The possibility of an accurate determination of polymer molecular weight and polydispersity by thermal field-flow fractionation (ThFFF) retention measurements is' here discussed with reference to the use of only physicochemical data of ordinary and thermal diffusivity, but without need of prior calibration of the ThFFF system. Special emphasis is devoted to the check of linearity conditions of retention data determination, i.e., on the proper sample loading and thermal field strength to be chosen for unbiased polymer specifications determination. Different numerical methods of determining peak profile attributes (non¬linear peak fitting procedures by Edgeworth-Cramer series expansions, numerical integration, graphical determination) are compared. The approach is applied to a standard polystyrene sample, with ethylbenzene as polymer solvent and carrier liquid, as extensive physicochemical informations on this polymer-solvent system are available in the literature. In addition, it is shown that the combination of retention and plate height measurements provides an absolute and accurate method of determination of the thermal diffusion coefficient of the sample.
EVALUATION OF A STANDARDLESS METHOD OF DETERMINATION OF MOLECULAR WEIGHT AND POL YDISPERSITY OF A POLYSTYRENE SAMPLE BY THERMAL FIELD-FLOW FRACTIONATION
CONTADO, Catia;DONDI, Francesco
1997
Abstract
The possibility of an accurate determination of polymer molecular weight and polydispersity by thermal field-flow fractionation (ThFFF) retention measurements is' here discussed with reference to the use of only physicochemical data of ordinary and thermal diffusivity, but without need of prior calibration of the ThFFF system. Special emphasis is devoted to the check of linearity conditions of retention data determination, i.e., on the proper sample loading and thermal field strength to be chosen for unbiased polymer specifications determination. Different numerical methods of determining peak profile attributes (non¬linear peak fitting procedures by Edgeworth-Cramer series expansions, numerical integration, graphical determination) are compared. The approach is applied to a standard polystyrene sample, with ethylbenzene as polymer solvent and carrier liquid, as extensive physicochemical informations on this polymer-solvent system are available in the literature. In addition, it is shown that the combination of retention and plate height measurements provides an absolute and accurate method of determination of the thermal diffusion coefficient of the sample.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
