Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Esters of diacids and oligo(carboxylic acid)s substituted in α-position with Li, Na, or K (models of the propagation site in the anionic polymerization of methyl methacrylate (MMA)) were prepared, and their IR spectra were recorded. In the range 1600 - 1800 cm-1, their absorption of the Mt+ group in benzene solution was reflected in a band between 1630 and 1645 cm-1, depending on the counterion. In the presence of THF or of tert-butoxide of the same alkali metal this band appears between 1626 and 1660 cm-1. Coordination of the more remote alkoxycarbonyl group (e.g., in γ-position) to the counterion is demonstrated by a band near 1712 cm-1; its absorbance is much lower in the presence of THF. In solution, the metalloesters undergo autocondensation, the rate of which increases dramatically with the number of monomeric units. Thus, in benzene at 25 °C ethyl 2-lithioisobutyrate is stable for more than a week, whereas the half life of dimethyl 2-lithio-2,4,4-trimethylglutarate (Li-dimer, 3b) is 〈24 h, and the Li-trimer (5a), Li-tetramer (5b), and Li-pentamer (5c) completely decompose in less than 4 min under these conditions. The decomposition may be slowed down by adding tert-butoxide of the same alkali metal. In THF the decomposition proceeds much more quickly. The properties of models used in this study are compared with those of the propagation site in the anionic polymerization of MMA.
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