Living coupling reaction in living cationic polymerization. 3. Coupling reaction of living polyisobutylene using bis(furanyl) derivatives

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.