  We report on extensive molecular dynamics atomistic simulations of a
\textit{meta}-substituted \textit{poly}-phenylacetylene (pPA) foldamer
dispersed in three solvents, water \ce{H2O}, cyclohexane \ce{cC6H12}, and
\textit{n}-hexane \ce{nC6H14}, and for three oligomer lengths \textit{12mer},
\textit{16mer} and \textit{20mer}. At room temperature, we find a tendency of
the pPA foldamer to collapse into a helical structure in all three solvents but
with rather different stability character, stable in water, marginally stable
in n-hexane, unstable in cyclohexane. In the case of water, the initial and
final number of hydrogen bonds of the foldamer with water molecules is found to
be unchanged, with no formation of intrachain hydrogen bonding, thus indicating
that hydrogen bonding plays no role in the folding process. In all three
solvents, the folding is found to be mainly driven by electrostatics, nearly
identical in the three cases, and largely dominant compared to van der Waals
interactions that are different in the three cases.
  This scenario is also supported by the analysis of distribution of the bond
and dihedral angles and by a direct calculation of the solvation and transfer
free energies via thermodynamic integration. The different stability in the
case of cyclohexane and n-hexane notwithstanding their rather similar chemical
composition can be traced back to the different entropy-enthalpy compensation
that is found similar for water and n-hexane, and very different for
cyclohexane.
  A comparison with the same properties for \textit{poly}-phenylalanine
oligomers underscores the crucial differences between pPA and peptides.
  To highlight how these findings can hardly be interpreted in terms of a
simple "good" and "poor" solvent picture, a molecular dynamics study of a
bead-spring polymer chain in a Lennard-Jones fluid is also included.
