Poly Beta relaxation

Scandola M, CeccomUi G, Doi Y (1990) Viscoelastic relaxations and thermal properties of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvaleiate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate). Int J Biol Macromol 12 112—117 Scharlemann JPW, Laurance WF (2008) How green are biofuels Sdence 319 43-44 Senior PJ, Dawes EA (1973) The regulation of poly-beta-hydroxybutyrate metabolism in Azotobacter beiqerinckii. Biochem J 134 225—238 Shah AA, Hasan F, Hameed A (2010) Degradation of poly(3-hydroxybutyrate-co-3-hydroxy-valerate) by a newly isolated Actinomadura sp. AF-555, from sod. Int Biodeterior Biodegrad 64 281-285... 

Water and low temperature (20-35 C) aging influence the dynamic mechanical properties of a poly(amide-imide). At concentrations below 2 weight percent, water contributes to a low temperature relaxation between -120 and -50 C. Above 2 weight percent the water influences the beta transition. The enthalpy of activation for the beta relaxation is dependent upon aging temperature and time. Aging temperatures closer to the beta transition temperature result in higher activation enthalpies for that dispersion. 

Based on the dielectric and dynamic mechanical data, it appears that water and small polar molecules contribute to three dispersions in this poly(amide-imide). One is the low temperature relaxation between -100 and 0°C. This may be a hydrogen bonded relaxation since the activation enthalpy was 30 kJ/mol. This occurs at concentrations of water ranging between 0 to 4 weight percent. Two, the dielectric relaxation between 0 and 70 C can probably be attributed to conductive contaminants whose mobility is dependent upon a minimum amount of water. Three, at high water concentrations, greater than 2 weight percent, the water/NMP contributes to the beta relaxations observed between 50 and 150 C. 

Garwe F, Schonhals A, Lockwenz H, Beiner M, SchrOter K and Donth E (1996) Influence of cooperative alpha dynamics on local beta relaxation during the development of the dynamic glass transition in poly(n-alkyl methacrylate)s. Macromolecules 29 247-253. 

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