page_title: Polymer stabilizers
section_title: Secondary antioxidants (hydroperoxides scavengers)
hierarchical_section_title: Polymer stabilizers / Antioxidants / Secondary antioxidants (hydroperoxides scavengers)
caption_attribution_description: English: Structure of 31570-04-4
context_page_description: Stabilizers are a class of chemical additives commonly added to polymeric materials, such as plastics, to inhibit or retard their degradation. Polymers can be subject to various degradation processes, including oxidation, UV-damage, thermal degradation, ozonolysis, combinations thereof such as photo-oxidation, as well as reactions with catalyst residues or other impurities. These processes all degrade the polymer on a chemical level, leading to chain scission that can adversely affect its mechanical properties such as strength and malleability, as well as its appearance and colour.
  A vast number of chemically distinct polymers exist, with their degradation pathways varying according to their chemical structure, as such an equally wide range of stabilizers exists. The market for antioxidant stabilisers alone was estimated at US$1.69 billion for 2017, with the total market for all stabilizers expected to reach US$5.5 billion by 2025.
  Organic materials deteriorate over time due to the effects of light, atmospheric oxygen, and other environmental factors. Degradation of plastics can cause discoloration and embrittlement. Stabilizers counteract these processes.
context_section_description: Secondary antioxidants act to remove organic hydroperoxides (ROOH) formed by the action of primary antioxidants. Hydroperoxides are less reactive than radical species but can initiate fresh radical reactions:
  ROOH + RH → RO• + R• + H₂O
  As they are less chemically active they require a more reactive antioxidant. The most commonly employed class are phosphite esters, often of hindered phenols e.g. Tris(2,4-di-tert-butylphenyl)phosphite. These will convert polymer hydroperoxides to alcohols, becoming oxidized to organophosphates in the process:
  ROOH  +  P(OR')₃  →   OP(OR')₃  +  ROH
  Transesterification can then take place, in which the hydroxylated polymer is exchanged for a phenol:
  ROH + OP(OR')₃  →   R'OH + OP(OR')₂OR
  This exchange further stabilizes the polymer by releasing a primary antioxidant, because of this phosphites are sometimes considered multi-functional antioxidants as they can combine both types of activity.
  Organosulfur compounds are also efficient hydroperoxide decomposers, with thioethers being particularly effective against long-term thermal aging, they are ultimately oxidise up to sulfoxides and sulfones.
caption: Tris(2,4-di-tert-butylphenyl)phosphite, a phosphite widely used as a secondary antioxidant in polymers.
exif: {}