How to calculate soft and hard segment percentage in polyurethanes? Means in a polyurethane we are using polyol, diisocyanate and chain extender then we get polyurethane polymer. So I want to know what is the percentage of hard segment in that PU? How we calculate that what is the formula?
When you have a junction such as Polyol-Diisocyanate-Polyol, then the Diisocyanate is actually not part of the hard segment (it will be in the soft phase). So the % of (Iso+chain extender) is actually greater than the % of hard segment. To accurately answer this requires relative reactivity of the chain extender vs. polyol. I have been able to work out the solution in the case of polyurethane foams (i.e. water & polyether polyol, reacted with TDI). Please see the attached link to the following paper.
http://www.sciencedirect.com/science/article/pii/S0032386113006381
The iscyanate + chain extender is the hard segment, he polyol is the soft segment. It can be used if you prepare the PUR yourself. In the case of a commercial sample it can be estimated by various analytical methods, but it is not easy at all.
When you have a junction such as Polyol-Diisocyanate-Polyol, then the Diisocyanate is actually not part of the hard segment (it will be in the soft phase). So the % of (Iso+chain extender) is actually greater than the % of hard segment. To accurately answer this requires relative reactivity of the chain extender vs. polyol. I have been able to work out the solution in the case of polyurethane foams (i.e. water & polyether polyol, reacted with TDI). Please see the attached link to the following paper.
http://www.sciencedirect.com/science/article/pii/S0032386113006381
If the sample is soluble, I think NMR is the best technique. If there is an overlapping of signals in 1H you should use 13C-NMR under quantitative conditions.
You can also try thermal methods like DSC and TGA. Different hard to soft segment ratios cause differences in thermal behaviors and crystalline structures of the synthe-
sized PU.
The classical way to quantify hard and soft segments in PU is X-ray diffraction (see for instance: Szycher´s Handbook of Polyurethanes). PU properties are not only determined by the percentage of hard and soft seqments, but also the tertiary structure in form of domaines of ordered hard and soft segments.
Is it possible to calculate the soft and hard segment of TPU by FTIR?
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