Thermal stability measurements

Improved heat-resistant UV compositions for optical fiber applications These compositions are nonurethane UV cure compositions that have neither carbamate moieties nor long-chain poly(alkylene oxide) soft segments and exhibit inherently better thermal stability measured by thermogravimetric analysis (TGA) than typical coatings for optical fibers based on urethane acrylate oligomers. 

Outdoor exposure of these hlgh-denslty samples for the last 18 years caused no substantial change due to surface oxidation. Bulk changes similar to those found In low-density polyethylene were also found In these high density materials. The melt Index slowly decreases and the overall thermal stability measured at high temperature by thermal analysis decreases. However, the secondary crystallization seen In low-density polyethylene was not detected In these high density compounds. 

The polymers were synthesized by the standard NMP/K2CO3 procedure according to literature (10,11). Glass transition temperatures and thermal stability measurements (TGA) were performed on a Du Pont DSC 1090 instrument at heating rates of 10 and 5°C/min, respectively. Intrinsic viscosity measurements were determined using a Cannon- Ubbelhodhe dilation viscometer in NMP (25°C). 

An intriguing phenomenon was observed, when the purified bovine erythrocyte Cu ZnjSuperoxide dismutases, obtained by the different isolation techniques were compared. Thermal stability measurements revealed that the purified SOD s are much less heat resistant compared to the enzymes in the homogenates. Therefore, heat deterioration of the isolated protein must not be connected with the isolation technique described in Chapter 2.3. When freshly aqueously isolated Cu ZnjSuper-oxide dismutase was heated to 77 C a transient and marked increase of the specific enzymic activity is seen. 

The molecular hydrides, formed by nonmetals and metalloids, are either gases or liquids under standard conditions. The simple molecular hydrides are listed in FIGURE 22.6, together with their standard free energies of formation, AGf. (Section 19.5) In each family the thermal stability (measured as AGf) decreases as we move down the family. (Recall that the more stable a compound is with respect to its elements under standard conditions, the more negative AGf is.)... 

Petit and Neel [33] carried out thermal stability measurement on copolymers of cis and trans penta-1,3 diene and acrylonitrile. 

Liu and co-workers [7] have carried out thermal stability measurements on ladderlike polysilsesquioxones. These had a considerably higher thermal stability than the corresponding single, main chain polymers. 

Ziatinov and co-workers [9] synthesised poly(sila alkylene siloxanes) of 2,2,5,5 tetramethyl-l-oxa-2,5 -disilacyclopentane and carried out thermal stability measurement by TGA. 2,2,5,5- Tetramethyl-l-oxa-2,5-disilacyclopentane was shown to be quite stable at temperatures up to 315 °C in nitrogen. At higher temperatures, however, the polymer undergoes catastrophic decomposition and by 515 °C virtually no polymer is left. On the other hand, in air decomposition begins at 190 °C only 20% of the initial sample weight remaining at 350 °C and 15% at 800 °C. 

For the wholly aromatic TLCPs derived from TA, phenyl hydroquinone, and 3,4 -dicarboxyl phenylether [59], the thermal stability measured by TGA slightly decreases with the increasing ether content. All polymers exhibit good thermal stability up to about 400°C in N2 and 25°C lower in air, with a 20°C min heating rate. The thermal stability of the TLCPs decreases when the phenyl hydroquinone is replaced by (1-phenylethyl) hydroquinone. 

There are other methods that predict reactivity more reliably than the oxygen balance method. These methods, however, require the use of data generated by measurements. Stull devised a relatively simple Reaction Hazard Index or RHI that used both kinetic and thermodynamic data measurements. This index is a graphic model (nomagraph) that uses the Arrhenius activation energy and the decomposition temperature The latter term is the maximum adiabatic temperature reached by the products of a decomposition reaction. If data are available or can be measured, the RHI may be a very useful method to predict reactivity. Coffee described a method that predicts the explosive potential of a compound using thermal stability (measured), impact sensitivity (measured), and the heat of reaction (calculated). Compounds found to be thermally unstable and sensitive to impact were explosive. 

To look for possible relations of thermal stabilization, measured as increase in Td, to other parameters of the proteinase—inhibitor interaction, we plotted increases in Td of the proteinases resulting from their association with the inhibitors as a function of the logarithms of the equilibrium association constants (log Kai or). Published values of Kgssoc vary somewhat (see Zahniey, 1980, W references to values used), and these values were not determined under the same conditions as used for the DSC experiments. Accordingly, ranges of log Kgssoc vere used in Figure 8. Values fell within a narrow... 

Recent work has been performed, which shows that TG can be used to demonstrate change in the thermo-oxidative stability of HDPE due to oven ageing. A variety of ASTM test methods for heat ageing and thermal stability measurements are based on the use of TGA e.g. D 1870, D 2126, D 3045, D 4202, D 5510 and E 1641). 

Thermal stability measurements have been carried out on numerous other polymers including polyethylene ethylene vinyl-alcohol copolymer [12], polyaniline [13], ) 3 s-stilbene-N-substituted maleimides [14], cellulose [15-20], polystyrene [14, 16], ethylene-styrene copolymers [21,22], ST-DVB-based ion exchangers [23], vinyl chloride-acrylonitrile copolymers [24], polyethylene terephthalate [25], polyesters such as polyisopropylene carboxylate [26], polyglycollate [27-29], Nylon 6 [30], polypyromellitimides, poly-N-a-naphthylmaleimides [26,31], polybenzo-bis(amino-imino pyrolenes) [32], polyvinyl chloride [33-35], acrylamide-acrylate copolymers and polyacrylic anhydride [36-38], polyamides [39], amine-based polybenzo-oxazines [40], polyester hydrazides [41], poly-a-methyl styrene tricarbonyl chromimn [42], polytetrahydrofuran [43], polyhexylisocyanate [44], polyurethanes [45], ethylene-... 

Thermal stability measurements on Ti-5A1-2.5Sn made by comparing room-temperature properties before and after thermal exposiure (stressed or unstressed) have indicated that this alloy is metallurgically stable under any conditions of stress, temperature, and time up to the an-... 

Fig. 5.22 (a) The electrochemical features of Li]+ (NMC)i j.-Coi/302 powders synthesized by the co-precipitation method. The structure was optimized by adjusting the lithium-transition metal ratio to k = 1aJM = 1.05. Results indicated a rate of 0.15 % per cycle for the NMC electrodes, (b) Diagram discharge capacity against thermal stability measured by the exothermic peak temperature for a series of LiNij..MnyCoj,02 cathode materials. The number indicates the amount of Ni/Mn/Co... 

Electrodeposited Au-Cu alloys Structural analysis, thermal stability measurements and mechanical characterization, L. Battezzati, M. Baricco, S. Barhero, A. Zambon, I. Calliari, A. Variola, B. Bozzini, P. L. Cavallotti, G. Giovannelli, and S. Ti r taE, La metallurgia italiana 93(2) (2001) 17. (In Italian)... 

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