Isothermal weight loss

While the rate of decomposition in air was more rapid than in nitrogen, the kinetics of oxidative decomposition cannot be estimated reliably by isothermal weight loss because ofthe possibility of competing oxidative weight gain process. For this reason the kinetics were not estimated from the available data... 

Fig. 19. Structures of the bisbenzocyclobutene 41, the diacetylenes 42, 43 and the hismaleimide 44 used in the DSC and isothermal weight loss experiments described in Figs. 20-24...

The enhancement of thermal stability as measured by these isothermal aging experiments by the addition of bisbenzocyclobutenes to dienophilic thermosetting monomers has also been observed with bis activated acetylenes and dicyanates. The isothermal weight loss results obtained on a one to one mole... 

Via DSC measurements it was shown that the new bis(vinylbenzyl)ethers can undergo a homopolymerization and a copolymerisation with BMI. In a BMI/-divinylbenzylether blend the Diels-Alder copolymerization is favoured over the divinylbenzylether homopolymerisation. The Tgs of the new copolymers are well in excess of 270 °C when the BMI/divinylbenzylether molar ratio is 1 1 (Table 9). Isothermal weight loss studies over a period of 4000 hours indicate that the BMI-MDA/divinylbenzylether copolymer is the most stable system of this family. 

The curves of isothermal weight loss at 260°C for chloroparaffin/polymer mixtures show that the polymers are thermally destabilized by the presence of chloroparaffin, the destabilization increases in the sequence polyethylene, polypropylene, and polystyrene chain scission is induced in polypropylene and polystyrene whereas cross-linking is promoted in polyethylene, as shown in Table 4.3.35 At the same time, the rate of elimination of HCI from chloroparaffin is decreased by the presence of the three polymers. 

Figure 8. Isothermal weight loss of fully cured thermoset derived from BCB-2 monomer with time at 350°C in air.

High thermal and oxidative stability of the imide-linked fluorocarbon ether polymers is shown by thermogravimetric analysis in air (Figure 2). The weight loss was less than 5% to a temperature of 450°C. Isothermal weight loss in air at 260°C was less than 0.3% in 112 hours for the polymer where x + y = 3. 

Another type of argument to support a free radical mechanism was advanced by Palma and Carenza [172]. Thermal and 7-initiated dehydrochlorination between 80 and 130°C were compared. In view of the resemblance shown by the kinetic data for polyene formation, the same mechanism was thought to be operative in both cases. Since according to the authors, a free radical mechanism is clearly established for 7-initiated processes, this is also operative in thermal degradation. Salovey and Bair [171] reported that the thermal degradation of PVC at 155°C is enhanced by irradiation with 1 MeV electrons. Since later stages of isothermal weight loss for thermal and radiolytic decomposition follow 3/2 order kinetics, a free radical mechanism is also postulated by these workers. 

ACRYLIC 1 copolymer was cured at 3 J/sq-cm. The glass transition temperature was -42° C (under Nitrogen) and the isothermal weight loss after 1 hr at 200°C in air was 31%. 

Figure 22-10. Isothermal weight loss, type HN film, 0.025 mm.[ ...

Figure 2.15 Isothermal weight loss in H O/air at ZOO C for BN specimens with d 002) from 3.33 A to 3.67 A.

FIG. 13 Isothermal weight loss by PBI and phosphoric acid treated PBI in air at 500°C for 3 hours. 

The thermal stability of several commercial silanes was studied by determining isothermal weight loss of the hydrolyzed silsequioxane form of the silanes (RSiOj ) at 300°C [11]. Fig. 25.5 shows that the phenylsilyl structure has very good thermal stability, but that the diaminosilane has poorer thermal stability. The vinylbenzylaminosilane has surprising good thermal stability. Phenyltrimethoxysilane blends or vinylbenzylaminosilane have been recommended for high-temperature applications. 

Figure 3.7 Isothermal weight loss curves produced by thermo-oxidation in a forced air oven. Stoichiometric thermoset resin number 4 from diglycidyl ether of bisphenol A and we i3-phenylene diamine aged at four temperatures between 200 °C and 300 °C. Reproduced with permission from T. Dyakonov, RJ. Mann, Y. Chen and W.XK Stevenson, Polymer Degradation and Stability, 1996, 54,1, 67.

Isothermal weight loss for xerogels prepared by two-step acid-base-catalyzed hydrolysis of TEOS (r = 3.8) [61],... 

Gallo et al. [141] have shown that weight loss above 400°C is completely accounted for by water, the by-product of condensation. Therefore the kinetics of the condensation reaction may be monitored by isothermal weight loss experiments. Isothermal weight loss for the two-step acid-base-catalyzed silicate system is shown in Fig. 38. At 350 C weight loss varies approximately... 

Fig. 1. Isothermal weight loss for 51-n quartz + GE II CaCOs reacted in dry CO2.

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