S. Hadjikyriacou et R. Faust, Living coupling reaction in living cationic polymerization. 3. Coupling reaction of living polyisobutylene using bis(furanyl) derivatives, MACROMOLEC, 33(3), 2000, pp. 730-733
Living coupling reactions of living polyisobutylene (PIB) with bis(furanyl)
compounds, 2,2-difurylmethane (DFM), 2,5-bis(2-furylmethyl)furan (bFMF), 2
,2-difurylpropane (DFP), and 2,5-bis(2-furyl-2-propyl)furan (bFPF) were inv
estigated in the presence of TiCl4 as Lewis acid in hexanes/CH3Cl 60/40 and
40/60 (v/v) at -80 degrees C and with bFPF in conjunction with BCl3 in CH3
Cl at -40 degrees C. The products obtained with DFM and bFMF were slightly
colored most probably due to alpha-hydride abstraction and the development
of conjugated structures. DFP and bFPF, lacking alpha-hydrogens, yielded co
lorless products. In hexanes/CH3Cl 60/40 (v/v), coupling was very slow and
incomplete after 2 h with DFM and DFP, which was ascribed to deactivation o
f the second furanyl ring after monoaddition. Coupling was faster with bFMF
; however, the coupling efficiency was only 85% after 2 h due to some side
reactions that consumed bFMF. Coupling was rapid and quantitative with bFPF
in the presence of TiCl4 in hexanes/CH3Cl 60/40 (v/v) at -80 degrees C. In
creasing the solvent polarity to hexanes/CH3Cl 40/60 (v/v) further increase
d the late by 2-fold. Efficient, albeit slow, coupling was also achieved wi
th bFPF in CH3Cl at -40 degrees C in the presence of BCl3. The mechanism of
the coupling reaction was investigated in the presence of TiCl4 in hexanes
/CH3Cl 60/40 (v/v) at -80 degrees C by quenching the reaction mixture with
tributyltin hydride after complete coupling had been achieved. Identificati
on of the product structure by H-1 NMR spectroscopy verified the formation
of stable dications upon coupling and confirmed that this reaction is a liv
ing coupling reaction.