Neat PTFE

Aromatic polyimides are well known for their unusual array of favorable physical properties, including excellent thermal stability and excimer-laser processing characteristics. The polyimide structure possesses lower-energy transitions such as n — Jt, n c, Jt — Jt, and o — k (in order of increasing energy ). However, the n — Jt and o — Jt transitions are forbidden by symmetry rules and related absorptions are significantly weaker than those for 

PTFE is commercially available in three forms (1) skived films (2) powder and (3) aqueous dispersions. Of the three forms, the aqueous dispersion provides the most suitable medium to approach a level of mixing and uniformity of the host matrix and dopant that is achieved when transparent matrices and sensitizers share 

The initial and primary decomposition product for BPDA-PDA is a negative ion fragment with m/z = 229. The chemical structure associated with the 229 ion has not yet been assigned. Product-formation by pyrolysis decomposition of 

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Figure 5.10 is the dynamic TGA scan of neat PTFE in air and N2. Under each atmosphere studied, it is readily apparent that the onset of degradation occurs at about 500°C. TGA data are also in excellent agreement with a more sensitive and structurally informative pyrolysis/mass spectroscopy analysis. Figure 5.11 is a... 

Figure 5.10. Dynamic TGA scans of neat PTFE in air (-) and N2 (----) atmospheres (from...

Figure 5.11. Dynamic pyrolysis/FTMS scan of neat PTFE (from Davis and Zimmerman74).

The threshold fluence decreases with increasing dopant concentration and for the lowest concentration where ablation is observed (0.2% polyimide) the threshold fluence is about 0.7 J/cm2 at 248 nm and about 0.9 J/cm2 at 308 nm. Additionally, at fluences around 10 J/cm2, the maximum measured etching rates at 248 and 308 nm are about 3 and 6 pm/pulsc, respectively. While the etching rate for the 248 nm ablation of the 0.2% polyimide-doped sample has begun to saturate, the corresponding curve for the 308-nm ablation is still increasing. In comparison, the threshold fluence for the ablation of neat PTFE using 300 fs... 

Figure 4.89. (a) Neat PTFE creep examples of creep modulus (GPa) versus time (h) for loading from 3.5 up to 7 MPa ... 

Neat PTFE has several properties which eliminate its need for additives. A very high limiting oxygen index (>95%) means that resin is nonflammable. Its thermal and electric insulation properties and its low friction coefficient means that further improvements are rarely needed. An improvement in mechanical properties may sometimes be needed but this is usually obtained at the expense of chemical resistance because most fillers detract from the chemical resistance of neat PTFE. The addition of NiZn ferrite powder is used to impart ferromagnetic properties to the... 

Dopant-induced ablation is of great significance because it provides the opportunity to process materials that do not exhibit desirable excimer laser structuring characteristics, i.e., micro-feature formation, but offer other outstanding properties, e.g., low e,. Like the matrix polymers of the initial doping investigations, neat PTFE is transparent to conventional excimer laser emissions. FIFE, whose chemical repeat unit is... 

Figure 4. Absorption coefficients at 308 nm for polyimide/PTFE blends predicted using a rule of mixtures relationship for polyimide dopant concentrations (weight fraction of polyimide) up to 5.0%. Calculated values of a blend over the full range of polyimide concentrations, from neat PTFE to neat polyimide (Upilex-S film), are given in the inset.

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