The most common technology used for Liquefaction of MDI is to introduce Carbamate or carbonized diimine groups into 4,4'-MDI, thus liquid MDI modifier was obtained. In addition to this, during the production of MDI, increase 2,4'-MDI content which results in MDI being liquefied(Or mixed TDI into MDI to form mixed diisocyanate with low freezing point). The principle of each method is to change the crystallization of the product by introducing compatible impurities. The crystallization was eliminated at room temperature. Of course, the NCO content of the product has decreased. But it doesn't change the functionality of the product, it's still going to be 2.

Characteristic:

The Characteristic of the products obtained by different manufacturers and modification methods are different. Take Huntsman 9259 for example:

Product Grade:
Carbonized diimide - urea ketinimine modified MDI. MDI-100HL is a liquefied MDI containing high efficiency catalyst, MDI-100LL is a liquefied MDI containing low efficiency catalyst, mainly used for microporous polyurethane sole, whole leather foam and coating. MDI-50HL is a liquid MDI with high efficiency catalyst and high 2,4 '-volume content, MDI-50LL is a liquid MDI with low efficiency catalyst and high 2,4' -volume content. The four types of carbonized diimine modification of liquefied MDI NCO mass fraction is 28% ~ 30%, appearance is light yellow liquid, and viscosity are no greater than 60 mPa s., freezing point is 15 ℃, density (25 ℃) in 1.21 ~ 1.23 g/cm3, acid points (in HCl mass fraction) is 0.04%. Average functionality is slightly over 2.0. MDI-100LL is more stable than MDI-100HL in storage, and MDI-100HL has slightly darker color.
Polyols modified MDI. Also known as modified polymerized MDI, it is a mixture of polyalcohol modified diphenylmethane diisocyanate and polyphenylpolymethylene isocyanate. It is a brown liquid at room temperature and can be used to prepare polyurethane high-resilience foam, polyurethane self-skin foam or other RIM products.

Usage:
MDI can be liquefied to obtain convenient and stable liquid MDI. With MDI as the basic component, this product can be used for the manufacture of high-performance microporous polyurethane elastomers, moulded soft polyurethane and self-skin foam plastics, including soles, solid tires, as well as automobile bumpers, fenders, shock absorbers, flow baffles, steering wheel, seat headrest, armrest, interior decoration and so on. It is also widely used in the manufacture of adhesives, coatings, fabric coating finishing agents, etc. It is mainly used for the manufacture of cold curing and high resilience PU soft foam, self-skinning soft foam and semi-hard foam products. Such as car, train seat cushion, steering wheel and handrail and so on product manufacture.
Mix well before use. Partial crystallization might occur due to low temperature or prolonged exposure, it can be melted under the temperature of 60-70 ℃, stir well before use.