electronic and conformational properties of a single polyacetylene chain in solution has been studied as a function of temperature. Monte Carlo simulations, using the Su-Schrieffer-Heeger Hamiltonian, show that bond-length variations, and rotations about the bonds both give important, but opposing, contributions to the temperature dependent band gap. For the case of polyacetylene, the net effect is shown to be an increase of the band gap with temperature, similar to experimental findings on other conjugated polymers. The electronic structure is coupled to the global conformation via the conjugation length. Temperature induced off-diagonal disorder is also found to produce tails in the density of states that reaches into the band gap of the ground state polymer, which could be of experimental significance.