Thermal stability of polymeric materials

Diffusion of solutions of Cr, Co and Mn ions through a PTFE membrane allows for separation of Cr from the remaining ions. Thermal stability of polymeric materials is a significant consideration in many poly(phosphazene) applications. The kinetics of the thermal degradation of PTFE are best fit with a model requiring a two step initiation for depolymerization. These steps involve formation of defect units, such as =P(0)NH- and =P(0)N(CH2CFj)-, which become active centers for depolymerization. Mixed... 

The chemico-thermal stability of polymeric materials can be expressed by the mass loss at a particular temperature by thermogravimetry, since polymers are degraded by thermo-oxidative reactions. On the other hand, the thermal stability of the physical structure of materials is characterized by the softening temperature for... 

In this regard, thermogravimetric analysis (TGA) is known to be a powerful technique in the study of the thermal decomposition and thermal stability of polymeric materials [38, 39]. However, the potential of TGA to evaluate the thermo-oxidative stability of contemporary UHMWPE for orthopedic use remains mostly to be unveiled. 

Equation 8.20 defines the three factors effecting the thermal stability of polymeric materials the polymer chemical structure, characterised by the value, the polymer melt structure, characterised by the dimension A and the type (intensity) of oxidiser diffusion, connected with the structure and characterised by the exponent P [54, 55]. 

The thermal stability of these materials has been previously studied by Miyata (2) and Reichle ( 3). Upon heating, below 200°C, the Interlayer water is lost. Between 250°C and 500°C the materials dehydroxylate accompanied by the decomposition of the anion. Reichle (3) has shown that this process Is reversible up to 600°C, and takes place without exfoliation of the layers while maintaining the morphological structure of the hydroxide. In their layered form, these hydroxides have found wide use as anion exchangers (4 ), and sorbents for various hydrocarbon molecules (5) and water. Intercalation of heteropoly anions ( 6) and polymerized bidimensional silicate anions into the interlayer has also been reported ( 7). 

In this article the focus will be on the application of one-dimensional (1-D) and two-dimensional (2-D) spectral-spatial ESRI to the photo- and thermal degradation of poly(acrylonitrile-butadiene-styrene) (ABS) (19-55,58-63). The ESRI approach was applied to ABS because it represents a polymer that is exceptionally important in technological applications, yet is also vulnerable to photo- and thermal degradation, and can be used only in the presence of protective additives. Hindered amine stabilizers (HAS), for instance bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (Tinuvin 770, (8)), are added for stabilization of polymeric materials (101,102). 

JOSEPH D. MENCZEL PhD. a recognized expert in thermal analysis of polymers with some thirty years of industrial and academic experience, is Assistant Technical Director at Alcon Laboratories. He has researched more than 120 polymeric systems in which he studied calibration of DSCs, glass transition, nucleation, crystallization, melting, stability, mechanical and micromechanical properties of polymers, and polymer-water interactions. Dr. Menczel holds six patents and is the author of seventy scholarly papers. He is the author of two chapters in the book Thermal Characterization of Polymeric Materials In conducting DSC experiments, Dr. Menczel found a crystal/amorphous interface in semicrystalline polymers, which later became known as the rigid amorphous phase. He is also credited with developing the temperature calibration of DSCs for cooling experiments,... 

Budrugeac, P On the pseudo compensation effect due to the complexity of the mechanism of thermal degradation of polymeric materials, Polymer Degradation and Stability, 58 (1997), p. 69 - 76... 

Keep in mind that the original impetus for military support of polymeric chelate research had the development of thermally stable materials as its goal. Acetylacetone was found to be more stable at 266°C in vacuo than its chelates containing Cu(II), Ni(II), Co(II), Co(IlI), A1(III), Cr(III). Fe(III), and Mn(III) (27,28,138). Thus, the introduction of these metals into the acetylacetone molecule results in a decrease in its thermal stability. The thermal stability of polymeric chelates [37] prepared from tetraacetylethane have been studied by therraogravimetry in argon at atmospheric pressure (25,26). 

The well-known thermal stability of most minerals and glasses, many of which are themselves polymeric, has led to intensive research into synthetic inorganic and semi-inorganic polymers. These materials can be classified into the following groups ... 

The corresponding polyiminocarbonates (Figure 5) were prepared first, using recently developed polymerization procedures (5). Poly(Dat-Tym iminocarbonate), the polymer carrying no pendent chains at all, was an insoluble material. Thermal processing techniques could not be used due to the low thermal stability of the polymer in the molten state. Thus poly(Dat-Tyr iminocarbonate) was a virtually non-processible material without practical applications. 

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