Are polymer melts “ideal”?

It is commonly accepted that in concentrated solutions or melts high-molecular weight polymers display random-walk conformational properties without long-range correlations between subsequent bonds. This absence of memory means, for instance, that the bond–bond correlation function, P(s)P(s), of two bonds separated by s monomers along the chain should exponentially decay with s  . Presenting numerical results and theoretical arguments for both monodisperse chains and self-assembled (essentially Flory size-distributed) equilibrium polymers we demonstrate that some long-range correlations remain due to self-interactions of the chains caused by the chain connectivity and the incompressibility of the melt. Suggesting a profound analogy with the well-known long-range velocity correlations in liquids we find, for instance, P(s)P(s) to decay algebraically as s−3/2s−3/2. Our study suggests a precise method for obtaining the statistical segment length bebe in a computer experiment.