Polyimide dependence

The optical loss of polyimides depends on their preparation conditions. Reuter et al. have reported the optical loss of commercial fluorinated polyimides in waveguide materials containing two-C(CF3)2- groups, 6FDA/3,3 -6F or 6FDA/4,4 -6F, and estimated the optical loss to be below 0.1 dB/cm at 0.63 pm using optimized conditions. However, the loss increases to around 3 dB/cm with a... 

Hara et al. (1985) measured mobilities of pyrolyzed films of poly(N,N -/ , //-oxydiphenylene pyromellitimide) (polyimide). The properties of polyimides are known to be strongly dependent upon the pyrolysis temperature. Both electrons and holes are mobile in polyimide. Depending on the pyrolysis temperature, the mobilities were in the range of 10-7 to 10-3 cm2/Vs. 

Polyimides are step-ladder polymers, i.e. they have single-strand and double-strand linkages. Hie polymer chains are only as strong as their weakest link, and hence it is the single strand, i.e. the diamine, which limits the performance of the pyromellitimides. Hie softening point of the polyimide depends on chain flexibility which is inversely dependent on chain length. At least nine carbon atoms appear to be required for the resultant polyimide to be mouldable belew its decomposition temperature. Hie resultant polymers retain toughness for up to 25 hours in air at 175°C. 

Banerjee et al. [47] synthesized a diamine monomer, namely, 4,4 -(7w(aminophenoxy)-3,3-trifluoromethyl terphenyl, and furthermore prepared fluorinated polyimides (3-70 to 3-72 in Table 3.4). The Tg of the polyimides depended on the rigidity of the dianhydride unit. The polyimide with PMDA as dianhydride had the highest Tg of 294 °C in the series, with a thermal stability as high as 532 °C in an air atmosphere. The TS of the poly(ether imide) s were in the range 96-112 MPa with an EB in the... 

Overall, the general properties of polyimides are outstanding. However, it is best to keep in mind that polyimides, depending upon their chemical structures, have widely divergent properties, but overall, their ability to maintain structural integrity and good mechanical and electrical properties at elevated temperatures are the main reasons why polyimides are utilized today. 

Some requirements to use these polymers for interlayer and intermetal dielectrics in advanced microelectronic applications are high thermal stability, high glass transition temperature, good mechanical properties, low dielectric constant, low coefficient of thermal expansion and low moisture absorption. The dielectric constant of polyimides depends mainly on the... 

Amorphous Semi-crystalline (14%) Polyimide, depending on structure... 

The reactions of primary amines and maleic anhydride yield amic acids that can be dehydrated to imides, polyimides (qv), or isoimides depending on the reaction conditions (35—37). However, these products require multistep processes. Pathways with favorable economics are difficult to achieve. Amines and pyridines decompose maleic anhydride, often ia a violent reaction. Carbon dioxide [124-38-9] is a typical end product for this exothermic reaction (38). 

Since successful commercialization of Kapton by Du Pont Company in the 1960s (10), numerous compositions of polyimide and various new methods of syntheses have been described in the Hterature (1—5). A successful result for each method depends on the nature of the chemical components involved in the system, including monomers, intermediates, solvents, and the polyimide products, as well as on physical conditions during the synthesis. Properties such as monomer reactivity and solubiHty, and the glass-transition temperature,T, crystallinity, T, and melt viscosity of the polyimide products ultimately determine the effectiveness of each process. Accordingly, proper selection of synthetic method is often critical for preparation of polyimides of a given chemical composition. 

Cycloahphatic diamines react with dicarboxyUc acids or their chlorides, dianhydrides, diisocyanates and di- (or poly-)epoxides as comonomers to form high molecular weight polyamides, polyimides, polyureas, and epoxies. Polymer property dependence on diamine stmcture is greater in the linear amorphous thermoplastic polyamides and elastomeric polyureas than in the highly crosslinked thermo set epoxies (2—4). 

Methods of preparation of the laminates depend on the partieular grade of polyimide resin used but in one process the polyimide precursor is dissolved in acetone and this solution is used to impregnate the glass or carbon fibre and thus produce a pre-preg . The pre-preg is dried and then pre-cured at about 200°C for about 3 hours. This operation reduces the volatile content and also modifies the flow properties to make them more suitable for the subsequent... 

PI nanocomposites have been prepared by various methods with different fillers. The nanocomposites might have many applications starting from barrier and thermal resistance to a compound with low coefficient of thermal expansion (CTE) [154-167]. These hybrid materials show very high thermal and flame retardation as well as barrier resistance and adhesion. Tyan et al. [158] have shown that depending on the structure of the polyimide the properties vary. Chang et al. [159] have also investigated the dependency of the properties on the clay modifiers. 

FIG. 13 Reduction of the relative permeability coefficient is dependent on the clay platelet aspect ratio in the system of polyimide-clay hybrid with water vapor as the permeate. Each hybrid contains 2 wt% clay. The aspect ratios for hectorite, saponite, montmorillonite, and synthetic mica are 46, 165, 218, and 1230, respectively. (From Ref. 71.)... 

In 1977, Parshall and co-workers published their work on the separation of various homogeneous catalysts from reaction mixtures.[46] Homemade polyimide membranes, formed from a solution of polyamic acid were used. After reaction the mixture was subjected to reverse osmosis. Depending on the metal complex and the applied pressure, the permeate contained 4-40% of the original amount of metal. This publication was the beginning of research on unmodified or non-dendritic catalysts separated by commercial and homemade membranes. 

In figure 2 the dependence h(l]) is shown, from which follows rapid decrease h or increase of homogeneity of reactive medium at Tt raising. At 7 540 K exponent h=0, i.e., reactive medium becomes homogeneous. The authors [1] have show that the melting temperature Tm for studied polyimides is about equal to 800 K. On the basis of the known law of two-thirds... 

Davis et al. reported the successful etching of PTFE using single-photon energies in the quartz UV (308 nm and a pulse duration of 25 ns) by sensitizing the fluoropolymer with polyimide. 72 The number of pulses varied depending on fluence and material composition in order to achieve ablated features whose depths were reproducible as measured by a stylus-type profilometer. The pulse repetition rate was on the order of about 200 Hz. In that study, dopant levels... 

Estimates of oCbiend using a rule-of-mixtures relationship are 3.0 X 102 and 7.2 X 103 cm lor 0.2 and 5.0% polyimide, respectively. This dependence of the optimum absorption coefficient (in terms of ablation rate), OVx on fluence is consistent with the observations of Chuang et al.6% for ablation of several UV-transparent (at 308 nm) polymers sensitized with low-molecular-weight dopants, e.g., PMMA doped with pyrene. For the pyrene-PMMA system, Chuang et al.6S reported maximum etch rates for 1.2 J/cm2 at a = 7 X 102 cm 1. It should not be expected that different dopant-matrix systems would yield the same optimum absorption coefficient for a given fluence level since the thermal properties for different polymers may vary significantly. 

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