The repeated sequence in this polymer is a common feature of elastin, a fibrous network protein that occurs in mammalian artery walls. Decreased entropy due to the higher degree of conformational order is compensated by the disordering of previously constrained solvent molecules, and by the increased freedom of ordered macromolecular segments to undergo small rotations and translations.Ĭross-linked (Val-Pro-Gly-Val-Gly) n (n ≈ 100) is a good example of a polymer network that exhibits an inverse temperature transition in an aqueous environment. Some polymers can even undergo a disordered-to-helix conformational transition. As temperature rises, polymer-polymer contacts become increasingly favourable compared to polymer-environment contacts, so the backbone conformation becomes more restricted.
#HYDROPHOBIC EFFECT ENTROPY FREE#
Initially, the polymer is hydrated because, even though the polymer-water contacts are slightly unfavourable, the separated chains acquire greater free volume and conformational mobility. The polymer must be slightly hydrophobic, must have a flexible backbone, and must be free to exploit this flexibility and undergo conformational changes. It is not necessary for the polymer to be in solution the inverse temperature transition can occur just as readily in a crosslinked polymer network in an aqueous environment ( Urry 1988). These transitions are a consequence of the hydrophobic effect in some polymer/water systems. Emily Renuart, Christopher Viney, in Pergamon Materials Series, 2000 8.3.3.3 Inverse temperature transitions ( Urry et al.
0 kommentar(er)
