Thermodynamic Study of the Ionic Polymerization of n-Butyraldehyde

Abstract

The polymerization of n-butyraldehyde, initiated in various solvents and in bulk with as well cationic (CF3SO3H, BF3:OEt2) as anionic (alkoxides) initiators, has been reinvestigated from -78° to +60°C by 1H, 13C NMR and UV spectrophotometry. The virtual equilibrium between the monomer and the cyclic trimer, previously reported for cationic initiation at high temperature has been confirmed over the whole temperature range. Anionic initiation in THF led to side reactions with formation of aldol derivatives. A monomer - polymer equilibrium was only observed in n-pentane. The thermodynamic parameters and ceiling temperatures have been determined for both anionic and cationic initiations. When using initiation by CF3SO3H and alkoxides, a crotonization took place for reaction temperatures above 5°C, with formation of 2-ethyl-hexenal. Using alkoxides, the polymer is rapidly formed in n-pentane at -78°C and slowly in THF only after initiation at -95°C. Using triflic acid, no polymer is observed even at -95°C in dichloromethane, but polymer is obtained in n-pentane at such a low temperature. Another way to get crystalline high polymer consists in condensing monomer vapor onto the anionic or cationic initiator solution cooled at T ≤ -50°C.