Antioxidant 605 is a phosphite-based secondary antioxidant used to protect polymers and related formulations from oxidative damage, especially during heat-intensive processing. In this guide, the name Antioxidant 605 refers to diisodecyl pentaerythritol diphosphite (CAS 26544-27-4), a phenol-free phosphorus stabilizer also sold under other trade or grade names. Its main role is to decompose hydroperoxides formed during oxidation, helping reduce discoloration, molecular degradation, loss of mechanical properties, and processing instability. It is commonly considered for plastics, polyurethane systems, resins, coatings, adhesives, and other polymer applications, often in combination with a primary antioxidant for broader protection.
| Question | Quick Answer |
| What is Antioxidant 605? | A secondary phosphite antioxidant and processing stabilizer; commonly associated with CAS 26544-27-4. |
| Main function | Decomposes hydroperoxides and helps interrupt oxidative degradation during processing and service. |
| Typical chemistry | Diisodecyl pentaerythritol diphosphite; phosphite ester. |
| Typical form | Commercial grades are commonly supplied as a clear to lightly turbid liquid. |
| Where is it used? | Polymer processing, PVC, polyurethane, resins, coatings, adhesives, and stabilizer packages. |
| How is it normally formulated? | Frequently paired with a primary hindered phenolic antioxidant; exact dosage must be validated for the specific grade and formulation. |
Product Overview
What Is Antioxidant 605?
Antioxidant 605 is generally described in the polymer-additives market as a liquid phosphite antioxidant based on diisodecyl pentaerythritol diphosphite. Phosphite antioxidants belong to the secondary-antioxidant family. Unlike primary antioxidants, which are mainly designed to intercept free-radical chain reactions, secondary antioxidants focus on reactive peroxide species generated as polymers oxidize. This makes Antioxidant 605 especially relevant to processing stabilization, where heat and oxygen can accelerate degradation before a finished product even enters service.
Commercial naming is important here. The number “605” is not a universal chemical nomenclature, and different suppliers may use their own grade numbers. For technical purchasing, quality control, and regulatory review, buyers should therefore verify the CAS number, chemical name, TDS, SDS, specification, and batch COA rather than relying only on the trade number. In this article, Antioxidant 605 refers specifically to CAS 26544-27-4.
| Property | Typical / Reference Information |
| Chemical name | Diisodecyl pentaerythritol diphosphite |
| CAS number | 26544-27-4 |
| Antioxidant class | Secondary antioxidant / phosphite processing stabilizer |
| Molecular formula | C25H50O6P2 |
| Molecular weight | Approximately 508.6 g/mol |
| Typical physical form | Colorless transparent to lightly turbid liquid, depending on grade |
| Key stabilization role | Hydroperoxide decomposition, processing stabilization, and color protection |
Read more: Antioxidant 405 | Performance and Industrial Uses
How Antioxidant 605 Works
Oxidative degradation in polymers is usually a chain process. Heat, shear, residual catalyst species, oxygen, or other stresses can generate reactive radicals. These radicals react with oxygen and can form hydroperoxides. Hydroperoxides are unstable intermediates; if they decompose into additional radicals, degradation can accelerate and lead to chain scission, crosslinking, viscosity changes, yellowing, brittleness, and a decline in mechanical performance.
A phosphite antioxidant such as Antioxidant 605 is used to react with hydroperoxides before they generate more destructive radical species. This peroxide-decomposition role is why phosphites are often described as secondary antioxidants. In practice, formulators commonly combine them with primary hindered phenolic antioxidants. The two antioxidant families act at different stages of the oxidation cycle, so a properly designed package can offer stronger processing protection and better retention of properties than relying on one mechanism alone.
This distinction also helps explain why Antioxidant 605 should not simply be described as a universal “long-term antioxidant.” Its most important value is often seen during manufacturing, compounding, polymer synthesis, extrusion, molding, or other thermal-processing steps. The final stabilization package, polymer type, processing temperature, residence time, exposure conditions, and required service life determine whether additional primary antioxidants, light stabilizers, UV absorbers, or other additives are needed.
Benefits
Improved Processing Stability
One of the central reasons to use Antioxidant 605 is to limit oxidation while polymers are exposed to elevated temperatures. Processing can place a material under simultaneous thermal, mechanical, and oxidative stress. By reducing the concentration of reactive hydroperoxides, a phosphite stabilizer can help control degradation during these stages and support more consistent processing behavior.
Better Color Retention
Oxidation and thermal degradation can create colored by-products or trigger visible yellowing in sensitive polymer systems. Manufacturer literature for CAS 26544-27-4 emphasizes color improvement and non-discoloring stabilization as important attributes. This is relevant to clear, light-colored, white, or appearance-sensitive materials where even small color shifts can affect product acceptance.
Support for Mechanical Property Retention
Oxidation can alter polymer molecular weight and structure. Depending on the resin, this may contribute to embrittlement, strength loss, reduced elongation, unwanted viscosity changes, or other performance problems. Antioxidant 605 does not mechanically reinforce a polymer by itself, but by reducing oxidative reactions it can help preserve the molecular integrity needed for the material to retain its intended properties.
Read more: Antioxidant 1035 | Features and Industrial Applications
Synergy with Primary Antioxidants
A major formulation advantage of secondary phosphite antioxidants is their complementary action with primary antioxidants. Hindered phenolics are designed mainly to interrupt radical propagation, while phosphites address hydroperoxides. Combining these mechanisms can improve overall stabilization efficiency when the ingredients are compatible with the resin and processing conditions. The appropriate ratio should be selected through formulation testing rather than copied from an unrelated application.
Phenol-Free Stabilization Option
Several commercial grades based on CAS 26544-27-4 are marketed as phenol-free phosphite stabilizers. This can be valuable in formulations where manufacturers want to avoid free phenolic residues from the secondary-antioxidant component. However, “phenol-free” should be confirmed against the actual supplier specification and does not mean the total formulation contains no phenolic substances, particularly when Antioxidant 605 is intentionally paired with a hindered phenolic primary antioxidant.
| Potential Benefit | Why It Matters in Polymer Processing |
| Hydroperoxide decomposition | Helps prevent peroxide-derived radical formation and secondary degradation. |
| Thermal processing protection | Supports polymer stability during compounding, extrusion, molding, or synthesis. |
| Color protection | Can reduce heat-related yellowing or color drift in suitable formulations. |
| Synergistic stabilization | Works through a different mechanism from hindered phenolic primary antioxidants. |
| Formulation flexibility | Liquid phosphite grades can be convenient for metering and blending in some processes. |
Industrial Applications
The suitability of Antioxidant 605 depends on the exact commercial grade and the polymer system. References for CAS 26544-27-4 identify use across plastics and resin technologies, with particular relevance to formulations that need thermal stabilization, color protection, or peroxide decomposition. The following applications are common areas for technical evaluation.
PVC and General Polymer Stabilization
Phosphite stabilizers are used in PVC and other polymer systems as part of broader stabilization packages. In PVC applications, manufacturers of CAS 26544-27-4 grades describe benefits such as improved transparency, processing color, and heat resistance. The phosphite normally functions alongside the rest of the heat-stabilizer system rather than replacing all other stabilizers. Compatibility with plasticizers, metal stabilizers, lubricants, pigments, fillers, and processing aids should be confirmed during formulation trials.
Polyurethane Systems
Diisodecyl pentaerythritol diphosphite is also associated with polyurethane processing. Manufacturer references identify this chemistry as an antioxidant, heat stabilizer, non-discoloring stabilizer, and in some cases a scorch-retarding additive for polyurethane. This makes it relevant to PU formulations where thermal exposure during reaction or processing can cause premature color development or degradation. Final performance depends strongly on the polyol, isocyanate, catalyst, other additives, and cure profile.
Resins, Polyols, Epoxy Systems, and Coatings
CAS 26544-27-4 is used in resin-related applications where color stability and thermal stability are important. Supplier literature references unsaturated resins, polyols, epoxy systems, coatings, and similar high-molecular-weight materials. In these formulations, the antioxidant can be introduced to reduce oxidation during synthesis, processing, or subsequent heat exposure. Because resin chemistry varies widely, dosage and addition point should be established through laboratory and production-scale validation.
Adhesives and Specialty Formulations
The chemistry also appears in adhesive applications. PubChem records an FDA food-contact notification for CAS 26544-27-4 as an antioxidant in certain food-contact adhesives, under specified use limitations. This does not mean every Antioxidant 605 grade is automatically approved for food contact or that the same conditions apply globally. Food-contact, medical, electrical, automotive, or other regulated uses always require confirmation of the exact grade, applicable legislation, migration limits, customer specifications, and supporting supplier documentation.
| Application Area | Typical Reason for Evaluation |
| PVC | Processing color, transparency, and heat-stabilization support. |
| Polyurethane | Thermal stabilization, color control, and scorch/processing support in suitable systems. |
| Resins & polyols | Protection against oxidation during synthesis and later thermal exposure. |
| Epoxy & coatings | Color and heat-stability support in compatible formulations. |
| Adhesives | Oxidative stabilization; regulated uses require grade-specific compliance review. |
| Polymer additive packages | Secondary-antioxidant component used with primary antioxidants or other stabilizers. |
How Much Antioxidant 605 Should Be Used?
There is no single universal dosage for Antioxidant 605. Some suppliers of CAS 26544-27-4 grades publish broad starting ranges, but the correct treat rate depends on polymer type, thermal history, stabilizer package, target color, required service life, and processing conditions. A dosage that works in PVC may not be appropriate for polyurethane, an adhesive, or an epoxy formulation. The most reliable approach is to start from the current supplier TDS, run controlled laboratory trials, and evaluate color, melt stability, mechanical retention, aging performance, and any regulatory constraints before setting the production formulation.\
Read more: Antioxidant 3114 | High-Performance Thermal Stabilizer
Handling & Storage
Storage Recommendations
Phosphite antioxidants can be sensitive to moisture and prolonged exposure to unsuitable storage conditions. Commercial guidance for CAS 26544-27-4 generally recommends keeping the product in its original, tightly closed container in a dry, well-ventilated area, protected from moisture, excessive heat, and direct sunlight. Storage temperature and shelf life should follow the specific supplier TDS or SDS because packaging, purity, additives, and grade design can affect stability.
Safe Handling
Industrial handling should follow the current supplier Safety Data Sheet. Avoid unnecessary skin and eye contact, maintain appropriate workplace ventilation, and use personal protective equipment suitable for the task and local safety requirements. Do not assume that one online SDS applies to every product sold as Antioxidant 605; hazard classifications and precautionary statements may differ by supplier, composition, jurisdiction, or SDS revision. For transport and regulatory classification, use the documentation issued for the exact material being shipped.
Quality and Purchasing Checks
- Confirm the chemical name and CAS number instead of purchasing by the “605” grade number alone.
- Review the latest TDS and SDS for the exact supplier grade.
- Check the batch COA against agreed limits such as appearance, color, acid value, refractive index, specific gravity, or phosphorus content where relevant.
- Confirm packaging and storage requirements before shipment, especially for long transit times or hot climates.
- Validate compatibility and dosage in the customer’s polymer formulation before full-scale production.
- For regulated applications, verify compliance documents for the destination market and intended end use.
Frequently Asked Questions
Is Antioxidant 605 a primary or secondary antioxidant?
Antioxidant 605, when referring to diisodecyl pentaerythritol diphosphite (CAS 26544-27-4), is a secondary phosphite antioxidant. Its main stabilization mechanism is hydroperoxide decomposition rather than direct radical scavenging.
Can Antioxidant 605 be used with Antioxidant 1010?
Yes, secondary phosphites are commonly combined with hindered phenolic primary antioxidants such as Antioxidant 1010 when the formulation requires complementary stabilization mechanisms. The best ratio must be validated for the specific polymer and processing conditions.
Is Antioxidant 605 the same as Antioxidant 168?
No. Both are phosphite-type secondary antioxidants, but they are different chemicals. Antioxidant 168 is commonly tris(2,4-di-tert-butylphenyl) phosphite, CAS 31570-04-4, whereas the Antioxidant 605 discussed here is CAS 26544-27-4.
What polymers can use Antioxidant 605?
Supplier references for CAS 26544-27-4 include PVC, polyurethane systems, resins, polyols, epoxy materials, coatings, adhesives, and broader polymer-stabilizer packages. Suitability must still be confirmed for the exact grade and formulation.
Does Antioxidant 605 prevent UV degradation?
It is primarily an antioxidant and processing stabilizer, not a dedicated UV absorber or hindered amine light stabilizer. Outdoor or light-sensitive applications may require a separate UV-stabilization package in addition to antioxidant protection.
Is Antioxidant 605 food-contact approved?
Regulatory status is application- and grade-specific. CAS 26544-27-4 has an FDA food-contact notification for a defined adhesive use with specified limitations, but this should not be interpreted as a blanket approval for all polymers, all grades, or all countries.
Conclusion
Antioxidant 605 is best understood as a secondary phosphite stabilizer for controlling peroxide-driven oxidation during polymer processing and thermal exposure. When the name refers to diisodecyl pentaerythritol diphosphite (CAS 26544-27-4), it is valued for hydroperoxide decomposition, processing stability, color protection, and compatibility with multi-component antioxidant packages. Its strongest performance is usually achieved when it is selected as part of a complete stabilization strategy rather than treated as a stand-alone solution for every degradation mechanism.
For purchasing or formulation work, verify the exact CAS number and supplier grade, review the current TDS/SDS/COA, and validate the dosage under real processing conditions. This is particularly important because the commercial number “605” can be used differently across markets. A technically controlled selection process helps ensure that the antioxidant delivers the expected stability without creating compatibility, color, processing, or regulatory issues.
Natural internal-link sentence example: For formulations that require a combined stabilization system, compare the role of Antioxidant 1010 as a primary antioxidant with Antioxidant 168 and other phosphite-based secondary antioxidants before finalizing the additive package.
