate chelate can be used to resolve racemic epoxides.97 Propylene oxide was opened with trimethylsilylazide in the presence of a 7 7 chromium azide chelate catalyst to produce (5)-l-azido-2-trimethyl-siloxypropane in quantitative yield with 97% ee.98 Cyclohexene oxide was opened with benzoic acid in the presence of 1 mol% cobalt chelate catalyst to give the hydroxyben-zoate in 98% yield with 77% ee.99... 

Propylene oxide and other epoxides polymerize by ring opening to form polyether stmctures. Either the methine, CH—O, or the methylene, CH2—O, bonds ate broken in this reaction. If the epoxide is unsymmetrical (as is PO) then three regioisomers are possible head-to-tad (H—T), head-to-head (H—H), and tad-to-tad (T—T) dyads, ie, two monomer units shown as a sequence. The anionic and... 

With strong nucleophiles such as methoxide, ring opening follows an Sn2 mechanism. Examine the next to lowest-unoccupied molecular orbital (LUMO+1) for propylene oxide. On which carbon is it most heavily concentrated Is this also the least crowded carbon (Examine a spacefilling model for propylene oxide.) What should be the product of Sn2 addition ... 

The only known instance of ring-opening polymerization with these compounds is also the only report on the successful polymerization of 2,5-dihydrofuran74 in which this compound was cationically copolymerized with epichlorhydrin (rx 0, r2 0), propylene oxide (r, 0, r2 0) and 3,3-bischloromethyl oxacyclobutane (/ ] 0, r2 = 1.6). It was shown that all the copolymers obtained possessed a certain degree of unsaturation which was attributed to the presence of open units from 2,5-dihydrofuran. Thus, for example the alternating copolymer with epichlorhydrin had the following structure (IR spectra, Cl content. C=C analysis) ... 

Co/Zn double metal cyanide catalyzed ring-opening polymerization of propylene oxide effect of cocataiysts on polymerization behavior... 

The polymerization of (-l-)-propylene oxide also belongs to this class since the opening of the three-member ring occurs mainly at the primary carbon... 

We have reported a gas phase and solution phase study comparing mono-and dinuclear CF" complexes as catalysts for the ring opening polymerization of propylene oxide. (Adapted from Schon et al., 2004)... 

Based on the landmark studies of Jacobsen and coworkers, who employed chiral (salen)CoX complexes for the asymmetric ring opening and kinetic resolution of aliphatic epoxides [18-20], Lu and coworkers synthesized highly isotactic copolymer from rac-propylene oxide and carbon dioxide (Scheme 5) [21]. 

Scheme 9 Ring-opening pathways for the terpolymerization of propylene oxide and cyclohexene oxide with CO2...

In 1963, Heck reported the ring opening of propylene oxide by the carbonylating reagent tetracarbonylhydridocobalt(I) in the presence of carbon monoxide, which results in a stable acyl cobalttetracarbonyl compound (Fig. 15). However, no polymeric products were reported, which would result from multiple ring opening and CO insertion processes [58, 59]. 

The ring-opening polymerizations of cyclic monomers such as propylene oxide... 

The polymerization of an unsymmetric epoxide such as propylene oxide involves the possibility of two different sites (at carbons 1 and 2 or a and (3) on the epoxide ring for the nucleophilic ring-opening reaction. Two different propagating species are then possible ... 

Several other types of monomers are capable of yielding stereoisomeric polymer structures. Ordered structures are possible in the polymerization of carbonyl monomers (RCHO and RCOR ) and the ring-opening polymerizations of certain monomers. Thus, for example, the polymers from acetaldehyde and propylene oxide can have isotactic and syndiotactic structures as shown in Figs. 8-3 and 8-4. 

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