2122-49-8 Polymerization Inhibitor 705

About Inhibitor 705 – Tri-(4-hydroxy-TEMPO)phosphite (THP)

CAS No.: 2122-49-8

Inhibitor 705, also known as Tri-(4-hydroxy-TEMPO)phosphite (THP), is a highly effective polymerization inhibitor widely used to prevent the unwanted polymerization of monomers and oligomers during storage, handling, and processing. Its function as a radical scavenger allows it to neutralize free radicals that initiate polymerization, thereby halting uncontrolled chain reactions.

Key Features and Mechanism

THP combines three 4-hydroxy-TEMPO units attached to a phosphite backbone, offering:

• High radical scavenging efficiency due to the well-known reactivity of TEMPO

• Enhanced molecular stability from the phosphite core

• Improved solubility from hydroxyl groups

• Low volatility, making it ideal for high-temperature applications

This structure makes THP effective across a range of polymerization systems, particularly where traditional inhibitors may decompose or evaporate.

Applications in the Polymer Industry

Alkenes & EVA Copolymers

THP is commonly used in the production of ethylene-vinyl acetate (EVA) copolymers, helping reduce gel formation and impurities, and ensuring better product quality.

Unsaturated Polyesters

In unsaturated polyester resins—used in fiberglass-reinforced plastics—THP helps maintain a consistent molecular weight distribution while minimizing solid byproducts.

Polyurethanes

THP prevents premature polymerization of isocyanates, improving foam stability and reducing defects in polyurethane production.

Additional Benefits

• Antioxidant Potential: THP has also been studied as an antioxidant, especially for scavenging peroxide radicals that cause oxidative degradation in polymers.

• Wide Solvent Compatibility: Soluble in various solvents, making it adaptable to multiple formulations.

• Thermal Stability: Suitable for demanding industrial environments due to its resistance to decomposition.

Considerations and Limitations

While THP offers numerous benefits, users should consider:

• Interaction with other stabilizers, which may affect performance

• Variations in effectiveness depending on the monomer type and polymerization conditions

• Potential toxicity, as degradation products from hydroxy-containing compounds may require safe handling and disposal

Conclusion

THP (CAS 2122-49-8) is a versatile, low-volatility polymerization inhibitor with excellent radical-scavenging properties. Its structure and thermal stability make it especially useful in alkene polymerization, unsaturated polyesters, and polyurethanes, with growing interest in its antioxidant potential. However, like all specialty chemicals, its use should be evaluated within the context of application-specific requirements and safety protocols.