A Model for High Temperature Coil Globule Transitions in Compressible Solvent

A quantitative mean-field model for thermally induced (upon heating) polymer coil-to-globule transition (LCGT) is developed with no adjustable parameters. This model also yields correct qualitative trends for the more familiar thermally induced globule-to-coil transition (UCGT). Calculated LCGT temperatures show good agreement with experimental LCSTs. The physics of the UCGT and LCGT transitions are shown to be consistent with the physics of the UCST and LCST transition, respectively. Both the low and high temperature globular states are characterized by the dominance of attractive polymer self interactions over excluded volume interactions. A qualitative phase diagram containing an UCGT and a LCGT is developed for a single chain. The form of the single chain phase diagram supports the idea that, at the same temperature, the average monomer density in an isolated chain equals the global monomer density in the semi-dilute polymer phase. This model can be easily generalized to treat cross-linked gels and their contraction-expansion characteristics. An extension of this model to include electrostatic interactions will address the behavior of smart synthetic polymers used in biomedical applications as well as the phenomenon of cold denaturation of proteins