142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

18 B. Charleux, R. Faust
initiators for the living cationic polymerization of IBVE in conjunction with either
ZnCl 2 , or EtAlCl 2 in the presence of a base such as 1,4-dioxane.
The polymerizations of IBVE were carried out with the multifunctional initiators
8 and 9 in conjunction with EtAlCl 2 and 1,4-dioxane (10 vol.% to the solvent)
in n-hexane or toluene at 0 °C. To determine their initiating efficiency, the
polymerization rates observed with these multifunctional initiators were compared
with those observed with their respective monofunctional counterparts at
the same concentration of initiating functions. For each system, the polymerization
rates were found to be in good agreement indicating that the concentration
of growing species was identical, i.e., all functions have initiated. The MWs, determined
by SEC with polystyrene calibration, were about three times higher
with the trifunctional initiators compared to the monofunctional analog, and
the polymers exhibited narrow MWD. For instance, initiator 8 at 3.5 mmol l –1
concentration was used to polymerize IBVE at a concentration of 0.76 mol l –1 .
SEC analysis of the polymer gave apparent M n =23,300 g mol –1 (M w /M n =1.08) at
complete conversion; using the monofunctional analog at 10 mmol l –1 concentration
the polymer had M n =8100 g mol –1 (M w /M n =1.06). It was also found that
additional feeds of monomer after complete conversion of the first monomer increment
led to a linear increase of MW in direct proportion with conversion. After
quenching with methanol or sodiomalonic ester, the number average end
functionality (F n), calculated using 1 H NMR spectroscopy based on integration
of characteristic peaks of terminal function and initiator residue, was found to
be close to three. Hydrolysis of the ester core of the star polymer obtained with
initiator 9 led to a poly(IBVE) with M n one third of the star itself and the MWD
remained narrow. Moreover, 1 H NMR spectrum of the isolated arms indicated
the expected structure with the hydroxyl terminal function. From this experimental
evidence, the authors concluded that well-controlled three arm stars of
poly(IBVE) were synthesized for the first time with this monomer. The star pol-
(8)
(9)