[anderson]

Not sure if I'm posting in the correct board, but here goes:

I'm trying to figure out what the "K" values for polyvinylpyrrolidone (povidone) refer to.  I thought K values generally were related to acid/base relationships.  However, with povidone I've seen some references to viscosity, which doesn't make any sense to me.  When I google it I just get a number of commercial sites with prices for povidone K15, povidone K30, povidone K90, etc.

Specifically I'm trying to figure out the relationship between K value and binding strength between povidone and iodine.  My initial search seems to indicate that a lower K value translates to a lower binding strength with iodine, but I'm just not sure.

Anyone know what the K value is referring to?  Anyone know if a lower or higher K value povidone would have weaker or stronger iodine binding? 

Main bottom line question:  If I had a K15 povidone-iodine solution and a K90 povidone-iodine solution (same concentrations, temps, pH, etc), which solution would have the higher ratio of free to bound iodine?

Thanks in advance for your help (this isn't for a test or homework!)

[polymergirl]

The "K" value that the manufacturers are referring to indicates the molecular weight ie 30K PVP has a molecular weight of around 30,000 Da.

[Sacauntos]

the valor of the molecular weight in polimers allows to know the size of the polimer chain. In the case of PVP a bigger chain has more ratio of free to bound.

[Dangerous Liaison]

Just FYI, you are seeing k value associated with viscosity because a standard method for determining povidone k-value uses a capillary viscometer.  Using the solution concentration and the determined viscosity relative to water, you perform a horrendous calculation and voila!  K-value.

If anyone out there can tell me more about this calculation and how it was derived, I am all ears.

JR, Compendial Liaison

[gluedudeguru]

The "K" value that the manufacturers are referring to indicates the molecular weight ie 30K PVP has a molecular weight of around 30,000 Da.

I was so sure that i was going to agree with you, until i went looking out on the world wide web, deep.

"
*1 Fikentscher’s value of viscosity characteristics K-value represents a viscosity index relating to molecular weight and is calculated by the following Fikentscher’s formula with relative viscosity which is measured by capillary viscometer at 25ºC 
K= (1.5 logηrel -1)/ (0.15+0.003c)+ (300c logηrel + (c+1.5clogηrel )2)1/2/ (0.15c+0.003c2)
ηrel : Relative viscosity of aqueous polyvinylpyrrolidone solution to water
c : Content (w/w%)of polyvinylpyrrolidone in aqueous polyvinylpyrrolidone solution
"

I dont know 100% what they are trying to say but at least it is a FUNCTION of MW.

http://www.shokubai.co.jp/eng/products/pvp.html