- Category:
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Applicable Business AreasAdhesive manufacturer, Resist manufacturer
Target ApplicationsAcrylic adhesive, Resist, Hard coat, Craft resin
Acrylate Formulations: Thiol Curing Aid for Longer Pot Life and Lower Odor
Acrylate systems are a popular choice for adhesives, resists, hard coats and more, thanks to their high formulation flexibility. By their reaction mechanism, however, they are readily inhibited by oxygen—so in practice, extra measures are needed to avoid incomplete cure.
Purging the curing step with nitrogen is highly effective, but maintaining an oxygen-free environment is not always practical in production. A common alternative is to add a thiol, whose high radical-generating ability accelerates cure. Yet primary thiols, while fast-reacting, make pot life hard to maintain.
esonac offers a lineup of polyfunctional secondary thiol monomers. Thanks to their greater steric hindrance, secondary thiols react more gently than primary thiols—making them an effective curing aid for reconciling curability and pot life in acrylate formulations.
Resonac's polyfunctional secondary thiol monomers
| Grade | Chemical name | Sturucture |
|---|---|---|
| Karenz MT PE1 | Pentaerythritol tetrakis(3-mercaptobutyrate) |  |
| Karenz MT BD1 | 1,4-Bis(3-mercaptobutyryloxy)butane |  |
| Karenz MT NR1 | 1,3,5-Tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione |  |
| Karenz MT TPMB | Trimethylolpropane tris(3-mercaptobutyrate) |  |
Solution
A low-odor secondary thiol that extends pot life in acrylate formulations
Thiols work well as curing aids in acrylate formulations. As shown in Figure 1, a photoinitiator-derived radical (I·) abstracts hydrogen from the thiol to form a thiyl radical (RS·), which reacts with the acrylate double bond to generate a carbon radical (Eq. 1). The carbon radical propagates with acrylate monomer to build polymer (Eq. 2), while the thiol acts as a chain-transfer agent, regenerating a thiyl radical to start the next chain (Eq. 3).
Pot life is a key factor when tailoring a formulation to its application. Primary thiols are highly reactive and short-lived, whereas the secondary thiol Karenz MT PE1 offers a better balance of reactivity and stability for a longer pot life (Figure 2)—with the added benefit of lower odor.
Figure 1. Thiol–acrylate reaction mechanism
Figure 2. Viscosity change at 40 °C1)
1)Primary thiol: pentaerythritol tetrakis(3-mercaptopropionate) (PETMP); Acrylate: dipentaerythritol hexaacrylate (DPHA)
Features
Less Cure Failure from Oxygen Inhibition
When acrylic monomers polymerize in air, carbon radicals are trapped by oxygen to form peroxy radicals; because these are low in energy, they cause polymerization to stall (Figure 3(b)). Adding a thiol donates hydrogen to the peroxy radical and regenerates a higher energy thiyl radical, so polymerization continues uninterrupted (Figure 3(c)(d)). The effect is especially valuable for thin films around 1 μm, where oxygen inhibition is most pronounced.
Figure 3. IR imaging of absorbance at 1408 cm-1 across the film cross-section
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Sample composition
- Thiol：
Karenz MT PE1 (0 - 10 wt%) - Urethane acrylate (Shin-Nakamura, U-15HA)：
trimethylolpropane triacrylate (TMPTA) =1 :1 (by weight) - Photoinitiator：
Omnirad 184 (5 wt%)
- Thiol：
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Measurement conditions
- Micro-ATR imaging (Ge)
- Resolution 8 cm-1
- 256 scans
- Range 4000-900 cm--1 70 x 70 μm
- Effective pixel size：1.1 x 1.1 μm / Pixel
Updated: September 14, 2026
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