Polyimides prediction

Polyimide Predicted Predicted Experimental Diff % Diff. 

Polyimide Predicted dielectric constant Experimental dielectric constant ((si kHz) Diff. % Diff. 

However, fluorocarbon compounds might be of considerable interest for LB-layer fabrication. Their dielectric and mechanical characteristics and thermal and chemical stability are not inferior to those of polyimides, and highly developed synthesis technology makes it possible to create systems with various predictable properties. Such films have been found to demonstrate a high degree of perfection and excellent dielectric characteristics.69,70... 

Figure 5.18. Absorption coefficient at 308 nm for PI-PTFE blends predicted using a rule-of-mixtures relationship for polyimide dopant concentrations (weight fraction of polyimide) up to 15%. Calculated values of the absorption coefficient over the full range of polyimide concentrations from PTFE to polyimide are given in the inset (from Egitto and Davis57).

The tangent of the capacitance phase angle has been shown to be a measure of the completeness of the anneal (2.) Based on this technique, we have data which would predict 30 minutes at 300°C is sufficient to obtain optimum dielectric properties. However, we have found chronogravimetric analysis of polyimide films to be more useful in defining optimum anneal conditions. 

The effective bulk polyimide resistivity can be extracted from comparison of the measured curves in Figure 6 with this model, and values at 100°C and 158°C are shown in Figure 7, which is a reproduction of the Arrhenius plots of Figure 4. It is seen that both the values of the resistivity and the temperature dependence are in good agreement with those obtained from the dc conduction measurements. In addition, the saturated value of the measured threshold instability is well predicted by the model. 

Recently, a series of hexafluoro-isopropylidene-containing polyimides have become available, providing an opportunity to investigate the miscibility of pairs of closely related polyimides. The miscibility criteria of these fluoro-polyimides with one another and the use of the Flory-Huggins theory to predict the miscibility in these systems will be summarized. 

Predicted and measured values of PI-PTFE blend dielectric constants (g ) versus polyimide. 

The chapter is divided into the following sections. First, a brief introduction to group contribution methods is given with a major emphasis on the concept and limitations of this technique. An introduction to the use of chemical graph theory and how it applies to polymers and in particular to the dielectric constant is given next. Application of the method to a number of polyimides is then demonstrated and predictions are compared to experimental results. 

Figure 12.1 shows how well the predicted results agree with the experimental values listed in Table 12.2. The predictions consistently overestimate experimental dielectric constant values for this series of samples. The difference varies from 12 to 27% of the experimental values. Qualitatively, predictions follow the same trend as experiment. The calculated slope for the best straight-line fit through the data points is equal to 0.822 with a standard deviation of 0.088. The correlation coefficient is equal to 0.881. For several of the polyimides tested here the method... 

Figure 12.1. Comparison of predicted dielectric constants to experimental dielectric constants for a series of dry polyimide samples measured at a frequency of 10 MHz.

Figure 12.2 shows the results of comparisons between prediction and experiment for the polyimides listed in Table 12.3. The correlation coefficient is determined to be 0.767. Its value can be improved to 0.957 by not considering the polyimide whose predicted dielectric constant value is equal to 3.02. The slope of the best-fit line is equal to 0.737, with a standard deviation of 0.232. 

Recently, the same series of six polyimides was studied by positron annihilation spectroscopy to determine die fractional free volume directly. In all three H/F analogue pairs, the increased free volume of the fluorinated polymer accounted for around 50% of the observed decrease in refractive index and dielectric constant. This result confims an astonishingly large free volume contribution predicted by our earlier estimates.Future work will investigate the generality of this result to other polymer systems. 

Alentiev, A. Yu., Loza, K. A., and Yampol skii, Y. P. (2000). Development of methods for prediction of gas permeation parameters of glassy polymers Polyimides as altenating copolymers, J. Membrane Sci. 167, 91. 

Figure 5. HREELS cross-section curves (peak height normalized to the elastic peak intensity) for the excitation of selected molecular vibrational bands of polyimide. The dielectric theory predicts a E 1 behaviour.

In order make an effort to bring the polyimide-metal adhesion problem to an even more fundamental level, we have previously proposed that model molecules, chosen as representative of selected parts of the polyimide repeat unit, may be used to predict the chemical and electronic structure of interfaces between polyimides and metals (12). Relatively small model molecules can be vapor deposited in situ under UHV conditions to form monolayer films upon atomically clean metal substrates, and detailed information about chemical bonding, charge transfer and molecular orientation can be determined, and even site-specific interactions may be recognized. The result of such studies can also be expected to be relevant in comparison with the results of studies of metal-polymer interfaces. Another very important advantage with this model molecule approach is the possibility to apply a more reliable theoretical analysis to the data, which is very difficult when studying complex polymers such as polyimide. 

For the cured polyimide, the CF /F ratio was calculated using the integrated peak area results. A value of 0.33 was determined experimentally (vs. the value of 0.33 predicted). Extensions of this approach occurred by calculation of =C=0/N and =C=0/ ratios. Values of 1.08 and 0.32, respectively, were determined experimentally (vs. 2.0 and 0.67 predicted on the basis of structural formula considerations). These results indicated either carbonyl deficiency, an excess of nitrogen or an excess of fluorine in the surface region. 

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