Development of characterization techniques for polyurethanes I. Characterization of SRM 1480, a low molecular weight polyurethane for SEC calibration

Abstract

The characterization of a pol 3 rurethane standard reference material, SRM 1480, is described. The weight-average molecular weight of SRM 1480 by light scattering was determined to be 4.7 x lO'* g rnole"^. The intrinsic viscosity of SRM 1480 in THF was also measured and found to be 43.8 mL/g. The Size Exclusion Chromatography (SEC) of SRM 1480 in THF as received in the bottle was found to exhibit concentration dependent peak positions, even at low concentrations. The addition of 0.01 moles per liter LiBr to the THF was found to alleviate this problem. This low concentration of LiBr did not change the Polystyrene calibration of the SEC columns.

Determination of the weight average molecular weight of SRM 1480

“…Additional studies on the degradation of SRM 1480 in DMAC were made by running the SEC after storing the solution for a known time. These studies, which are described in a previous report [ 1 ], showed a shift in the SEC peak only after the solutions were stored in the dark for more than a week.…”

“…The effect of column loading and the addition of controlled amounts of water were studied to see their effect on this problem. None of these were effective in improving the shape or repeatability of the peak position as a function of concentration [1].…”

“…The method of homogenization and bottling was described in an earlier report [1]. 324 samples were bottled.…”

“…On the basis of these results we estimated the limiting viscosity number of SRM 1480 to be 43.8 mL/g with a standard deviation of 0.17 mL/g. Table 1 and figure 2 give the data used in the fit [1].…”

“…In eqn (1) Iq is the scattering signal from the benzene working standard at $= 90°. In order to use eqn (1) for the estimation of molecular parameters, we must first decide how many terms on the right-hand side must be included to provide an adequate fit to the experimental data.…”