  We studied structures formed by a single $(AB)_k$ multiblock copolymer chain,
in which interaction between A-type beads was purely repulsive, and B-type
beads tended to aggregate. We studied how attraction between A-type beads and
B-type beads affected the structure of the chain. We discovered formation of an
equilibrium globular structure, which had unique heterogeneous
checkerboard-like distribution of contact density. Unlike the structures
usually formed by a single $(AB)_k$ multiblock copolymer chain, this structure
had contact enrichment at the boundaries of A and B blocks. This structure was
formed by a multiblock copolymer chain, in which B-type beads could form
maximum two reversible bonds either with A-type or B-type beads, A-type beads
could form maximum one reversible bond with a B-type bead, and interactions
between A-type beads were purely repulsive. Multiblock copolymer chains with
this type of intrachain interactions can model structure of chromatin in
various organisms.
