Influence of various proton traps on the bifunctional cationic polymerization of chloroethyl vinyl ether mediated by α-iodo ether/zinc dichloride
Résumé
The synthesis of relatively high molar mass telechelic poly(chloroethy1 vinyl ether)s (PCEVE) via bifunctional initiation of the "living" cationic polymerization of CEVE was examined in the absence and in the presence of various proton traps. In the absence of a proton trap, a monofunctional initiation involving hydrogen iodide (HI), formed by partial hydrolysis of trimethylsilyl iodide (TMSI) by adventitious water, occurred concurrently to the main bifunctional process. The addition of sterically hindered aromatic amines leads to complete inhibition of the polymerization due to the formation of a complex between the aromatic amines and ZnC12. In the presence of trialkylaluminium as HI trapping agent, monofunctional initiation is totally suppressed and a clean bifunctional polymerization takes place. Telechelic PCEVE of r P n up to 300 with narrow molar mass distribution were synthesized. However, in the presence of these additives, a slow ligand exchange between AIR3 and ZnC1, takes place, decreasing the rate of polymerization. For polymers with high r P n (>300), the increasing amount of trialkylaluminium required to totally suppress the formation of monofunctional polymer results in a chain coupling process during the deactivation step. This reaction limits the clean synthesis of high molar mass bifunctional PCEVE.