High-Purity Solvents, Polyurethane (PU) and Resin

Methylene Diphenyl Diisocyanate (MDI)

Methylene Diphenyl Diisocyanate (MDI) is a critical aromatic diisocyanate that serves as a fundamental building block in the global polyurethane (PU) industry. It exists primarily in three commercial forms: Monomeric MDI (MMDI), Polymeric MDI (PMDI), and modified MDI. The 4,4′-isomer (CAS 101-68-8) is the most commercially significant monomer, while PMDI (CAS 9016-87-9) is a complex mixture containing MDI isomers and higher-functional oligomers.

MDI is valued for its high reactivity with polyols, enabling the rapid synthesis of polymers characterized by exceptional mechanical strength and thermal stability. Compared to Toluene Diisocyanate (TDI), MDI exhibits a significantly lower vapor pressure at room temperature, which enhances industrial safety by reducing inhalation risks during handling. Its versatility allows for the production of everything from rigid, high-performance insulation foams to flexible elastomers and durable coatings. As industries pivot toward energy efficiency and lightweight materials, MDI remains indispensable in the construction, automotive, and appliance sectors.

Attributes

Key Features and Benefits

Superior Thermal Efficiency: Enables the production of closed-cell rigid foams with industry-leading R-values for superior insulation.
High Reactivity: Facilitates rapid curing and short cycle times in high-volume manufacturing environments, maximizing throughput.
Enhanced Occupational Safety: Lower volatility and vapor pressure compared to other diisocyanates reduce the risk of respiratory exposure during ambient processing.
Exceptional Mechanical Durability: Provides finished products with high tensile strength, abrasion resistance, and long-term structural integrity.
Tailorable Functionality: The availability of various grades (monomeric vs. polymeric) allows formulators to precisely control cross-linking density and polymer flexibility.
Excellent Adhesion: Naturally bonds to a wide array of substrates, including metals, wood, and diverse plastics, without the need for extensive primers.

Specifications

Technical Highlights

NCO Content: Typically ranges from 30.0% to 33.5% depending on the grade, dictating the stoichiometric ratio required for polyol reaction.
Average Functionality: Ranges from 2.0 for pure MMDI to approximately 2.7–3.0 for standard PMDI grades.
Physical State: Pure 4,4′-MDI is a white to pale yellow solid at room temperature (Melting Point ~38°C), while PMDI is a dark brown liquid.
Viscosity: PMDI grades typically exhibit viscosities between 150 and 700 mPa·s at 25°C, influencing flow characteristics in molding applications.
Flash Point: High flash point (typically >200°C), contributing to a stable safety profile for bulk storage and transport.
Specific Gravity: Approximately 1.20 to 1.24 g/cm³ at 25°C.

Download Technical Data Sheet (TDS)

Practical industry uses

Applications

Building & Construction: The primary ingredient in rigid PUR and PIR insulation boards, spray polyurethane foam (SPF), and structural insulated panels.
Refrigeration: Used as the insulating core for domestic refrigerators, commercial freezers, and refrigerated transport containers.
Automotive Industry: Employed in the manufacture of high-resilience seating, instrument panels, bumpers, and sound-dampening components.
Wood Binders: Acts as a high-performance, formaldehyde-free adhesive for oriented strand board (OSB) and medium-density fiberboard (MDF).
CASE Sector: Vital for formulating high-performance Coatings, Adhesives, Sealants, and Elastomers used in harsh industrial environments.
Footwear: Used to produce lightweight, microcellular foam outsoles for athletic and safety shoes, offering excellent shock absorption.