In optical coating and adhesive formulations, refractive index control directly affects interfacial reflection and light transmission. LM-502 is a difunctional fluorine-modified UV monomer designed around a low refractive index, low viscosity, and adhesion to a range of substrates. It is suitable for optical fiber coatings, anti-reflective films, anti-glare films, and UV adhesives for optical display materials.
Compared with monofunctional low-refractive-index monomers, the difunctional structure of LM-502 offers a different balance between cure crosslink density and cured-film properties. This makes it a useful option for formulators who need to adjust refractive index while maintaining a certain level of network formation.
Typical Properties
| Property | Typical Value |
|---|---|
| Functionality | Difunctional |
| Refractive index (nD 25) | 1.360 |
| Viscosity at 25°C | 10 mPa·s |
| Tg | 50°C |
| Molecular weight (GPC) | 170 |
| Color (Gardner) | 2 |
| Acid value | ≤ 1 mg KOH/g |
| Effective content | 100% |
The refractive index of 1.360 places LM-502 in the low-refractive-index range for fluorine-modified UV materials. For reference, low-refractive-index materials used in optical fiber cladding typically need to be below that of silica core (n ≈ 1.46) by at least 0.01–0.02, and some fluorine-substituted acrylate monomers are designed for ≤ 1.40 or even ≤ 1.35. Within this framework, LM-502 provides usable room for refractive index reduction.
Difunctionality Combined with Low Viscosity
Fluorine-modified monomers generally reduce refractive index through the low molar refraction contribution of fluorine atoms. On this basis, the distinguishing feature of LM-502 is its combination of functionality and viscosity.
Difunctionality means the molecule contains two reactive sites for UV free-radical polymerization. Compared with monofunctional monomers, it can form a certain degree of crosslinked network during cure, which may contribute to solvent resistance and mechanical integrity of the cured film. Its Tg of 50°C is higher than many conventional low-refractive-index monofunctional monomers, and this difference may affect the balance between hardness and flexibility of the cured coating.
A viscosity of 10 mPa·s at 25°C is relatively low, making the monomer suitable as a reactive diluent in formulations to improve leveling and substrate wetting. Low viscosity also provides a process window for precision coating methods such as spin coating, spraying, and dip coating. It should be noted that higher functionality is often accompanied by a greater tendency toward cure shrinkage, so the actual formulation still needs to be evaluated together with the specific resin system.
Main Application Scenarios
Optical Fiber Coatings
Optical fiber coating systems require low-refractive-index materials that can work with the core and adjacent coating layers to help maintain the optical conditions needed for signal transmission. As a fluorine-modified UV monomer, LM-502 can be used as a low-refractive-index component in optical fiber coating formulations. Its low viscosity and good wetting and leveling behavior help the coating liquid spread evenly on the fiber surface and support continuous coating processes that require flow and cure speed. In practice, the monomer can be combined with conventional UV resins and monomers, but the ratio should be tested against adhesion, flexibility, and cure conditions.
Anti-Reflective and Anti-Glare Films
Anti-reflective and anti-glare films often require a low-refractive-index component in UV-curable coatings to adjust optical performance and reduce interfacial reflection. The low refractive index of LM-502 makes it suitable as a diluent monomer or low-refractive-index component in such coating formulations. Its low viscosity and leveling behavior also help improve coating uniformity and support surface appearance and adhesion. Formulators should still evaluate compatibility and final optical performance against target film thickness, substrate type, and cure process.
UV Adhesives for Optical Displays
In optical display bonding, the degree of refractive index matching between the adhesive layer and adjacent materials affects interfacial reflection and overall light transmission. LM-502 can be used in UV adhesive formulations as a low-refractive-index monomer component to help adjust the optical properties of the adhesive layer while contributing to adhesion and cure efficiency. For optical display bonding, formulators typically need to consider light transmission, low refractive index, cure shrinkage, and durability together, so this monomer is best treated as one formulation option and validated through testing with the actual resin, monomer, and additive system.
Application Positioning Summary
Overall, LM-502 is positioned for applications that require low-refractive-index UV materials: optical fiber coatings, anti-reflective and anti-glare films, and UV adhesives for optical displays. Its low viscosity, wetting and leveling behavior, and fluorine-modified low refractive index provide formulators with an optional monomer for dilution, leveling, and optical adjustment. Final performance should be verified against the specific substrate, cure conditions, and companion formulation.