Hydrodynamic properties of some amylose esters

Abstract

This thesis is concerned with the properties of amylose esters in solution. Three esters have been studied in various solvents, the tributyrate, tripropionate and to a lesser extent the triacetate. Chapter I gives details of the various experimental methods used and their theoretical background. Measurements of the limiting viscosity number, the weight average molecular weight and the number average molecular weight have been made. No change in the viscosity was found with decreasing shear rate. Chapter II details the method s of preparation of linear amylose and the three esters. The amylose was analysed for linearity and purity by 3-amylolysis. The esters were prepared by reaction of amylose with the appropriate anhydride in pyridine. Two batches of the tripropionate and the tributyrate were prepared. Low molecular weight fractions of the triacetate and tripropionate were obtained. Difficulty was found on trying to fractionate the high molecular weight sample of the tripropionate. This sample was found to exhibit anomalous solution behaviour in subsequent measurements. The degree of substitution was checked by Infra-red spectroscopy. In Chapter III the results are recorded for each ester. Measurements of A^ by osmometry are discussed in the light of theories concerning its dependence on molecular weight. Theories relating the expansion coefficient to the molecular weight are also discussed. Various theories have been used to estimate the unperturbed dimensions from viscosity measurements in good solvents. The methods due to Stockmayer and Fixman, Kurata and Stockmayei;, Flory and Fox, Ptitsyn, Berry, Bohdanecky and Inagaki, Suzuki and Kurata were used. The unperturbed dimensions of amylose tributyrate were found to vary with solvent and values of (r- 20/M-w) ½ varied from 523 x 10-11 cm to 576 x 10-11 cm (Φ0 equals 2.87 x 1023). The temperature dependence of the unperturbed dimensions of amylose tributyrate shows a minimum at about 308K and a tentative explanation of change in ring conformation has been put forward. The unperturbed dimensions of the tripropionate and triacetate were not found to be solvent dependent and had values for (r- 20/M-w) ½ of 575 x 10-11 cm and 559 x 10- -11 cm , respectively. Both esters exhibit a negative temperature dependence of viscosity and unperturbed dimensions. The flexibility of the esters, in terms of parameters such as the Kuhn statistical segment and the Kirkwood-Riseman effective bond length, was found to decrease as the side chain lengthened. The esters were compared with the cellulosic polymers and found to be much less extended and more flexible in solution. The esters were also compared with synthetic polymers and found to be less flexible.