Polynomials with palindromic and unimodal coefficients

Let f(q)=a_rq_r+···+ a_sq^s, with a_r=0 and a_s=0, be a real polynomial. It is a palindromic polynomial of darga n if r+s=n and a_r+i=a_s-i for all i. Polynomials of darga n form a linear subspace P_n(q) of R(q)_n+1 of dimension n/2]+1. We give transition matrices between two bases {q^j(1+q+··· +q^n-2j)},{q^j(1+q)^n-2j and the standard basis q^j(1+q^n-2j) of P_n(q). We present some characterizations and sufficient conditions for palindromic polynomials that can be expressed in terms of these two bases with nonnegative coefficients. We also point out the link between such polynomials and rank-generating functions of posets.