Polyimide solution characterization

The synthesis of well-defined LCB polymers have progressed considerably beyond the original star polymers prepared by anionic polymerization between 1970 and 1980. Characterization of these new polymers has often been limited to NMR and SEC analysis. The physical properties of these polymers in dilute solution and in the bulk merit attention, especially in the case of completely new architectures such as the dendritic polymers. Many other branched polymers have been prepared, e.g. rigid polymers like nylon [123], polyimide [124] poly(aspartite) [125] and branched poly(thiophene) [126], There seems to be ample room for further development via the use of dendrimers and hyperbran-... 

The solution behavior of poly(amic acids) was until recently, probably the least understood aspect of the soluble polyimide precursor. However, the advent of sophisticated laser light scattering and size exclusion chromatography instrumentation has allowed elucidation of the solution behavior of poly(amic adds). In the early days of polyimide chemistry, when most molecular weight characterization was based on viscosity determinations, a decrease in viscosity was associated with molecular weight degradation [15, 28, 29]. Upon combination of the two monomers an increase in the viscosity to the stoichiometric equivalence point is observed, followed by a decrease in the solution viscosity as a... 

Adhesion of polyimides to inorganic substrates is of great importance to the microelectronics industry [1, 2]. The polyimide films are deposited most often by spin coating the polyamic acid (PAA) usually from a TV-methylpyrrolidone (NMP) solution onto the substrate surface followed by thermal imidization at temperatures up to 400<>C. The most studied polyimide is the pyromellitic dianhydride-oxydianiline (PMDA-ODA), which exhibits excellent mechanical and dielectric properties, but not so good adhesion characteristics. The latter has been generally overcome by application of an adhesion promoter, such as y-aminopropyltriethoxysilane [3-7]. The reactions of APS (coated from water solution) with the silicon dioxide surface as well as with polyamic acid have been well characterized by Linde and Gleason [4] however, we do not have such detailed information available on APS interaction with other ceramic surfaces. 

The substrates used in this study were (0001) sapphire (A1203), (001) magnesia (MgO), and amorphous fused silica (Si02). All substrates were obtained with surface finish to 0.025 / m, and were cleaned with isopropylalcohol (IPA) prior to PA A or APS application. The surfaces and interfaces after peel test were characterized using X-ray photoelectron spectroscopy (XPS). The PMDA-ODA PAA was cast from NMP solution. Figure l shows the structure of the PAA and the thermally imidized PMDA-ODA polyimide. 

Synthesis of Siloxane-Polyimide Thermoplastics. In a typical siloxane-polyimide thermoplastic preparation, a 2-L, three-neck flask equipped with an overhead mechanical stirrer, Dean-Stark trap with condenser and nitrogen inlet, and a thermometer was charged with 106.41 g (0.230 mol) of DiSiAn, 119.71 g (0.230 mol) of BPADA, 49.74 g (0.460 mol) of mPD, 8.55 g (3 wt %) of 2-hydroxypyridine, and 635 mL of o-dichlorobenzene. The mixture was warmed to 100 °C for 1 h to dissolve the monomers and catalyst. Polyamic acids precipitated and redissolved when the mixture was heated to 150 °C for 1 h. The solution was then warmed to reflux, and 15 mL of water of reaction was removed by azeotropic distillation. The mixture was maintained at 180 °C for 16 h. The solution became noticeably more viscous. The polymer was isolated and purified as described previously to obtain 232 g (90%) of polymer with an IV of 0.54 dL/g. The isolated polymer was characterized spectroscopically. DSC indicated a Tg (glass transition temperature) of 196 °C. 

The chemical structure of the polyimide polymers (named PI-1 and PI-2) studied by Sekkat et al. is shown in Figure 12.12. They prepared the polymer samples by spin-casting onto glass substrates. PTl was cast from a cyclohexanone solution and PI-2 from 1,1,2,2- tetrachloroethane. The Tg values of PI-1 and PI-2 were determined to be 350°C and 252 C, respectively, by scanning calorimetry method. The thicknesses of the PI-1 and PI-2 films were, respectively, approximately 0.72 im and 0.14 im, and their respective optical densities were approximately 0.79 and 0.3 at 543.5 nm. Details of the preparation and characterization of the samples can be found in References 3 and 20. In their EFISH experiment, a typical corona poling technique was used to pole the samples, with a dc electric field about 2-3 MV/cm across a 1-2 lm thick polymer film. They used the SHG output from the EFISH experiment to in situ monitor the photochemical change in the third-order susceptibility of the PI-1 and PI-2 polymers. 

In this article, the synthesis, characterization, rheology, solution processing, and mechanical properties of novel molecular composites are discussed. These molecular composite are block copolymers composed of a liquid-crystalline polyamide and two amorphous polyimides. Also, the rheological properties of both isotorpic and anisotropic solutions of PBTA homopolymers and PBTA/PI block copolymers are... 

Rohit H. Vora, P. Santhana Gopala Krishnan, S. Veeramani and Suat Hong Goh (2003) Poly(amic acid)s and their ionic salt solutions S)mthesis, characterization and stability study. In Polyimides and Other High Temperature Pol3nners, Vol. 2. K.L. Mittal editor. VSP. pp. 14-35. 

HOU Hourdet, D., Muller, G., Vincent, J.C., Avrillon, R., and Robert, E., Characterization of polyimides in solution. Relation with the preparation of asymmetric membranes, in Polyimides and other High-Temperature Polymers, Elsevier Sci. Publ., Amsterdam, 507, 1991. 

Most of those systems were using (thin film) Ag/AgCl elements, which are not free from problems in manufacturing (e.g. related to poor adhesion of silver to glass/silicone) leading to poor potential stability [8]. Improvements proposed [8] included application of intermediate polyimide layer instead of previously applied metal ones and special formation of AgCl layer on top of silver film. Thus obtained sensors were characterized with increased stability of potentials in KCl (up to 8 h) as well as in interferent (KI or K2S) solutions [8]. 

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