Hi all. Is there any crosslinking retarder for polyurea/polyurethane polymer? Thanks in advance
I do not fully understand your question. By selecting the proper catalyst and temperature you can adjust the overall reaction rate. Crosslinking sometimes occurs spontaneously via side reactions - in this case it will go more or less parallel with the main reaction. Most frequently corsslinking occurs due to the fact that the functionality of the isocyanate componets (and less frequently that of the polyol or the amine crosslinker in polyureas) exceeds 2. In this case again crosslinking will proceed simultaneously with the main reaction. You can specifically retard crosslinking (which in an arbitrary selection) if you have isocyanate and polyol with a functionality of exactly 2 or lower and if you use a specific crosslinker (which can be a multivalent isocyanate, polyoel or chain extender) with a reactivity different form the main components. In this case you can regulate specifically the crosslinking rate. Another option is to prepare a strictly liner polyurethane containing unsturation and perform the crosslinking by a different mechanism (e.g. free radical polymerization). This occurs e.g. in PUR-polyester hybrids or PUR- vinylester hybrids.
MTBHQ is an effective polymerization inhibitor for use in storing and shipping unsaturated polyesters and certain other polymerizable systems. Be very careful though, its potency diminishes with increasing temperature. MTBHQ is an effective retarder even at temperatures as high as 114°C.
Florstab UVs are another type of retarders used mostly as in-can stabilization of unsaturated polymers and they are compatible with a wide range of commercially available oligomers. Mostly recommended for use in epoxy, polyester or urethane acrylate systems.
thanks for the suggestion and explanation. Actually I am looking forward to chemical substance that can delay gelation time of polyurethane/polyurea at 80 degree celcius since the reaction is too fast at the temperature mentioned
There are only catalysts for the NCO-OH or NCO-amine reaction in which the latter is fast enough without catalysts, in many cases to fast. But there are no inhibitors for these reactions. There is no chemical way to slow down the isocyanate-nucleophile reaction with given reactants. You can only change the reactants, e.g. more steric hinderance. A physical way is to decrease the temperature.
- Badges
- Science topic