Influence de la temperature sur les associations moleculaires et sur la polymerisation de l'acide acrylique en solution

Infra-red spectra of pure acrylic acid and solutions of monomer in toluene indicate that increasing the temperature from 20 to 60° displaces the equilibrium of H-bonded species from cyclic dimer to open oligomer. Viscosity measurements on the same solutions confirm this conclusion. In methanol solutions. alcohol-alcohol and alcohol-acid associations are found together with the acid-acid associations and the interpretation of the results is extremely difficult. Polymerization kinetics are directly influenced by the shift of association equilibria. In hexane, an increase in temperature results in a sudden increase in reaction rate as the linear oligomeric structures appear in the solution. In methanol increase in temperature reduces the kinetic anomalies observed at 20 and the polymerization no longer exhibits any stereospecificity. At the same time, a chain transfer process sets in. These various results confirm the earlier assumption of an assisted propagation step occurring in auto-associated aggregates of acrylic acid.