While reading papers on polyurethane synthesis, a question arose.
Q1.
MDI [methylene di(p-phenyl) isocyanate] 2mmol
PTMO[poly(tetramethylene oxide)] 1mmol
1,4-butanediol 0.9mmol
dodecyltrimethylammonium (DTA)-hyaluronic acid (HA) 0.04mmol
Since DTA-HA has 4 -OH groups excluding the bonded carboxyl group, shouldn't only 0.025 mmol of DTA-HA be added in theoretically?
ps. HA (4.7 kDa sodium salt; Lifecore Biomedical, Inc., Chaska, MN) was used and preparad for DMF-Soluble HA Salts
Q2.
In table 1 (attached photo), the molar ratio of "di-ol/amine + extender" is much higher than that of isocyanate. Is this chemically possible?
Q1
When you have theoretical NCO/OH ratio = 1 in linear polymer case it means that theoretical molecular weight could potentially go to infinity. In reality it does not happen, because reaction rate drops due to dramatically low concentration of free reactive groups and chain mobility of polymer. Lets just say, that NCO and OH groups can not meet each other and react.
If you need polymer with certain end groups usually component containing these groups goes in excess.
However, in a system with polyfunctional components (such as DTA-HA), NCO/OH ratio going toward 1 increase probability of gel formation. Using only 0,025 mol in theory would mean that all 4 groups of DTA-HA have reacted producing branched unit -> crosslinked structure = gel. In order to avoid that certain component goes in access and terminates chain grow.
Q2
If you want a polymer with certain end groups (as it is mentioned in an article you provided) and limited molecular weight component containing necessary groups goes in excess.
Igors Sivacovs
I finally understand your answer. In reality, as I add the materials to make polyurethane, the reaction rate decreases, so I need to supply the last material much more than the theoretical amount to fully combine it in polyurethane, right?
And the reason why R ratio of Product is under 1 [IPDI(-NCO):BATPBP+MDEA(-OH)
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