Synthesis,characterization, and diels–alder extension of cyclopentadiene telechelic polyisobutylene. IV. α,ω-Di(3-cyclopentadienylpropyldimethylsilyl)polyisobutylene

The synthesis and chain extension of polyisobutylene having nonfluxional terminal cyclopentadiene groups is described. The fluxional behavior of silylcyclopentadiene end groups was previously found to prevent Diels–Alder dimerization of the end groups. The incorporation of a propyl moiety between the silicon atom and the cyclopentadiene ring was found to prevent this fluxional isomerization. Polyisobutylene was synthesized having 3-cyclopentadienylpropyldimethylsilyl end groups with a functionality near 2.0. While thermal extension at 80°C resulted in threefold molecular weight increase, coupling with bisdienophiles yielded greater than tenfold molecular weight increases. The retro-Diels–Alder reaction of coupled end groups prevents the attainment of high-molecular-weight polymers at equilibrium.