Polymeric MDI (crude MDI) is specifically enumerated under 390931 as a distinct amino-resin subheading, separate from polyurethanes at 390950. The key distinction is chemical identity: polymeric MDI is a mixture of methylene diphenyl diisocyanate isomers and oligomers, not yet reacted into a polyurethane. Importers should confirm the product's CAS number and technical data sheet to support the correct subheading.

No — urea resins and thiourea resins have their own subheading (390910), while melamine resins are separately enumerated under 390920. Both are amino-resins within heading 3909, but the chemical distinction between urea-based and melamine-based systems is the classification criterion.