Coil-globule collapse in flexible macromolecules

The transition of a solvated flexible macromolecular chain from random coil behavior in the theta-state to a globular compact form in the collapsed state has been the subject of extensive theoretical and experimental studies. Most of the coil-globule transition studies of macromolecules have concentrated on the prototypical polystyrene-cyclohexane system. However, chain contractions reported in this system have been around 75% of those in the unperturbed theta-state. This relatively small decrease in size does not satisfy the criterion for a densely packed, collapsed globule. Experimentally, the collapse from a coil to a true compact globular state has now been established for two flexible macromolecules: poly(N-isopropylacrylamide) in water and poly(methyl methacrylate) in various solvents. In this contribution, we review recent theoretical studies covering phenomenological and Langevin models as well as computer simulations. In addition, we outline recent experimental studies of the coil-globule transition of various flexible polymers, copolymers, and polyelectrolytes.