Abstract
We consider the theory obtained by adding to the usual
string frame dilaton gravity action specially constructed higher
derivative terms motivated by the limited curvature construction
of [1]
and determine the spatially homogeneous and isotropic solutions to the
resulting equations of motion. All solutions of the resulting theory
of gravity with these symmetries are nonsingular and all curvature
invariants are bounded. For initial conditions inspired by the
pre-big-bang scenario solutions exist which correspond to a spatially
flat Universe starting in a dilaton-dominated superinflationary phase
with 
> 0 and having a smooth transition to an expanding
Friedmann Universe with < 0. Hence, the graceful exit
problem of pre-big-bang cosmology is solved in a natural way.