Oxanorbornene and its derivatives

Derivatives of acyclic olefins can be used as chain-transfer agents in these polymerizations. The most effective are those with a terminal double bond. For example, in the ROMP of 181 catalyzed hy [Ru(H20)6](0Ts)2, the transfer constant k,r/kp) for CH2=CHCH2CH20H is 0.21 (see Ch. 15). The size of the polymer particles produced by emulsion polymerization of 181, using RuCls with a nonionic surfactant is of the order of 0.03 fim (Lu 1993b). 

In many cases, side reactions are liable to occur during the ROMP of these monomers, for example, esterification and trans-esterification when the ROMP of carboxylic acids, anhydrides, or esters are carried out in solvents containing alcohols, or hydrolysis when carried out in water (Drent 1991 Lu 1993a, 1994). Retro-Diels-Alder reactions can also be a problem. Thus, although 199 is cleanly polymerized to high conversion by [Ru(H20)6](0Ts)2 under mild conditions (55°C), its endo-isomer fails to polymerize because the retro-Diels-Alder reaction produces N-methylmaleimide, which complexes with the catalyst and puts it out of action. The exo-N-phenyl analogue is likewise unable to polymerize (Hillmyer 1992). 

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Table 20 Selected examples for the polymerization of 7-oxanorbornene and its derivatives. 

H) Emulsion and miniemulsion polymerization Emulsion-type polymerizations for ROMP of norbornene and its derivatives were first reported using hydrates of Ru, Ir, and Os four decades ago. " However, polymerization rates were very low. ROMP using water-soluble ruthenium carbene complexes as catalysts was used to polymerize functionalized 7-oxanorbornenes not only in water and methanol, but also in aqueous emulsions. Gationic water-soluble aliphatic phosphines were used in the synthesis of the ruthenium carbene complexes. The polymer polydispersity was low (1.1-1.3), although few details of the dispersed phase polymerization were reported. 

The treatment of 23 with methyllithium in the presence of furan gave rise to the tetracyclic product 26, which is obviously a [4 + 2]-cycloadduct of furan to the 1,2-cyclopentadiene derivative 25 [27]. The feature that the oxanorbornene system of 26 carries its saturated substituent in the endo-position is analogous to the [4 + 2]-cycloadducts of furan to all six-membered cyclic allenes (see Section 6.3). Balci et al. [36] also provided evidence for the generation of l-phenyl-l,2-cyclopentadiene. They postulated this species to be an intermediate in the reaction of l-phenyl-2-iodocydo-pentene with potassium tert-butoxide in benzene at 240 °C, which resulted in the formation of 1-phenyl- and 1,2-diphenylcyclopentene. Both products were considered as evidence in favor of the diradical nature rather than the allene structure of 1-phe-nyl-1,2 -cyclopentadiene. 

ROMP and ROM are the two most frequently used methods in aqueous media. It was shown that the activity of the Ru catalyst is increased in the presence of small amount of water in the ROMP of 7-oxanorbornene derivatives. The most effective precursor was the aqua complex [Ru(H20)6](tos)2. After the polymerization was completed the aqueous catalyst phase could be reused and the catalytic activity increased in the subsequent reaction (Figure 26). An aqua-ruthenium (ii) olefin complex was isolated with higher catalytic activity than the adduct formed from the [Ru(H20)6](tos)2-complex and the 7-oxanorbornene derivative it was suggested that the Ru-carbene complex was formed from this compound. 

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