Simultaneous TGA/DTA Experiments

Data for the uncatalyzed polycondensation from STA (simultaneous TGA/DTA) experiments under high-flow inert gas at atmospheric pressure [8] are shown in Figure 2.28. These data also demonstrate the dependency of the overall polycondensation rate on the polymer film thickness. 

Kinetics according to ASTM E 698-79 from simultaneous TGA/DTA experiments... 

Software only for the Simultaneous Thermal Analyzer STA 780 was available for kinetics according to Borchardt and Daniels. Similarly to the kinetics program according to ASTM E 698-79, only separately sampled DTA data can be processed using the Borchardt and Daniels program. The DTA data from simultaneous TGA/DTA experiments cannot be... 

Thermal gravimetric analysis and differential thermal analysis (TGA/DTA) can be performed by using a SDT 2960 Simultaneous Differential Thermal Analyzer (TA Instruments, Inc., New Castle, DE). The instrument was calibrated with gold supplied by Perkin-Ehner. Samples (70 mg) of as-prepared powders were hand-pressed in a 3 mm dual action die and placed inside Pt sample cups and heated at the rates of 10 K/ min from ambient temperature to 1400°C. The reference material was used as a pellet of a-alumina. A flow of synthetic air at 50mL/min was maintained during the experiments. 

Some of the simultaneous instruments available commercially are as follows TGA/DTA/DSC, TGADTA/FTIR, DTA(DSC)/EGA(EGD), and DSC/FTIR. Also, high pressure DSC and photo-DSC instruments are available commercially. In addition, individual researchers have used simultaneous DSC/XRD (X-ray diffraction), DSC/EGA/XRD, and DSC/TRXRD (time-resolved X-ray diffraction). Experiments with parallel, combined, and simultaneous techniques help to affirm the conclusions drawn from a single technique and very often offer definitive clues to the actual mechanisms taking place during thermal analysis. 

Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) experiments were performed in a simultaneous DTA-TGA apparatus (Shimadzu DTG 60). Throughout the experiment, the sample temperature and weight-heat flow changes were continuously monitored. The conditions of measurement were heat flow 10 °C/ min and dynamic atmosphere of nitrogen (50 ml/min). The range of temperature measurement was from 40 to 500 °C. 

Simultaneous Thermal Analysis (STA) A technique which combines DTA, TGA, DSC (cal.) and derivatives of DTA/TGA in a single instrument, offers advantages over the performance of each technique as a separate experiment on stand-alone instruments. By examining a single sample, one ensures no variation in sample homogeneity, atmosphere difference and other instrumental parameters. At the same time, there is a provision for detection and analysis of evolved gases (EGA) during thermal decomposition. Also, derivatives of TGA and DTA can be precisely measured (electronically). 

Figures 4.179 and 4.180 illustrate two furnaces for TGA for different temperature ranges. The figures are self-explanatory. Several different sample holders are shown in the bottom portions of the figures. The multiple holders can be used for simultaneous thermogravimetry and DTA, the single cmcibles are used for simple thermogravimetry. The major problem for the combined thermogravimetry and DTA technique is to bring the thermocouple wires out of the balance without interference with the weighing process. Even the temperature control of the sample holder may be a major problem in vacuum experiments since the thermocouple does not touch the sample. The cmcibles are made of platinum or sintered aluminum oxide. Typical sample masses may vary from a few to several hundred milUgrams.

The synthesis of 1,2, and 3 have been reported previously. All reactions were carried out in an inert atmosphere unless otherwise noted. Solvents were purified by established procedures. 1,3-Dichlorotetramethyldisiloxane and 1,5-dichlorohexamethyltrisiloxane were obtained from Silar Laboratories and used as received. -Butyllithium (2.5 M in hexane) was obtained from Aldrich and used as received. l,7-Bis(chlorotetra-methyldisiloxyl)-/w-carborane 1 was purchased from Dexsil Corporation. Hexachlorobutadiene was obtained from Aldrich and distilled before use. Cure and thermal analysis studies were performed on various mixtures of 1 and 3a in milligram quantities. Thermogravimetric analyses (TGA) were performed on a DuPont SDT 2960 Simultaneous DTA-TGA analyzer. Differential scanning calorimetry analyses (DSC) were performed on a DuPont 910 instrument. Unless otherwise noted, all thermal experiments were carried out at a heating rate of 10 °C/min and a nitrogen flow rate of 50 cc/min. 

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