Friday, November 16, 2012

Water-soluble inherent viscosity... more data coming soon

Over-time Polyscitech has developed several polymers including many which are water soluble but not soluble in organic solvents.  As our current GPC analysis system requires the use of organic solvents there has been difficulty in ascertaining the MW values of these polymers.
In order to obtain a relative estimate of MW of non-dichloromethane PST polymers the inherent viscosity of these in cold water was obtained by rheometric methods.
To do this solutions of each polymer were dissolved in deionized water as 2% w/v. A series of PEG standards (Fluka GPC standard) were used as a calibration-comparison. Each solution (2ml) was pipetted into the gap between a 60mm 2degree cone and a plate held at 5oC on a peltier temperature controlled Rheometer (TA rheometer AR550).  Each sample initially conditioned at 5C for 30seconds and pre-sheared at 1s-1 for 10 seconds to ensure correct temperature and mixing.  Each sample tested 3 times with a continuous ramp of a shear rate ranging from 10 to 0.03s-1 over the course of 2 minutes with sampling every 2 seconds
The collected data points were analyzed using Rheology Advantage Data Analysis software using the Newtonian model to obtain solution viscosity (slope) which was averaged for the three runs.  This viscosity was subsequently divided by the reported viscosity of pure water at 5C (1.519x10-3) and the natural log of this was taken.  This was then divided by solution concentration of 2g/dL to obtain the inherent viscosity of each solution.
The series of PEG standards tested displayed a logarithmic relationship between MW and inherent viscosity which is typical.  This relationship is shown in the image.  Note that this will be updated as more data becomes available but this gives an initial estimate.  Note that although the Mark-Houwink values for PEG and the various water-soluble polymers generated are not the same they should be fairly similar and as such this is a reasonable way to estimate relative MW of these polymers by inherent viscosity. 
Polyvivo AO19 B#0 was also tested by this same method and the inherent viscosity was determined to be 0.54 (g/dL) which would yield an estimated MW of ~56,000Da.  As time goes on this method will be further developed so as to ascertain MW values for this and other polymers.
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