Quantum path-integral molecular-dynamics simulations of poly(propylene oxide) (PPO) have been performed at 300 K. We find excellent agreement for the short and intermediate range structural order as deduced from neutron diffraction measurements. The result from the quantum simulation agrees better with experimental data compared with the classical simulation using the same atomistic force field. It shows that in a detailed comparison with accurate experimental data the quantum effects of the atomic motion have to be taken into account. The results for the protonated and deuterated systems are compared and the corresponding static structure factors show very minor differences.