Potential New Chemistries

Although they do not appear to have been investigated in aromatic polyesters, there are a few other antioxidant types which might prove useful in this regard. 

Classed by Marin and co-workers [27] as a moderate CB-D antioxidant, the use of HP-136 (or the previous packages containing the same) in PET and related polyesters may be worth investigating. 

Hydroxylamines [25] have the advantage that they are almost completely colourless, unlike the aromatic amines which are coloured, and the hindered phenols which form highly coloured breakdown species. This class of additive is exemplified by N,N-di(hydrogenated tallow)hydroxylamine (Irgastab FS-042 Ciba). This type of additive appears to operate as a radical scavenger and as a peroxide decomposer. Nitrones formed by oxidation of the hydroxylamine are also said to be stabilisers. Patents claim these additives as useful in reducing aldehyde content in polyester [28, 29], but there does not appear to have been any systematic study of their antioxidant capabilities in aromatic polyesters. 

Vitamin E (a-tocopherol) [30] is another potential candidate for an antioxidant in polyesters, and is available as a polymer additive from Hoffmann-La Roche as Ronotec 201. It has been shown that this additive can react with peroxy and alkyl radicals, and can trap more than one radical. The potential drawbacks may be the volatility and/ or thermal stability of this additive. 

As well as being excellent UV stabilisers for several polymer applications, there is ample evidence [31] to suggest that hindred amine light stabilisers can also operate as thermal antioxidants. Discussion of these additives will be undertaken in Chapter 8. 

---