Degradation rate of polymers

Aoki M, Uchida H, Watanabe M (2005) Novel evaluation method for degradation rate of polymer electrolytes in fuel cells. Electrochem Commun 7 1434-1438... 

Outright, D. E, Hunsuck, E E and Beasley, J. D., Degradation rates of polymers and copolymers of polylactic and polyglycolic acids. Oral Surgery, 142-152 (1974). 

Since much is known about the degradation mechanisms and degradation rates of polymer materials, and how these can be reduced or prevented (Fig. 21.3), it seems reasonable to use this knowledge ... 

C. Other Factors Affecting Photochemical Degradation Rates of Polymers... 

The effect of stress on the fliermal degradation rates of polymers can be fitted to an empirical Arrhenius-like equation that is attributed to Zhmkov rate = Aexp[-(AG Bo)/RT], where AG is an apparent activation energy, o is the stress, and A and B are constants. It has been suggested that an equation similar to the Zhurkov equation might apply in photodegradation ( )obs = Aexp[ (AG Bo)/RT]. The Zhurkov equation is empirical and does not fall strictly into any of the three... 

Based on these studies, it is obvious that poly(N-acylhydroxy-proline esters) are very slowly degrading polymers. These materials may therefore be useful for long-term applications, such as implantable, multiyear contraceptive formulations. For such applications the degradation rates of poly (lactic acid)/poly (glycolic acid) devices would probably be too rapid. 

Increase the oxidation rate of polymers, e.g. metal ions which increase the hydroperoxide decomposition rate. Photodegradation and thermal degradation are enhanced by transition metal ion containing pro-oxidants, such as iron dithiocarbamate (as opposed to nickel dithiocarba-mate, which acts as a photo-antioxidant). 

Figure 27 shows that the PC is stable up to about 400°C the maximum rate of polymer degradation occurs at 500°C a residue of 20% remains at 800°C [69]. In the degradation step occurring at 500°C some of the many ions (m/z) that may be identified are phenol at 94 methylphenol at 108 isopropylidenephenol,... 

The erosion of copolymers requires the hydrolytic cleavage of three bond types the A A bond, the A-B bond, and the B-B bond. If the degradation rates of these three bonds are unequal, as is likely the case, then the erosion will be inhomogeneous. And, if drugs are inhomogene-ously distributed in the polymer matrix, the drug release profile will not follow overall device erosion (Shen et al., 2002). Therefore, it is necessary to accurately describe the microstructure of microphase-separated systems. 

Molecular weight may also affect the erosion rate. Table IX shows the degradation rate of a representative poly(anhydride-co-urethane), a poly(anhydride-co-amide), and a poly(anhydride-co-ester) of different molecular weights (Hartmann et al., 1993). For all of these polymers reported, the erosion rate decreases as the molecular weight increases. 

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