Polymérisation de l'ε-caprolactone par des catalyseurs dérivés du bore

The cationic polymerization of ε-caprolactone catalyzed by boron derivatives, namely acyl fluoroborates, triethyloxonium fluoroborate (Meerwein's salt), boron trifluoride etherate and boron trifluoride was investigated. The acyl fluoroborates, especially the acetyl fluoroborate, produced high molecular weight polymers with fairly poor yields, whereas triethyloxonium fluoroborate gave a high yield of a rather low molecular weight polymer. The results were compared with those obtained with the two non-ionic catalysts. It seems that the acylium or ethylium group of the catalyst initiates the molecular chain and that the fluoroborate anion serves as catalyst and keeps the activity of the reaction site at the end of the growing chain. The mechanism is that of a polymerization without termination reaction (living-polymer type). However, according to the results of the kinetic study, this is true only in the case of acyl fluoroborates. The following relation between the viscosity and the number-average molecular weight of our samples was obtained: [η] = 1,25·10^?4M?_n^0,82.