  We have studied the thermodynamics of isolated homopolymer chains of varying
stiffness using a lattice model. A complex phase behaviour is found; phases
include chain-folded `crystalline' structures, the disordered globule and the
coil. It is found, in agreement with recent theoretical calculations, that the
temperature at which the solid-globule transition occurs increases with chain
stiffness, whilst the $\theta$-point has only a weak dependence on stiffness.
Therefore, for sufficiently stiff chains there is no globular phase and the
polymer passes directly from the solid to the coil. This effect is analogous to
the disappearance of the liquid phase observed for simple atomic systems as the
range of the potential is decreased.
