  Multiblock copolymer chains in implicit nonselective solvents are studied by
Monte Carlo method which employs a parallel tempering algorithm. Chains
consisting of 120 $A$ and 120 $B$ monomers, arranged in three distinct
microarchitectures: $(10-10)_{12}$, $(6-6)_{20}$, and $(3-3)_{40}$, collapse to
globular states upon cooling, as expected. By varying both the reduced
temperature $T^*$ and compatibility between monomers $\omega$, numerous
intra-globular structures are obtained: diclusters (handshake, spiral, torus
with a core, etc.), triclusters, and $n$-clusters with $n>3$ (lamellar and
other), which are reminiscent of the block copolymer nanophases for spherically
confined geometries. Phase diagrams for various chains in the $(T^*,
\omega)$-space are mapped. The structure factor $S(k)$, for a selected
microarchitecture and $\omega$, is calculated. Since $S(k)$ can be measured in
scattering experiments, it can be used to relate simulation results to an
experiment. Self-assembly in those systems is interpreted in term of
competition between minimization of the interfacial area separating different
types of monomers and minimization of contacts between chain and solvent.
Finally, the relevance of this model to the protein folding is addressed.
