Title: LOW-VISCOSITY REACTIVE POLYURETHANE COMPOUNDS

 Number/Link: WO2013092564 (in German)

Applicant/Assignee: Bayer

Publication date: 27-06-2013

“Gist”: A prepolymer with very low free diisocyanate content and relatively low viscosity can be prepared by reacting MDI having a high 2,4′ isomer content with a low MW diol in a first step and adding a high MW polyol in a second step.

Why it is interesting: The use of asymmetric diisocyanates (having isocyanate groups with different reactivities) to prepare prepolymers with low free monomers is well known.  Prepolymers prepared using diisocyanates with high levels of 2,4′-MDI, 2,4-TDI, IPDI etc. will however still show a very high viscosity at low isocyanate content. Bayer has now found that prepolymers with lower free monomer and lower viscosity can be prepared by using two polyols reacted in seperate stages. In a first step an MDI with >95% 2,4′ isomer is reacted with a (pref) diol with a molecular weight between 60 and 700 to produce a prepolymer with an NCO content of more than 15%. In a second step this prepolymer is then further reacted with a ‘conventional’polyol to obtain the final prepolymer.  In an example a prepolymer with less than 0.1% free MDI and a viscosity of 25 Pa.s at 40°C was prepared.

2,4′-MDI