Polyimide repeat unit

As an approach to a better understanding of adhesion mechanisms between polyimide and copper, we have studied the interaction between a set of model molecules for a polyimide and vapor deposited polycrystalline copper. Thin films and adsorbates of benzene, phthalimide, methyl-phthalimide, benzene-phthalimide, and malonamid, which are representative of separate parts of the polyimide repeat unit, were deposited in situ on clean copper and examined by means of X-ray and Ultraviolet photoelectron spectroscopy (XPS and UPS). In contrast to the previously observed bonding to the carbonyl oxygen in polyimide, as Cu is deposited on polyimide, our results show that most of these polyimide model molecules bond to Cu, through electron transfer, with the imide nitrogen atom as the primary reaction site. 

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. 

From a semi-quantitative analysis as described elsewhere [6] we obtain an 0 N C ratio of 4.7 2.6 22 compared with the stochiometric ratio of 7 2 22 (normalized to 22 carbon atoms per polyamic acid (or polyimide) repeat unit). Considering the contributions of the ODA and the PMDA monomers to the nitrogen to carbon (N C) ratio the composition of the polyamic acid can be calculated independent of the degree of imidization. Using this method we obtain a monomer distribution of 66% ODA to 34% PMDA compared with a 50% to 50% distribution expected for stochiometric... 

Fig. 24. Numbering of the earbon and oxygen atoms in the repeat unit of PMDA/ODA polyimide. Reprodueed by permission of John Wiley and Sons from Ref. [33].

Nylon, polyacetal, polycarbonates, poly(2,6-dimethyl)phenylene oxide (PPO), polyimides, polyphenylene sulfide (PPS), polyphenylene sulfones, polyaryl sulfones, polyalkylene phthalates, and polyarylether ketones (PEEK) are stiff high-melting polymers which are classified as engineering plastics. The formulas for the repeating units of some of these engineering plastics are shown in Figure 1.15. 

Aromatic polyimides have the following repeating unit ... 

New heterocyclic polymers designed especially for service at elevated temperatures have intriguing properties, some of which are in contrast to properties usually associated with linear noncrystalline polymers. These polymers have sometimes been described as stiff chains because of the long inflexible repeat units of which they are comprised. Relatively few quantitative studies have yet appeared in the dilute solution properties or the viscoelastic behavior of the new heterocyclic polymers—partly because of the difficulties inherent in working with the poorly soluble materials. Some studies on the polyimide with the (idealized) structure ... 

Hao, J. J., Jikei, M., and Kakimoto, M.A. 2003. Synthesis of hyperbranched aromatic polyimides having the same repeating unit by AB2 self-polymerization and A2 + B3 polymerization. Macromolecules, 36, 3519-3528. 

Figure 10.5 Development of the H-bond network in a sulfonated polyimide (homo)polymer made of chains of aromatic and polyaromatic substituted cycles. Three repeat units of a chain are represented. Structure of the dried membrane in the upper drawing, of the membrane in equilibrium with an atmosphere with hygrometry 15% (middle page drawing) and 65% (lower drawing).

Ab initio molecular orbital calculations have played a central role in the analysis and interpretation of X-ray photoemission data obtained on the PMDA-ODA polyimide surface 1 4. The repeat unit of the PMDA-ODA polyimide is shown in Figure 1 and is constructed from planar pyromellitimide (PMDA) and diphenyl ether segments. An understanding of the XPS data and its relationship to the surface chemistry prior to the deposition of any metal is crucial with respect to the interpretation of changes in the XPS data which signify important metal-polymer chemistry that occurs upon formation of the interface. 

Dolden et al. [43] successfully synthesised a thermotropic polyetherimide from biphenylene dianhydride and l,12-bis(4-aminophenoxy) dodecane. This polyimide was mobile in the melt at 300 °C and exhibited a highly viscous anisotropic phase. Several LC oligoimides were also synthesised by the same workers who showed that more than two aromatic rings per repeat unit seem to be required in order for anisotropic behaviour to be observed. 

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