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HDI Allophanate Polyisocyanate (Low-Viscosity)

CAS 28182-81-2

An allophanate-modified aliphatic polyisocyanate based on hexamethylene diisocyanate (HDI), supplied at low viscosity to cut solvent demand. It serves as the hardener in two-component polyurethane coatings, where its NCO groups crosslink hydroxyl-functional acrylic and polyester resins. The aliphatic HDI backbone delivers the gloss and UV color stability that aromatic isocyanates cannot

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CAS Number
28182-81-2
Material Family
Polymers & Resins
At a Glance
Material Family
Polymers & Resins
Record Type
Polymer fluid
Primary Role
Crosslinking / Curing
Functional Roles
Applications & Use Cases
  • Hardener component in high-solids, low-VOC two-component polyurethane coatings
  • Automotive refinish and OEM clearcoats requiring gloss and UV color stability
  • Industrial-maintenance and protective topcoats with abrasion and chemical resistance
  • Wood and plastic coatings where low application viscosity is needed
Safety & Handling
Full SDS available on request

A grade-specific Safety Data Sheet (SDS) — with the complete hazard classification, handling precautions, and transport information — is supplied with every shipment and available on request. Confirm all safety and regulatory details against the SDS for your specific grade.

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Chemical Identity
CAS Number
28182-81-2
Synonyms & Trade Names
Allophanate-modified HDI polyisocyanate Low-viscosity aliphatic polyisocyanate HDI homopolymer Polyfunctional HDI hardener Comparable to Desmodur N 3900
Full Description

Allophanate chemistry trades some of the functionality of a standard HDI isocyanurate trimer for markedly lower viscosity, which lets formulators build high-solids, low-VOC 2K-PU coatings without heavy solvent loading. Crosslinked against polyol resins, it forms weatherable films with strong abrasion, chemical, and gloss retention, the reason aliphatic HDI hardeners dominate automotive refinish and industrial-maintenance topcoats. Typical NCO content and viscosity sit below those of conventional trimer grades; the practical trade-off is a slightly lower crosslink density per equivalent, balanced by far easier application at high solids. Like every isocyanate hardener it is moisture-sensitive and liberates HDI vapor when heated or sprayed, so engineering controls and respiratory protection govern its handling

Comparable to Desmodur N3900: RawSource supplies this as an independent equivalent (an offset) to Desmodur N3900 — it is a low-viscosity HDI allophanate-modified polyisocyanate. It is not genuine Desmodur N3900-branded material, and RawSource is not affiliated with, authorized by, or endorsed by Covestro.

Desmodur N3900 is a registered trademark of Covestro, used here solely for nominative comparison to identify the equivalent grade. RawSource supplies an independent equivalent product; confirm equivalence against your specification and the Certificate of Analysis.

Disclaimer. Information on this page — including properties, identifiers, hazard, transport (DOT/UN) and tariff (HS) classifications, and applications — is provided for general reference and is compiled from authoritative public sources (e.g. PubChem/ECHA, 49 CFR 172.101, the Harmonized Tariff Schedule). Values are typical and are not a guaranteed specification; the Certificate of Analysis (CoA) for the lot purchased governs. Products are sold for industrial and professional use only. Nothing here is a medical, health, or efficacy claim or advice. Always consult the current Safety Data Sheet (SDS) before handling, storage, transport or disposal, and confirm regulatory status, classification and suitability for your application and jurisdiction. Hazard, transport and tariff classifications must be verified for your specific shipment. RawSource makes no warranty, express or implied, and assumes no liability for use of this information. Trademarks. Third-party trademarks and brand names are the property of their respective owners; any reference is nominative — used only to identify a comparable product — and does not imply affiliation with, sponsorship by, or endorsement by the trademark owner.