Polymers degradation half-life

Figure 8.38. Comparison of the effects on fractional incremental oil recovery of polymer degradation half-life for areal and cross-sectional polymer floods (Clifford and Sorbie, 1985).

NMR studies15 1 1 on polymers prepared with, 3C-labeled BPO have shown that the primary benzoyloxy and phenyl end groups formed by tail addition to monomer are thermally stable under conditions where the polymer degrades. They persist to > 50% weight loss at 300°C under nitrogen. Thus, these groups are unlikely to be directly responsible for the poor thermal stability of PS prepared with BPO as initiator. On the other hand, the secondary benzoate end groups, formed by head addition or transfer to initiator, appear extremely labile under these conditions. Their half life at 300°C is <5 min. 

The half-life of M-MT is dependent on the binding affinity of thionein for different metal ions. For instance, upon oxidation, Cu-MT forms insoluble polymers which are biologically unavailable and are eventually eliminated via biliary secretion. In contrast, thionein has lower affinity for Zn, making it more easily released from the protein and rendering the ion available for cellular processes. Furthermore, the rate of degradation may be influenced by differences in metal distribution between MT isoforms. It has been determined that MT degradation can occur in lysosomal and nonlysosomal (cytosolic) compartments. 

Constitutive poly(ADP-ribose) is degraded in a biphasic manner in intact cells with reported half-lives of about 5 minutes and one to several hours. When polymer levels are enhanced by experimentally activating the polymerase, the polymer is turned over rapidly with a half-life measured in minutes or even less. 

The first polymer-drug conjugate to be tested in humans for anticancer therapy is doxorubicin coupled with iV-(2-hydroxypropyl)methacrylamide copolymer via a linker that is degraded in lysosomes, thereby releasing the drug [29]. In contrast to the free drug doxorubicin, which has a distribution half-life of 0.08 h and an elimination half-Ufe of 30 h (see Table 8.6), the doxorubicin conjugate has a distribution half-life of 1.8 h and an elimination half-life of 90 h. 

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