  We present a generalized theory for studying static monomer density-density
correlation function (structure factor) in concentrated solutions and melts of
dipolar as well as ionic polymers. The theory captures effects of electrostatic
fluctuations on the structure factor and provides insights into the origin of
experimentally observed enhanced scattering at ultralow wavevectors in
salt-free ionic polymers. It is shown that the enhanced scattering can
originate from a coupling between fluctuations of electric polarization and
monomer density. Local and non-local effects of the polarization resulting from
finite sized permanent dipoles and ion-pairs in dipolar and charge regulating
ionic polymers, respectively, are considered. Theoretical calculations reveal
that, similar to the salt-free ionic polymers, the structure factor for dipolar
polymers can also exhibit a peak at a finite wavevector and enhanced scattering
at ultralow wavevectors. Although consideration of dipolar interactions leads
to attractive interactions between monomers, the enhanced scattering at
ultralow wavevectors is predicted solely on the basis of the electrostatics of
weakly inhomoge- neous dipolar and ionic polymers without considering the
effects of any aggregates or phase separation. Thus, we conclude that neither
aggregation nor phase separation is necessary for observing the enhanced
scattering at ultralow wave-vectors in salt-free dipolar and ionic polymers.
For charge regulating ionic polymers, it is shown that electrostatic
interactions between charged monomers get screened with a screening length,
which depends not only on the concentration of free counterions and coions but
also on the concentration of adsorbed ions on the polymer chains. Qualitative
comparisons with the experimental scattering curves for ionic and dipolar
polymer melts are presented using the theory developed in this work.
