  In this paper, we studied the charmless $B_{c}\to VV$ ($V$ denotes the light
ground $\rm SU(3)$ vector meson) decays within the framework of QCD
factorization. In the evaluation, two different schemes for regulating the
end-point divergence are adopted. One (scheme I) is to use parameterization
model, which is usually employed in the QCD factorization approach; the other
(scheme II) is based on the infrared finite gluon propagator of Cornwall
prescription. It is found that, in the annihilation amplitudes, the end-point
divergence appears only in the power-suppressed corrections related to the
twist-3 distribution amplitudes of $V$-meson. The strength of annihilation
amplitudes evaluated in scheme II is generally larger than the one in scheme I.
Numerically, in the decay modes considered in this paper, the CKM-favored
$B_{c} \to \rho^{-}\omega, K^{*-}K^{*0} $ decays have the relatively large
branching fractions, $\sim {\cal{O}}(10^{-7})$, and hence are likely to be the
first observed by the future experiments. In addition, all of the decay modes
are dominated by the longitudinal polarization state; numerically, $f_{L}(B_{c}
\to VV) \gtrsim 99\%$.
