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Coils, globules and single chain glasses
Author(s) -
Napper Donald H.
Publication year - 1995
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.19950980180
Subject(s) - endothermic process , polystyrene , materials science , exothermic reaction , chemical physics , swelling , crystallography , hysteresis , polymer , polymer chemistry , thermodynamics , chemistry , adsorption , condensed matter physics , composite material , organic chemistry , physics
The cyclic coil‐globule‐coil transitions for poly(N‐isopropylacrylamide) tethered to an interface exhibit unexpected phenomena. Two, not the predicted single, coil‐to‐globule transitions can be observed: the one that is predicted occurs in worse than θ‐solvents whereas the other is observed in better than θ‐solvents. The latter phenomenon appears to be associated with the the formation of n‐clusters, first postulated by de Gennes. The chains in their globular form were found to undergo an entropy driven entanglement process that prevents reversible swelling in the globule‐to‐coil transition and leads to hysteresis in the layer thickness. Single chain glasses of polystyrene prepared by microemulsion polymerisation display physical properties different from those of multichain glasses including a higher conformational temperature, larger free volume and a predominantly exothermic rather than an endothermic DSC scan near T g . These observations have been attributed to the occurrence of cohesional entanglements.