Bifunctional UV monomer

As the name suggests, bifunctional UV monomers are molecules containing two reactive functional groups that participate in photopolymerization reactions. These functional groups are typically acrylates or methacrylates, with acrylates dominating the current market due to their superior reactivity and cost-effectiveness. Compared to their monofunctional counterparts, bifunctional UV monomers offer several advantages: Faster curing speed,Higher crosslinking density in the cured film,Good dilution properties,Reduced volatility and lower odor.

Below is an overview of some commonly used difunctional UV monomers:

I. DPGDA/TPGDA

These two UV monomers belong to Propylene Glycol Diacrylate.

DPGDA: Dipropylene Glycol Diacrylate.

DPGDA is characterized by low volatility, low viscosity, good dilution capability, fast curing.

TPGDA: Tripropylene Glycol Diacrylate.

TPGDA has one more propoxy than DPGDA, better flexibility, slightly lower viscosity, better dilution, faster curing, reduced skin irritation, lower price.TPGDA is among the most widely used difunctional monomers in UV-curable formulations.

II. HDDA

HDDA: 1,6-Hexanediol Diacrylate.

HDDA is known for its low viscosity, strong dilution and excellent compatibility with various resins, good adhesion to plastic substrates and improved flexibility of cured films. Compared with TPGDA, HDDA is more irritating to the skin and a bit more expensive.

Ⅲ. NPGDA/2PO-NPGDA

These two UV monomers belong to Neopentyl Glycol Diacrylate.

NPGDA: Neopentyl Glycol Diacrylate.

NPGDA exhibits low viscosity, good dilution, high reactivity, high Tg, fast curing speed, but skin irritation.

2PO-NPGDA: Propylene Oxide Neopentyl Glycol Diacrylate.

The addition of propylene oxide group improves the skin irritation of NPGDA, and its cured film has high tensile strength, good elongation and low shrinkage.

IV. Ethoxylated BPADA

Common variants include 2EO-BPADA, 4EO-BPADA, and 10EO-BPADA.  

By introducing ethoxy groups between the bisphenol A unit and the acrylate groups, the molecular structure becomes similar to that of bisphenol A epoxy acrylate, as both contain a bisphenol A structure. This imparts the material with high hardness, a high refractive index, excellent heat resistance, and chemical resistance.

Standard bisphenol A epoxy acrylate contains two bisphenol A units and has a room-temperature viscosity in the range of tens of thousands of centipoise (cps). In contrast, ethoxylated bisphenol A acrylate contains only one bisphenol A group, resulting in a much lower room-temperature viscosity of approximately 1,000 cps — significantly lower than that of bisphenol A epoxy acrylate. Moreover, as the number of ethoxy groups increases, the viscosity decreases further, while the flexibility and hydrophilicity of the cured film improve accordingly.

V. PEGDA

PEGDA: Polyethylene Glycol Diacrylate.

PEGDA is available in different molecular weights, including PEG(200)DA, PEG(400)DA, and PEG(600)DA. . Their cured films are soft, with medium tensile strength and elongation at break. With the increase of molecular weight, viscosity and flexibility rise together, while Tg and skin irritation decrease and hydrophilicity increases. Additionally, hydrophilicity improves — truly like a girl growing into a woman, becoming gentler with time.

The above are common difunctional UV monomers.