Novel approach to well‐defined polyester by living anionic alternating copolymerization of ethylphenylketene with 4‐methoxybenzaldehyde

Abstract

A living anionic alternating copolymerization of ethylphenylketene (EPK) with 4-methoxybenzaldehyde (MBA) was achieved. When n-butyllithium was added to a mixture of EPK and MBA in tetrahydrofuran at Ϫ40°C in the presence of an excess amount of lithium chloride, the copolymerization of these monomers proceeded via complete 1:1 alternating manner to afford the polymer with a narrow molecular weight distribution. A linear relationship was observed between the molecular weight and the monomer/initiator ratio, keeping a narrow molecular weight distribution. The structure of the obtained polymer was determined to be a polyester by IR spectroscopy together with the reductive degradation of the polymer by lithium aluminum hydride, which quantitatively afforded the corresponding diol to the repeating unit of the expected polyester structure. Both conversions of EPK and MBA agreed to a first-order kinetic equation with linear evolution between the molecular weight and conversion. These observations along with the successful results in two-stage polymerization indicate that the present copolymerization proceeded through a living mechanism.

Polyesters

“…The reaction does not take place with sterically hindered aldehydes. The anionic copolymerization of ketenes with aldehydes 393,394 or ketones 395 is a synthetic method allowing the preparation of sterically hindered polyesters which cannot easily be prepared by conventional ways. Thus, dimethylketene copolymerizes with aromatic aldehydes, such as benzaldehyde, in the presence of anionic initiators (e.g., BuLi or NaOEt), yielding polyesters with stereoregular structure 393 (Scheme 2.44).…”

Alternating Copolymerization of Ethylphenylketene with Benzaldehyde: Solvent- and Additive-Controlled Stereospecific Formation of Polyester

“…The obtained polymer was soluble in THF and CHCl 3 and was insoluble in MeOH. The structure of the resulting polymer was confirmed to be polyester 1 by its strong IR absorption at 1737 cm -1 . , Treatment of the polymer with lithium aluminum hydride in refluxing THF resulted in reductive degradation of the ester linkage to give the corresponding diol, 2-ethyl-2-phenyl-1-phenylpropanediol ( 2 ) in 92% yield, as expected from the ideal polyester structure formed by alternating copolymerization (Scheme ). The diol was obtained as a diastereomeric mixture, whose ratio was determined to be 69:31 (less polar diol 2a :more polar one 2b 9 ) by HPLC analysis.…”

“…We previously reported the living anionic alternating copolymerizations of ethylphenylketene (EPK) with aromatic aldehydes using n -butyllithium as an initiator . The resulting polyesters have two adjacent chiral centers in the repeat unit; however, the relative stereochemistry between them was not clarified.…”

The emerging utility of ketenes in polymer chemistry

“…(B)]. This living polymerization, initiated by alkyllithiums, was found to be perfectly alternating and produced a library of the structurally unique, highly‐substituted polyesters ( 11 ) …”