Alkali Metal Alcoholate and Phenolate Active Sites

1 Alkali Metal Alcoholate and Phenolate Active Sites 

Eor alkali metal compounds used as initiators, the active species of polymerization was shown to be an alkali metal alcoholate for the aliphatic cyclic carbonates [24] and an alkali metal phenolate for the aromatic cyclic carbonates [29]. The time required to shift from kinetic control to thermodynamic control is about a few minutes when the polymerization of aliphatic cyclic carbonates is performed at 25 °C in toluene solution. The larger the alkali-metal counterion, the faster the polymerization and the smaller the selectivity parameter, = kp/kb- 

The aromatic cyclic carbonates based on bisphenol-A or substituted o,o -methy-lenebisphenols were polymerized in tetrahydrofuran (THE) and in toluene with potassium-based initiators, for example potassium naphthalene at 60 C and 25 C, respectively [29]. In a rapid reaction the polymer was obtained in equilibrium with cycHc oligomers. However, with Hthium-based initiators the chain propagation does not occur under these mild conditions, due to the low nucleophUidty of the active species, which arises from the covalent character of the Hthium phenolate hnkage. 

The polymerization of DTC with polymeric initiators on the basis of poly(THF) was performed with different alcoholates as active species, and Li, K, or BU4N counterions, in toluene solution at ambient temperature. The polymer yields were 80-90% with a PDl of 1.3 M /Mn 1.7. Compared to the polymeric initiators based on P EO, the polymerization of DTC proceeded more slowly [27], a fact which could be explained by the reduced solvation abUity of PTHF with respect to the counter ions, as compared to PEO. 

1 Metal-Free Active Sites Site Transformation from Croup Transfer Polymerization to Anionic Metal-Free Polymerization 

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