Methylenediphenyl diisocyanate (MDI) For Polyester Polyol

MDI (Methylene Diphenyl Diisocyanate) is a commonly used isocyanate component that reacts with polyester polyols to produce polyurethane (PU) materials. The choice of MDI depends on the desired properties of the final product.

Types of MDI for Polyester Polyol

1. Pure MDI (4,4'-MDI)

• Used in high-performance elastomers, coatings, and adhesives.

• Provides excellent mechanical strength and chemical resistance.

• Example: 4,4'-Diphenylmethane diisocyanate (MDI-100)

2. Modified MDI (Liquid MDI, Prepolymers, or Carbodiimide-modified MDI)

• Improved processing (lower viscosity) and better compatibility.

• Used in flexible foams, shoe soles, and sealants.

• Example: MDI prepolymers (e.g., Isonate 143L, Mondur MLQ)

3. Polymeric MDI (PMDI, pMDI)

• Contains a mixture of MDI isomers and oligomers.

• Used in rigid foams (insulation panels) and some elastomers.

• Example: Mondur MR, PAPI 27

Why MDI is Used with Polyester Polyol?

• High Reactivity: MDI reacts efficiently with polyester polyols, forming strong urethane linkages.

• Mechanical Properties: Produces polyurethanes with superior tensile strength, abrasion resistance, and heat resistance compared to TDI (Toluene Diisocyanate).

• Versatility: Suitable for elastomers, adhesives, coatings, and microcellular foams.

Common Applications of MDI + Polyester Polyol

• Footwear: Durable shoe soles (EVA alternatives).

• Industrial Elastomers: Conveyor belts, rollers, gaskets.

• Adhesives & Coatings: High-performance bonding solutions.

• Automotive Parts: Bushings, seals, and vibration dampers.

Alternative Isocyanates

• TDI (Toluene Diisocyanate): More common in flexible foams but less compatible with polyester polyols.

• HDI (Hexamethylene Diisocyanate): Used in weather-resistant coatings (aliphatic, UV-stable).