Accuracy of Polymer Structure Determination

Abstract

Three independent determinations have been made of the crystalline structure of the α-phase of poly (tetramethylene terephthalate). The data on which these determinations have been based are used to asses the contributions to the uncertainties of the structural parameters caused by errors in the unit cell parameters, structure factors, and bond parameters. The effects of differences in the model from which refinement is started are also assessed. The major contribution to uncertainty arises from errors in the structure factors (the "R-factor" between structure factor sets from two different laboratories can be greater than 20%) but errors in bond parameters also make a sizeable contribution. Hamilton's test indicates that one of the structure factor sets used in this study is less inaccurate than the other two and using this the best model satisfying all the other data is estimated together with the uncertainties in its parameters.