Poly during degradation

In contrast to all other known poly(3HB)-degrading bacteria poly(3HB) depolymerase production by P. lemoignei is maximal during growth on succinate... 

Fig. 37. Production of A carbon dioxide, propene and n-propanol during degradation of poly(n-propyl acrylate) [114].

Polystyrene also forms miscible blends with PPE in which the hydrogen-transfer reaction of PS is rendered less effective due to the PPE component [Jachowicz et al., 1984]. In contrast, poly(a-methyl styrene) blends with PPE, although also reported miscible, show no evidence of any interactions during degradation. Head-to-head and head-to-tail PS structures were found to behave (hfferentiy [JCryszewski, et al., 1982]. 

The unzipping or zip length S gives the number of monomer molecules eliminated per kinetic chain. Low values of S mean that little monomer is eliminated, but not necessarily that there is little degradation [compare, for example, the zip length of poly(styrene) (Table 23-4) with that of the products formed during degradation (Table 23-3)]. 

Polyesters also have a major disadvantage. Most of them degrade by a bulk degradation mechanism," " which leads to the accumulation of acidic prodncts within the polymer bulk that can cause late non-infectious inflammatory responses when released in a sudden burst upon stractuie breakdown." An inflanunatory response to poly(cr-hydroxy acids) was also found to be triggered by the release of small particles during degradation... 

Intrinsically amorphous poly(DL-Lactide) or PLA50 is taken as example. The samples are initially transparent (Fig. 2.3(a)), in agreement with their amorphous state. They become gradually whitish during degradation due to water uptake. After 5 weeks, the cross-section of the specimens appears heterogeneous the surface layer is rigid and whitish, and the interior becomes a very viscous liquid (Fig. 2.3(b)). Finally after 12 weeks, only an emptied shell remains (Fig. 2.3(c)). 

Figure 2.20 Weight loss changes of amorphous PLAio, PLA25, and PLA40 during degradation in the presence of proteinase K. PLA, poly(lactic acid).

Figure 3.10 Scheme of poly-s-caprolactone polymeric chain cleavage during degradation. 

With recent improvements in resolution it has become possible to use GPC to characterize polymers of low molar mass and to examine polymer additives. Eisenbeiss et have reviewed applications of GPC in analysis of additives and surfactants in polymers. Coulombe et used GPC to study oligomers formed during degradation of poly( -hydroxybutyratc) and Kumlin et n/. ... 

As mentioned previously, the exposure of poly(vinyl chloride) to either ultraviolet light or heat leads to degradation, as a result of which discoloration and changes in mechanical properties can occur. The degradation of poly(vinyl chloride) has been the subject of extensive investigation and much information has accumulated. However, the reactions which take place are complex and are not completely understood at the present time. The principal processes which occur during degradation are dehydrochlorination and oxidation and these are now considered. 

Figure 8.16 Mass loss of the poly(triol a-ketoglutarate) bioelastomers such as PGa, PBa and PHa during degradation in phosphate buffer solutions (pH = 7.4, 37 °C) under the conditions of different curing temperature and time. Adapted from Barrett and Yousaf...

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