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To echo André, it would be useful to see a definition of what you mean. The secondary polytope is generally defined for a point configuration, not for a polytope. Here are two definitions, the first from Carl Lee's article "Subdivisions and triangulations of polytopes" (Handbook of Discrete and Computational Geometry), and the second from Sven Herrmann's paper, "On the facets of the secondary polytope" (arXiv.0908.2737v3). In the first, $V$ is a set of points in $\mathbb{R}^d$, in the second, $\cal{A}$ is a multiset of points in $\mathbb{R}^d$.

So perhaps you are asking for the secondary polytope of a point set whose convex hull is a simplicial polytope? But that can't be what you mean: a convex polygon is a simplicial polytope in $\mathbb{R}^2$ (its facets are segments, 1D simplicies), and the secondary polytope of a pentagon is not simplicial: its facets are quadrilaterals and pentagons.
         PentagonAssoc http://cs.smith.edu/~orourke/MathOverflow/PentagonAssoc.png
         _{(Image from Discrete and Computational Geometry)}