Ring alternating copolymerizations

Abstract Development in the field of transition metal-catalyzed carbonylation of epoxides is reviewed. The reaction is an efficient method to synthesize a wide range of / -hydroxy carbonyl compounds such as small synthetic synthons and polymeric materials. The reaction modes featured in this chapter are ring-expansion carbonylation, alternating copolymerization, formylation, alkoxycarbonylation, and aminocarbonylation. 

Coates and coworkers have carried out kinetic studies of the alternating copolymerization of CHO and C02 catalyzed by several of the P-diiminate zinc derivatives [29]. These authors have proposed a bimetallic mechanism to be operative, which is consistent with their experimental observations, including the large differences in activity noted for a series of structurally closely related catalysts. It was proposed that one zinc center would coordinate and activate the epoxide substrate, while the second zinc center would provide the propagating carbonate species to ring-open the epoxide. This proposal is represented by the transition state depicted in Figure 8.3a. 

Spontaneous alternating copolymerizations of two cyclic phosphorus compounds, 2-phenyl-l,3,2-dloxaphospholane 11 and 2-phenoxy-1,3,2-dloxaphospholane 20, with several electrophilic monomers were discussed. As the electrophilic monomers, /3-proplolactone 13, 3-hydroxypropanesulfonlc acid lactone (propane-sultone) 15, acrylic acid 16, acrylamide 17, acrylate were sucessfully copolymerized with 11. At temperatures lower than those of copolymerization, the combinations of 11—13, 11—16, 11—-17 and 11—acrylate produced trioxyphosphorane derivatives having spiro-ring structures, which were significant in two... 

We previously showed that well-defined, structurally characterized P-diiminate (BDI) zinc complexes (Figure 1) catalyze the ring-opening polymerization of cyclic esters (22,23) and the alternating copolymerization of... 

A special case of stereoelectivity has been encountered in polymerizing a racemic monomer with an optically active one. Minoura et al. (158) carried out the ring-opening copolymerization of propylene oxide with d-camphoric acid anhydride using diethyl zinc and triethyl amine as catalyst. It was found that the products were alternating copolymers which were optically active. The propylene oxide recovered from the copolymerization system was also optically active. An attempt to incorporate preferentially in a polyamide chain one of the optical antipodes of trans-cyclopropane-1,2-dicarbonyl chloride, by polycondensing this racemic monomer with optically active 1,2-propylene diamine failed (159). 

Schiff base catalyst was also active in TMC polymerization. Moreover, chromium(III) salen derivatives in the presence of anionic initiators have been shown to be very effective catalytic systems for the alternating copolymerization of oxetane and carbon dioxide to provide the corresponding PC with a minimal amount of ether linkages. The best results were achieved for the salen ligand with tert-butyl groups in the 3,5-positions of the phenolate rings and a cyclohexylene backbone for the diimine along with an azide ion initiator (Scheme 57). 

Scheme 27 A ring-opening-closing alternating copolymerization.

The elucidation of the mechanism of ring-opening copolymerization of cyclic urea and carbonates offered opportunihes to study the general applicability of this mechanism to the copolymerizahon of tetramethylene urea with other monomers. The five-membered lactone, y-butyrolactone, is a readily available and cheap monomer, which may barely be homopolymerized (see Chapter 11). The copolymerization of tetramethylene urea with y-butyrolactone in the presence of dibutyl-magnesium as catalyst in the melt at 100 °C resulted in an alternating poly(amide urethane) (M = 12 600gmoT M = 21000gmoT = 1.67) [64]. 

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) ... 

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