  We use computer simulations to investigate how a catalytic reaction in a
polymer sol can induce the formation of a polymer gel. To this aim we consider
a solution of homopolymers in which freely-diffusing catalysts convert the
originally repulsive A monomers into attractive B ones. We find that at low
temperatures this reaction transforms the polymer solution into a physical gel
that has a remarkably regular mesostructure in the form of a cluster phase,
absent in the usual homopolymer gels obtained by a quench in temperature. We
investigate how this microstructuring depends on catalyst concentration,
temperature, and polymer density and show that the dynamics for its formation
can be understood in a semi-quantitative manner using the interaction
potentials between the particles as input. The structuring of the copolymers
and the AB sequences resulting from the reactions can be discussed in the
context of the phase behaviour of correlated random copolymers. The location of
the spinodal line as found in our simulations is consistent with analytical
predictions. Finally, we show that the observed structuring depends not only on
the chemical distribution of the A and B monomers but also on the mode of
formation of this distribution.
