Scleroglucan gel volume changes in dimethylsulphoxide/water and alkaline solutions are partly caused by polymer chain conformational transitions

The relative equilibrium volume, V/V-0, of swollen scleroglucan gels was de termined at temperatures T from 4 to 40 degrees C in aqueous alkaline solut ions and binary solvents containing water and dimethylsulphoxide (DMSO), re spectively. In some of the experiments scleroglucan was crosslinked using s odium-meta-periodate. In others the crosslinks were Schiff bases between th e polyaldehyde of scleroglucan and primary amines on small amounts of added chitosan. The V/V-0 showed discontinuous changes at a water weight fractio n W-H = 0.13, independent of the temperature from 4 to 40 degrees C in DMSO /water solvents. The V/V-0 of the gels decreased when the pH in aqueous sol vents was raised above 13. Both these findings coincide with the known stra nd separation of the triple-helical structure occurring under these solvent conditions. An additional abrupt change in V/V-0 occurred at W-H = 0.84 an d T = 20 degrees C for the binary DMSO/water solvents. This transition was shifted towards lower W-H for increasing temperatures, at T = 40 degrees C it occurred at W-H = 0.56, which is similar to the temperature effect of th e intra-triple-helical conformational transition of scleroglucan. This stud y indicates that the conformational transitions of the elastically active c hains of the polymer network can affect the equilibrium volume of swollen p olymer gels. (C) 1999 Elsevier Science Ltd. All rights reserved.