Polymer degradation inhibition

Poly(L-malate) decomposes spontaneously to L-ma-late by ester hydrolysis [2,4,5]. Hydrolytic degradation of the polymer sodium salt at pH 7.0 and 37°C results in a random cleavage of the polymer, the molecular mass decreasing by 50% after a period of 10 h [2]. The rate of hydrolysis is accelerated in acidic and alkaline solutions. This was first noted by changes in the activity of the polymer to inhibit DNA polymerase a of P. polycephalum [4]. The explanation of this phenomenon was that the degradation was slowest between pH 5-9 (Fig. 2) as would be expected if it were acid/base-catalyzed. In choosing a buffer, one should be aware of specific buffer catalysis. We found that the polymer was more stable in phosphate buffer than in Tris/HCl-buffer. 

All these methods cannot totally inhibit polymer degradation. This is just a question of time, heat and exposure to light, water and other aggressive environments. 

Polyacrylic add polymers can inhibit luminal degradation of insulin and other large peptides by trypsin and chymobypsin. They have strong bioadhesive properties, iriuco utg the in situ absorption of insulin [42]. 

Stabilizer—A substance added to a polymer to inhibit the degrading effects of oxidizers, ultraviolet light, or electrical discharge. 

Hindered amine light stabilisers (HALS) are the main stabiliser type (as a scavenger to inhibit free radical chain propagation), while organo-nickel compoimds (as a quencher to prevent initiation of polymer degradation) are used for UV stabilisation. 

The term stabiliser is the comprehensive technological term used to describe the inhibition of polymer degradation. In practice it applies almost exclusively to the inhibition of peroxidation which, as seen above, can be initiated by mechanooxidation, by light or by transition metal ions. Stabilisers are thus antioxidants acting by one or more complementary mechanisms. 

Lee HJ, Chd MH, Kim TU, Yoon SC (2001) Accumulation of polyhydroxyalkanoic acid containing large amounts of unsaturated monomers in Pseudomonas fluorescens BM07 utilizing saccharides and its inhibition by 2-bromooctanoic acid. Appl Environ Microbiol 67 4963-4974 Lee WH, Azizan MNM, Sudesh K (2004) Effects of culture conditions on the composition of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) synthesized by Comamonas acidovorans. Polym Degrad Stab 84 129-134... 

Phosphites are also commonly used in combination with phenolic antioxidants to inhibit polymer degradation and to improve color (7). As in the case of thiosynergists, phosphites reduce hydroperoxides to the corresponding alcohols... 

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