# OH Index

How does one calculate the 'OH index' of polyols for use in PU
synthesis - or is this a value that is experimentally determined. Is
it the number of moles of OH contained within a Kg of polyol - I am
comfortable using normal stoichiometric calculations but would like to
get to grips with this type of PU industry nomenclature.
Kind regards,
Gillian
It's normally quoted as the "OH number". This is expressed as the number of milligrammes of KOH per kg of resin that would contain the equivalent number of OH groups (strange I know). So, if you have a diol of 1000 molecular weight, the OH value would be 56100 (molar weight of KOH expressed in mg) x 2 (functionality) / 1000 (molecular weight of diol) = 112.2. Actually 1000MW diols are usually quoted as OH value 110, or a range from 107 - 113 or something similar.
Kind regards
Colin
Dr Colin D Reed Business Development Manager Rosehill Polymers Ltd

Colin - thanks a million for your answer - this helps a lot.
Gillian
Colin's reply refers to OH number, not OH index. In the context of viscoelastic foams, which are often made using a stoechiometric excess of OH groups, the excess can be quantified using "OH index" by analogy to yhe more widely used "NCO index". NCO index = 100* (nb of NCO equivalents)/(nb of OH + water equivalents) OH index = 100* (nb of OH + water equivalents)/(nb of NCO equivalents) where nb of equivalents = nb of moles of NCO or OH groups or 2* nb of moles of water in a given amount of (mixed but not reacted) polymer liquids used to make the foam. This should normally be explained in patents which refer to this parameter. "GillianH" a écrit dans le message de news: snipped-for-privacy@g49g2000cwa.googlegroups.com...
Hm, but this can not be applied to pure polyols, which the OP was refering to.
Regards, Oliver
OK, in the context of polyols alone, the term OH index, is indeed as explained by Colin. But "OH number" is also a frequent alternative, I believe. I thought from GillianH's previous post that he was interested in viscoelastic PU foams, where OH index is used with another meaning.
"Oliver 'Ojo' Bedford" a écrit dans le message de news:dok36o\$ibq\$ snipped-for-privacy@lnx107.hrz.tu-darmstadt.de...
I think I made it clear that I was defining OH number. From the OP's request I thought that she was interested in OH number and had just used the other term.
Colin

#### Site Timeline

• Hello, I have a used Vetaphone Corona plus generator for sale. I have used it...
• next in

## ⚗ Polymers

• i'm working on polybutadiene coagulation system. emulsion polymerization. our...
• previous in

## ⚗ Polymers

• We are having problems with a vinyl acrylic latex for White coating, it has a...
• last updated in

## ⚗ Polymers

• We are having problems with a vinyl acrylic latex for White coating, it has a...
• last posted in

## ⚗ Polymers

• Po weekendzie z wiertarką ... nie ma jakiegos laserowego dziurkacza do betonu?...
• site's last updated in

## Engineering Science (Polish)

• Po weekendzie z wiertarką ... nie ma jakiegos laserowego dziurkacza do betonu?...