Polyimides thermogravimetric analysis

The process known as transimidization has been employed to functionalize polyimide oligomers, which were subsequentiy used to produce polyimide—titania hybrids (59). This technique resulted in the successhil synthesis of transparent hybrids composed of 18, 37, and 54% titania. The effect of metal alkoxide quantity, as well as the oligomer molecular weight and cure temperature, were evaluated using differential scanning calorimetry (dsc), thermogravimetric analysis (tga) and saxs. 

All the polyimides are thermostable. They do not melt before decomposition at high temperature. In thermogravimetric analysis, the decomposition starts at more than 400°C. 

Thermogravimetric analysis, though not necessarily indicative of all high temperature properties, is a convenient way to indicate the degree of thermal reaction occurring at a particular temperature. The thermal stability of polyimides has been the subject of many studies (10). Our results obtained from free films of 1-2 mils are shown in Fig. VII and are in agreement with Heacock and Berr(ll). Since 1-2 mil films are not used here, we decided to study the thermal degradation of... 

The primary thermal characteristics of the polyimides were determined by dynamic thermogravimetric analysis (TGA) as well as thermomechanically. Although the data for dynamic TGA should be treated with some reservation, one can conclude the following ... 

Examination of the thermal stability of the polyimides synthesised, carried out using differential thermogravimetric analysis (air, AT = 4.5 °C/min), revealed that, under the conditions specified, the 10% weight loss (used as a criterion of thermal stability) is almost independent of the structure of the polyimides (Table 5.1). For all polyimides examined, the 10% weight loss temperature was 400 °C. The relatively low thermal stability of these polyimides may be related to the presence of the methoxy groups. 

The glass transition temperatures ofthe polyimides are 195-250 °C their 10% weight loss temperamres (dynamic thermogravimetric analysis, air, AT = 4.5 °C/min) are 390-422 °C. Of particular interest are the dielectric constants of these polyimides. At a relative humidity of 50% these constants are 2.70-2.90 and are comparable with constants of the best fluorinated polyimides [21, 50-55]. The lowest dielectric constant (2.70) was observed for polyimide based on 6F dianhydride, containing the highest amount of fluorine. Thermal treatment of this polymer film at 280-290 °C for 1 hour led to a decrease (2.45) of dielectric constant due to the possible formation of nanofoams [56]. 

The requirement of a controllable level of charged groups having been met, attention turned to the elimination of the amine modifier. In order to obtain the desirable properties of the polyimide, it was important that the modification be readily eliminated. At the outset, there was an indication in the literature that this would in fact be the case. In 1970, Delvigs and co-workers (I 3) reported the diethylamide derivative of a polyamic acid as an alternative precursor to polyimides. They provided IR evidence that the amine was eliminated thermally to form a polyimide indistinguishable from that obtained from the polyamic acid. In the present work, the elimination of 1-methylpiperazine was followed by thermogravimetric analysis (TGA), IR, and size exclusion chromatography (SEC). 

General. Commercially available polyimides were used (see Table I). Solvents were reagent grade or better and were used as received. 1-Methylpiperazine (Aldrich Chemical Co.) was > 99.9% pure. Lactic acid (Aldrich) was reduced to 50% by weight in water and refluxed for an hour to hydrolyze esters. IR spectra were recorded on a Perkin-Elmer Model 1430 spectrometer. Thermogravimetric analysis was done on a P-E System 4/TGS-2 instrument. Size exclusion chromatography was done on a Perkin-Elmer Series 3B equipped with the LC-75 spectrophotometric detector. The column set used consisted of P-E 0258-2134, 2133, and 2131 columns (pore sizes 103, 104, and 106 A, respectively). For electrophoretic deposition experiments, a TCR Power Supply (Electronic Measurement Systems Inc.) was used. Temperatures are reported in °C throughout. 

Figure 2. Thermogravimetric analysis of polyimides, heating rate 30°C/min.

Thermal stabilities of the polyimides were examined by Thermogravimetric Analysis. The integral procedural decomposition temperature (IPDT), a semi quantitative method, has been used to evaluate the relative thermal stabilities of the PT and MT series. The results are listed in Table 3. 

Three carbon fibre-reinforced polyimides were exposed to UV radiation at 177C, at three different intensities for three different times, so that the product of intensity and time was a constant. Intensities of 1,2 and 3 suns, where one sun is the power in space at one earth-sun distance, were used, for a time periods of 500, 250 and 167 h. The samples were characterised by X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, thermomechanical analysis and dynamic mechanical analysis. Measurement of bulk properties showed no difference between samples exposed to heat and UV radiation, and control samples. Surface analysis by XPS showed an apparent decrease in carbonyl concentration on the surface of some exposed samples. This was correlated to surface contamination by a silicone-containing material. 3 refs. 

Thermogravimetric analyzers may be connected to a variety of chemical analyzers to determine the exact composition ofthe outgassed materials as they are evolved. Among chemical analysis methods are gas chromatography, infrared spectroscopy, and mass spectroscopy for example, a TGA apparatus may be coupled with a Fourier Transform Infrared (FTIR) spectrophotometer to measure the thermal oxidative stabilities of several fluorinated polyimides. 

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