Abstract
A problem of the configurational properties of a long flexible polymer chain with a quenched disorder is considered. The chain is assumed to be randomly constructed from monomers of two different kinds with different constants for the two-body interaction. Near the theta point, i.e. when the average interaction of monomers is small, the spatial correlation of the repulsive and attractive monomers of different kinds leads to an increase of effects of the disorder on large scales. There is also the competing effect of the repulsive three-body interaction which tends to screen the effects of disorder on large scales. For both effects the upper critical dimension is dc=3. A solution of the renormalisation group equation indicates that there always exists a critical scale at which the relative dispersion of sizes of polymers with different random sequences of monomers becomes of the order of unity. The magnitude of this critical scale depends strongly on the relation between the constant which characterises the dispersion of the two-body interaction B0 and the constant of the repulsive three-body interaction V0. If B0<3/32V0 at each physically attainable scale the effects of screening are prevalent and the dispersion of sizes of polymers with different sequences of monomers is small near the theta point. If the reverse inequality holds, the dispersion of sizes becomes of the order of unity near the theta point.