  The phase structure of a homopolymer chain is investigated in terms of a
universal theoretical model, designed to describe the infrared limit of slow
spatial variations. The effects of chirality are studied and compared with the
influence of a short-range attractive interaction between monomers, at various
ambient temperature values. In the high temperature limit the homopolymer chain
is in the self-avoiding random walk phase. But at low temperatures, two
different phases are possible: When short-range attractive interactions
dominate over chirality, the chain collapses into a space- filling
conformation. But when the attractive interactions become weaker, there is a
low temperature unfolding transition and the chain becomes like a straight rod.
Between the high temperature and low temperature limits, several intermediate
states are observed. For sufficiently high values of short-range attraction,
the conventional {\theta}-regime is observed between the self-avoiding random
walk phase and the space filling collapsed phase. But when chirality increases,
there is a trasition from the {\theta}-regime to a pseudogap state. Moreover, a
regime akin the {\theta}-regime is identified between the pseudogap state, and
the low temperature phase where the chain is like a straight rod. Applications
to polymers and proteins, in particular collagen, are suggested.
