RbC24and CsC24were allowed to react with isoprene, styrene or 1,3-butadiene. RbC24expanded slowly along the c-axis direction through contact with these unsaturated hydrocarbons. Monomer molecules are considered to be introduced into the interlayer of RbC24and polymerized. In the case of CsC24, isoprene was polymerized in a similar manner as RbC24and KC24, whereas the reactivity of styrene and 1,3-butadiene was low. The different reactivities are explained on the basis of the activity of polymerization initiators. The reactivity of monomers to polymerize in a certain GIC is in the following order: isoprene > 1.3-butadiene > styrene, which is the reverse order of reactivity recognized in the conventional polymerization.