Polymérisation anionique de l'acroléine, 3. Analyse des microstructures par ¹H NMR et ¹³C NMR et mécanisme de polymérisation

Abstract

We have synthesized anionic polyacroleins using various initiators (naphthalene complex, tert-butyllithium) in different solvents (tetrahydrofuran, toluene). We have studied the 'H NMR and 13C NMR spectra of the polymers and assigned monomeric units and diads by comparison with spectra of four compounds corresponding to the different microstructure arrangements. By this method, we have clearly proved the presence of 1,4-as well as 3,4-and 1,2-units. But numerous cyclisations occur on the 1,2-units. Using only the 'H NMR method, a first estimation of the microstructure was obtained. I3C NMR gave further information and permitted the estimation of the (1 ,4-cis)/( 1 ,4-trans) ratio. Furthermore the presence of hydroxyl groups along the chains has also been established. A satisfactory determination of the 1,2-, 3,4-and 1,4-structure percentages of several polyacroleins has been obtained using 'H NMR and 13C NMR simultaneously. A mechanism of acrolein polymerization, based on two different living ends is proposed. The microstructure indicates the existence of several complexation phenomena. When the living end/metal and monomer/metal complexations are weak (with Na' e.g.), the polymer consists mainly of 1,4-and 3,4-units. On the other hand, with Li', the microstructure has a high 1 ,2-content. Moreover, the living end/Li+ complexation would decrease with the chain length, because of the increasing attraction of the cation by the other complexing sites on this chain.

Ionic oligomerization of acrolein in water

“…Acrolein anionic polymerization under standard air-free conditions can be initiated by several metalorganic or basic compounds such as organolithium, lithium organocuprates, ammonia, tert-phosphines and aromatic amines. [25][26][27][28] The polymerization reaction proceeds across the carbonyl function via (3,4) addition and across the aldehyde and vinyl functions by (1,4) addition (Scheme 1). 29 According to the reactions conditions (temperature and solvent), the microstructure of polymers obtained with these catalysts, i.e.…”

H-type Zeolite-Catalyzed 1,4-Addition of Benzene Derivatives to Labile Acrolein

“…33 The expected signals for the polymeric by-products of acrolein were not observed by 13 C DD/MAS NMR ( Figure 3a) as well as 13 C CP/MAS NMR. 34 We concluded that a part of the acrolein monomer was still present in the zeolite pores, but that it was difficult for the 13 C MAS NMR technique to detect and quantify the formation of acrolein polymers at such a low concentration level.…”