  We embark on a systematic study of the $(k+1)$-th derivative of
$x^{k-r}H(x^r)$, where $H(x):=-x\log x-(1-x)\log(1-x)$ is the binary entropy
and $k>r\geq 1$ are integers. Our motivation is the conjectural entropy
inequality $\alpha_k H(x^k)\geq x^{k-1}H(x)$, where $0<\alpha_k<1$ is given by
a functional equation. The $k=2$ case was the key technical tool driving recent
breakthroughs on the union-closed sets conjecture. We express $
\frac{d^{k+1}}{dx^{k+1}}x^{k-r}H(x^r)$ as a rational function, an infinite
series, and a sum over generalized Stirling numbers. This allows us to reduce
the proof of the entropy inequality for real $k$ to showing that an associated
polynomial has only two real roots in the interval $(0,1)$, which also allows
us to prove the inequality for fractional exponents such as $k=3/2$. The proof
suggests a new framework for proving tight inequalities for the sum of
polynomials times the logarithms of polynomials, which converts the inequality
into a statement about the real roots of a simpler associated polynomial.
