Liquid polysulfide polymers with thiol end groups are the base polymer for flexible sealants used in aerospace fuel tanks, insulating glass units, marine decking and construction joints. The most widely referenced grade in this family is Thioplast® G1 from Nouryon. Alfa Chemical supplies an equivalent grade, AL-2, from Zhengzhou, China. Both share the same CAS 68611-50-7 and overlapping property ranges.
This article compares AL-2 and Thioplast® G1 using public technical data, explains what "performance equivalent" means in practice, and provides a substitution checklist for formulators evaluating a second source.
What CAS 68611-50-7 Covers
CAS 68611-50-7 covers a family of liquid polysulfide polymers, not a single molecular structure. The polymer is produced by reacting 1,2,3-trichloropropane with 1,1′-[methylenebis(oxy)]bis[2-chloroethane] and sodium sulfide. The result is a thiol-terminated liquid polymer with a backbone containing disulfide linkages.
The molecular formula C₈H₁₅Cl₅Na₂O₂S represents a repeating unit, not the full polymer chain. Typical number-average molecular weights range from 1,000 to 8,000 g/mol, depending on the grade. The thiol (–SH) content and the branching level (controlled by trichloropropane content) determine cure speed, crosslink density and final mechanical properties.
Property Comparison: AL-2 vs Thioplast® G1
The table below compares typical literature values for both grades. Alfa Chemical batch-specific values are reported in the COA. Confirm with us before formulation.
| Property | AL-2 (Alfa Chemical) | Thioplast® G1 (Nouryon) | What It Means for Substitution |
|---|---|---|---|
| Molecular weight (g/mol) | 3,500–4,600 | 3,400–4,600 | Overlapping ranges. AL-2 covers the same MW window. |
| Thiol content (%) | 1.7–2.0 | 1.8–2.0 | AL-2 includes G1's range. Cure stoichiometry follows the same rule. |
| Viscosity (Pa·s, 25°C) | 41–48 | 38–50 | AL-2 sits inside G1's range. Pump and mixing behavior should be similar. |
| Branching (mol% TCP) | 2.0 | 2.0 | Same crosslink density. Cure speed and final modulus should match. |
| Water content (%) | ≤0.3 | ≤0.5 | AL-2 is tighter on moisture. This matters for aerospace and insulating glass. |
Reference data: Nouryon Thioplast® G1 product data sheet (2025); patent EP1077228A1 for LP-2 characteristics. Alfa batch-specific values are reported in the COA.
What "Performance Equivalent" Means in Practice
AL-2 is not a chemical copy of Thioplast® G1. Both are thiol-terminated liquid polysulfide polymers covered by the same CAS number, with overlapping molecular weight, thiol content, viscosity and branching. "Performance equivalent" means that a formulation developed with G1 should produce comparable cured properties when AL-2 is substituted at the same stoichiometry, without a full reformulation.
The substitution is not automatic. Three factors determine whether a direct swap will work:
1. Cure stoichiometry. Thiol content drives the MnO₂ ratio. If the AL-2 batch COA reports a thiol content at the lower end of the range (1.7%), the MnO₂ loading may need a small upward adjustment. The recommended MnO₂ range for both grades is 6–15 parts per 100 parts polymer, with 6 parts being the common starting point for high-performance sealants.
2. Moisture sensitivity. AL-2 has a tighter water specification (≤0.3% vs ≤0.5% for G1). For moisture-sensitive applications such as insulating glass secondary seals, this is an advantage, not a barrier. For applications where G1's higher moisture tolerance is acceptable, AL-2's tighter spec does not create a processing problem.
3. Viscosity window. AL-2's viscosity range (41–48 Pa·s) is narrower than G1's (38–50 Pa·s). If your current process is optimized for a G1 batch at the low end of the viscosity range (38–40 Pa·s), an AL-2 batch at 41–48 Pa·s may require a small adjustment in mixing time or plasticizer loading. This is a minor adjustment, not a reformulation.
Cure Behavior: What to Expect When Swapping Grades
Both AL-2 and Thioplast® G1 cure by oxidation of terminal thiol groups. MnO₂ is the standard curing agent for sealant formulations. Lead dioxide (PbO₂) is also used but is less common in modern formulations. The cure reaction converts the liquid polymer into a crosslinked elastomer with disulfide and polysulfide linkages in the backbone.
In a typical two-component sealant system, Part A contains the liquid polysulfide polymer, fillers, plasticizers and adhesion promoters. Part B contains the MnO₂ curing paste. The mix ratio is often 10:1 by weight, but the exact ratio depends on the thiol content of the polymer and the MnO₂ concentration in the paste. Formulators using G1 should verify the mix ratio against the AL-2 batch COA before running a production trial.
Working life can be adjusted by the accelerator level. Diphenylguanidine and similar accelerators are commonly used at 0.1–0.5 parts per 100 parts polymer. Stearic acid at approximately 0.5 parts per 100 parts polymer can extend working life by about 2 hours without significantly affecting final cure.
Application Scenarios Where Substitution Is Common
Insulating Glass Secondary Seal
AL-2's tighter water specification (≤0.3%) and overlapping viscosity range make it a direct substitution for G1 in dual-glazed unit secondary seals. Low moisture vapor transmission is the critical performance requirement.
Aerospace Fuel Tank Sealant
Both grades are used in flexible sealants requiring fuel resistance and high tensile strength. The 2.0 mol% TCP branching matches G1, so crosslink density and cured modulus should be comparable. Qualification testing per customer specification is required.
Construction Joint Sealant
AL-2 and G1 are both used in high-tensile-strength, UV-resistant sealants for building facades and concrete joints. The substitution does not affect weathering performance.
Marine and Pipeline Sealing
Chemical resistance to oil, fuel and seawater is inherent in the polysulfide backbone, not grade-specific. Both grades perform similarly in marine deck and pipeline joint applications.
Market Context: Why a Second Source Matters
The global liquid polysulfide polymer market was valued at approximately US$151 million in 2025 and is forecast to reach US$197 million by 2032, growing at a CAGR of 3.9%. Building and construction is the largest end-use segment at about 67%, followed by aerospace at about 24%.
The top four producers hold approximately 94% of the global market share, with Nouryon being the largest at approximately 54%. This concentration means that a supply disruption at a single producer can affect the entire downstream sealant industry. For formulators and procurement teams, qualifying a second source is a supply-chain risk management decision, not just a cost decision.
Substitution Checklist for Formulators
Before swapping Thioplast® G1 for AL-2 in a qualified formulation, review these four items. They cover the variables that most often cause a substitution trial to fail.
1. Compare batch COAs side by side. Check molecular weight, thiol content, viscosity and water content. The AL-2 batch values should fall within or overlap the G1 range you are currently using.
2. Recalculate the MnO₂ ratio. Use the thiol content from the AL-2 COA, not the typical range. A 0.1% difference in thiol content changes the stoichiometric MnO₂ requirement.
3. Run a small-scale mix trial. Prepare a 1–5 kg batch using the same filler, plasticizer and accelerator package. Measure working life, cure speed and cured hardness. Compare against your G1 baseline.
4. Verify adhesion on the target substrate. Polysulfide sealants are often used with adhesion promoters. Run a peel or tensile bond test on the actual substrate before production scale-up.
How Alfa Chemical Supports Substitution Trials
Alfa Chemical supplies AL-2 (liquid polysulfide polymer, CAS 68611-50-7) from Zhengzhou, China. AL-23, AL-32 and AL-3 are also available for formulations requiring different molecular weights or branching levels.
For substitution trials, we provide batch-specific COA with actual molecular weight, thiol content, viscosity and water content. Research samples are available for lab evaluation. Our technical team can review your current formulation and recommend the MnO₂ ratio and accelerator level based on the AL-2 batch COA.
Share your target application, current G1 batch properties and processing conditions. We will help you determine whether a direct substitution is feasible or whether a small adjustment is needed. For general background on polysulfide chemistry, visit our knowledge base.
Need AL-2 for a substitution trial?
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Disclaimer: For research and industrial use only. Not for therapeutic, diagnostic, food, or cosmetic use without specific regulatory compliance. Thioplast® is a registered trademark of Nouryon. Alfa Chemical is not affiliated with Nouryon. Property data references public literature and product data sheets (Nouryon Thioplast® G1 PDS 2025; patent EP1077228A1). Alfa batch-specific values are reported in the COA. Confirm against the batch COA before use. Final sealant performance depends on formulation, curing agent and application conditions.