Copolymerization of cyclohexene oxide and

However, there are numerous reported instances of stereocontrol by a site-control mechanism involving chiral metal catalysts. That is, Nozaki and coworkers first illustrated the asymmetric alternating copolymerization of cyclohexene oxide and CO2 employing a chiral zinc catalyst derived from an amino alcohol (Fig. 2a) [13-16]. This was soon followed by studies of Coates and coworkers utilizing an imine-oxazoline zinc catalyst (Fig. 2b) [17]. Both investigations provided isotactic poly(cyclohexene carbonate) (Fig. 3) with enantiomeric excess of approximately 70%. 

Furthermore, size-exclusion chromatography (SEC) analyses generally reveal a bimodal distribution of molecular weights of the copolymers. Concomitantly, MALDI-ToF mass spectral measurements exhibit two sets of peaks corresponding to copolymer end groups of -OH and -X. For example, utilizing a (salen)CrCl/bis (triphenylphosphme)iminium chloride ([PPNjCl) catalyst for the copolymerization of cyclohexene oxide and carbon dioxide, the two copolymers illustrated in Fig. 6 were observed [26]. 

We have utilized somewhat less-effective optional approaches to copolymer purification with attendant catalyst recovery. One of these methods involved the replacement of the f-butyl substituents on the 5-position of the phenolate ligands with poly(isobutylene) (PIB) groups, as illustrated in Fig. 14 [39]. Importantly, this chromium(III) catalyst exhibited nearly identical activity as its 3,5-di-t-butyl analog for the copolymerization of cyclohexene oxide and carbon dioxide. The PIB substituents on the (salen)CrCl catalysts provide high solubility in heptanes once the copolymer is separated from the metal center by a weak acid. 

Table 8.1 Catalytic activity for the copolymerization of cyclohexene oxide and C02 in the presence of one equivalent of PPNX cocatalyst.3...

Copolymerization of cyclohexene oxide and CO2 proceeds with an immobilized chromium phorphyrin complex, although the molecular weight of the resulting copolymer 47 is limited to the oligomer level (Scheme 87). 

Figure 6. An example of a potential use of a switchabie solvent the copolymerization of cyclohexene oxide and CO 2- In the new route, after the polymer precipitate is removed by filtration, the ionic liquid is easily distilledfrom the Cr catalyst, and both the solvent and the catalyst are then recycled.

An optically active polycarbonate (271) has been synthesized by asymmetric synthesis copolymerization of cyclohexene oxide and CO2 with optically active Zn catalysts 272 and 273. " Through hydrolysis of the polymer giving 1,2-dihydroxycyclohexane, the absolute configuration was found to be R,R). The optical purity of the polymer was estimated to be 72% ee and 80% ee with the catalysts 272 and 273, respectively. 

SCHEME 24.13 Chiral zinc catalysts for the asymmetric, alternating copolymerization of cyclohexene oxide and CO2. 

Coates and coworkers recently reported the first syndioselective copolymerization of cyclohexene oxide and CO2 (Scheme 24.17). Using complex [rac-(salpr-t-Bu)CoBr] (18), poly(cyclohexene carbonate) was formed with 80% [r]-centered tetrads, as determined by C NMR spectroscopy. 

Nozaki, K. Nakano, K. Hiyama, T. Optically active polycarbonates Asymmetric alternating copolymerization of cyclohexene oxide and carbon dioxide. J. Am. Chem. Soc. 1999, 121,... 

Cohen, C. Thomas, C. Peretti, K. Lobkovsky, E. Coates, G. Copolymerization of cyclohexene oxide and carbon dioxide using (salen)Co(lII) complexes Synthesis and characterization of syndiotactic poly(cyclohexene carbonate). Dalton Trans. 2006, 237-249. 

Darensbourg DJ, Yarbrough JC, Ortiz C, Fang CC (2003) Comparative kinetic studies of the copolymerization of cyclohexene oxide and propylene oxide with carbon dioxide in the presence of chromium salen derivatives. In situ FTIR measurements of copolymer vs cyclic carbonate production. J Am Chem Soc 125 7586-7591... 

Lee K, Ha JJY, Cao C, Park DW, Ha C-S, Kim I (2009) Effent of complexing agents of double metal cyanide catalyst on the copolymerizations of cyclohexene oxide and carbon dioxide. Catal Today 148 389-397... 

Scheme 14 Binuclear magnesium complexes supported by phenol-bridged bis(a,a-diarylprolinol) ligands for the copolymerization of cyclohexene oxide and CO2 by Ding and coworkers [120]...

Poly(propylene carbonate) Propylene carbonate Scheme 23 Copolymerization of cyclohexene oxide and propylene oxide with CO2. 

Cui, D. M. Nishiura, M. Hou, Z. M. Alternating Copolymerization of Cyclohexene Oxide and Carbon Dioxide Catalyzed by Organo Rare Earth Metal Complexes. Macromolecules 2005, 38, 4089 095. 

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