Cyclic polyimide

A new class of cyclic polyimides, (VI), was prepared by Ding [6] and used in electronic applications. 

The conversion of polyamic acids into polyimides - imidization or dehydrocyclization - consists of the intramolecular formation of water from the polyamic acid to form a cyclic polyimide. It can be carried out in two ways, thermally and chemically. 

Polyimides are polymers incorporating the imide group in their repeating unit, either as an open chain or as closed rings. However, only cyclic imides are actually of interest concerning polymer chemistry. Thus, under the generic name polyimides, we will exclusively refer to cyclic polyimides in this chapter. 

Although polyimides can have an open-chain structure, cyclic polyimides have found more use because they are more thermally stable than open-chain polyimides. The polyether-imide prepared from pyromellitic dianhydride and 4,4 -diaminodiphenyl ether has found use in high temperature coatings, adhesives, and structural plastics. The reaction involves rapid formation of the polyamide, called polyamic acid, followed by a high-temperature ring closure step. 

The preparation of imides from reaction of isocyanates with anhydrides dates back to the early days of organic chemistry [96]. With the advent of polyimide chemistry in the early 1960s, this chemistry was soon explored for the synthesis of polyimides. However, in contrast to the preparation of polyimides via thejr poly(amic acid) intermediate, the reaction of aromatic dianhydrides with aromatic diisocyanates is much less understood. The reaction of aromatic dianhydrides with aliphatic or aromatic diisocyanates is believed to form a cyclic seven-membered intermediate which then splits out C02 to form the polyimide [97], see Scheme 27. The addition of water, which has been reported to accelerate the anydride/isocyanate reaction, can result in several transformations of either the anhydride or the isocyanate reagent, see Scheme 28... 

Other Polymers. Besides polycarbonates, poly(methyl methacrylate)s, cyclic polyolefins, and uv-curable cross-linked polymers, a host of other polymers have been examined for their suitability as substrate materials for optical data storage, preferably compact disks, in the last years. These polymers have not gained commercial importance polystyrene (PS), poly(vinyl chloride) (PVC), cellulose acetobutyrate (CAB), bis(diallylpolycarbonate) (BDPC), polyethylene terephthalate) (PEL), styrene—acrylonitrile copolymers (SAN), poly(vinyl acetate) (PVAC), and for substrates with high resistance to heat softening, polysulfones (PSU) and polyimides (PI). 

Although rigid-rod poly(p-phenyleneterephthalamide) analogues having alkyl side chains did not contain cyclic polymers, the polycondensation of silylated m-phenylenediamine and aliphatic dicarboxyhc acid chloride afforded cyclic polyamides predominantly (Scheme 49) [187]. Furthermore, cyclic polymers were also produced in polycondensations for polyesters, poly(ether ketone)s, polyimides, and polyurethanes [183]. These examples are the products in polycondensation of AB monomers or in A2 + B2 polycondensations, but cyclization of oligomer and polymer was also confirmed in polycondensation of AB2 monomers [ 188-195] and in A2 + B3 [ 196-202] and A2 + B4 polycondensations [203-206], which afford hyperbranched polymers. 

Aluminum atom reactions are relevant to interfacial chemistry associated with aluminum-polyimide junctions. Al deposited under ultra high vacuum will reduce surface carbonyl functional groups (22). MVS co-condensation experiments show that besides ketones, aldehydes and epoxides, atomic aluminum will deoxygenate ethers. Chapter 7 of the monograph by Klabunde (12) includes tables of deoxygenation products of a variety of cyclic and acyclic ketones and ethers. 

This paper describes a process for activating polyimide surfaces for electroless metal plating. A thin surface region of a polyimide film can be electro-chemically reduced when contacted with certain reducing agent solutions. The electroactivity of polyimides is used to mediate electron transfer for depositing catalytic metal (e.g., Pd, Pt, Ni, Cu) seeds onto the polymer surface. The proposed metal deposition mechanism presented is based on results obtained from cyclic voltammetric, UV-visible, and Rutherford backscattering analysis of reduced and metallized polyimide films. This process allows blanket and full-additive metallization of polymeric materials for electronic device fabrication. 

A list of redox potentials for the first ( E°), second (2E°), and third (3E°) electron reduction couples for different polyimide films is provided in Table I. The potentials were measured by cyclic voltammetry of polyimide films on an electrode surface and represent the average of the cathodic and anodic peak potential for the respective redox couple. 

Cyclic voltammetry of these compounds shows that the first electron reduction (redox couple) is reversible in aprotic electrolyte solutions. A one-electron reduction of these compounds (except TKDE) results in the corresponding radical-anion form (14). Under aprotic and 02-free conditions the anion forms are sufficiently stable for use as reducing agents for the reduction of polyimide films. Reducing agents also can be generated chemically, as for example, reacting benzoin and potassium l-butoxide under alkaline conditions leads to the benzil radical-anion. 

Redox-Mediated Metal Deposition. A reduced polyimide surface can function as a reducing substrate for subsequent deposition of metal ions from solution. For metal reduction to occur at a polymer surface, the electron transfer reaction must be kinetically uninhibited and thermodynamically favored, i.e., the reduction potential of the dissolved metal complex must be more positive than the oxidation potential of the reduced film. Redox-mediated metal deposition results in oxidation of the polymer film back to the original neutral state. The reduction and oxidation peak potential values for different metal complexes and metal deposits in nonaqueous solvents as measured by cyclic voltammetry are listed in Table III. 

The thermal and oxidative stability of polyimides is thonght to be related to the combination of both the five-membered cyclic imide ring and the natnre of the aromatic ring directly connected to the nitrogen (Figure 6). 

Suspension polycondensation of pyromellitic dianhydride and 3,5-diamino-1,2,4-triazole yielded triazole-containing polyimide beads that were used as a support for Mo02(acac)2 [60]. The resulting catalyst showed high activity and selectivity in the epoxidation of cyclohexene and cycloctene as well as in the epoxidation of noncyclic alkenes such as styrene, 1-octene, and 1-decene with TBHP. The catalyst could be recycled 10 times and activity decreased significantly in the case of 1-octene epoxidation whereas activity remained high in the epoxidation of cyclic alkenes. 

The graphite fiber reinforced triaryl-s-triazine ring (TSTR) cross-linked polyimides with ring-chain structures have good mechanical properties at elevated temperatures. On pyrolysis, the TSTR cross-linked polyimides were converted to refractory type materials which are believed to be graphitic type ladder polymers containing some nitrogen in their cyclic structures. 

The most common conformal coatings are derived from polyurethanes, acrylics, and epoxies the more special formulations for high-temperature performance are based on silicones, diallyl-phthalate esters, and polyimides. An example of a vapor deposited conformal coating is Parylene. It is obtained by vapor deposition of p-xylylene, which is formed as a transient by dehydrogenation of p-xylene at high temperature, and polymerization on the surface of the object to be coated. Because p-xylylene monomer is not stable, it is advantageous to work with the cyclic dimer, di-p-xylylene (paracyclophane), which, upon heating under reduced pressure, will produce the transient monomer which converts to the polymer at low temperatures. 

As shown in Figure 20.11, the microstructures are transferred from the master to the polymer by stamping the master into the polymer, which is previously softened by heating above its glass transition temperature. This method is limited to thermoplastic polymers, and the technique has been used successfully on a variety of polymers, including polycarbonate,i polyimide, cyclic olefin copolymer, and PMMA. The main parameters to control are the surface quality, temperature uniformity, and chemical compatibility of the master. 

To clarify the mechanisms of plastic flow of linear-chain polymers we also consider polyimides (PIMs), which make up a large family of stiff and thermally stable polymers of outstanding performance (Bessonov et al. 1987). Polyimides contain cyclic imide groups as shown in Fig. 2.4 in the main chain. From this very... 

Charge transport in an organic material is believed to be governed by a hopping process that involve a redox reaction of the charge transport molecules. Cyclic voltammetry (CV) is a preliminary characterization method to determine the redox properties of polymeric materials. One pair of redox waves was observed in these polymers. As shown in Fig. 2.11, polyimide DADT/DSDA... 

The cyclic main chain is more definite in polyimides synthesized from trimellitic anhydride and aromatic diamines ... 

All commercially used polyimides contain cyclically bound imide groups. In these cases, the imide group here may have been present in the initial monomer or it may be first formed during the polyreaction. In addition, cross-linked or un-cross-linked products may be produced by either of these synthetic types. 

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