Polyimides acetylene-termination

Norbomene-terminated imide NR-150B type polyimide Acetylene-terminated phenylquinoxaline Polyphenylquinoxalines with pendent phenylethynyl groups Semi-interpenetrating polyimide networks... 

An interesting approach to thermosetting acetylene-terminated polyimides via the Michael addition reaction has appeared (38). Acetylene-terminated aspartimides are readily prepared ia high yield via two routes, shown ia Figure 7. 

Acetylene terminated polyimide prepolymers have many advantages over conventional polyimides in the areas of processing and solvent resistance. In addition, the presence of the isoimide structure further extends the the utility of these systems by modification of the solubility properties and glass transition temperature. 

Solid state NMR has been used to study polymers of various classes over the past several years. In particular, the technique has been used to study curing reactions in epoxies (12). polyimides (1), and acetylenic terminated sulfones (13). The ability to observe the evolution of the carbons of the reacting species has been clearly shown to provide valuable information which has been difficult or impossible to obtain with other techniques. The use of 13C solid state NMR techniques is essential for the understanding of curing reactions in high temperature polymers in order to be able to correlate the reaction chemistry with the structural and resulting physical properties. 

The idea of synthesizing imide oligomers which carry acetylenic terminations appeared attractive because homopolymerization through acetylenic endgroups occurs without any volatile evolution and provides materials with good properties. Landis et. al (8,9) published the synthesis of such acetylene terminated imide oligomers from benzophenone tetracarboxylic anhydride, aromatic diamine and 3-ethynylaniline via the classical route. As usual, the amide acid is formed as an intermediate which, after chemical cyclodehydration, provides the polymide. Since ethynyl-terminated polyimide is used as a matrix resin for fiber composites, processing is possible via the amide acid, which is soluble in acetone, or via the fully imidized prepolymer, which is soluble in NMP. The chemical structure of the fully imidized ethynyl-terminated polyimide is provided in Fig. 44. 

The key to acetylene terminated polyimides is the availability of the end-capper which carries the acetylene group. Hergenrother (130) published a series of ATI resins based on 4-ethynylphthalic anhydride as endcapping agent. This approach first requires the synthesis of an amine-terminated amide acid prepolymer, by reacting 1 mole of tetracarboxylic dianhydride with 2 moles of diamine, which subsequently is endcapped with 4-ethynylphthalic anhydride. The imide oligomer is finally obtained via chemical cyclodehydration. The properties of the ATI resin prepared via this route are not too different from those prepared from 3-ethynylaniline as an endcapper. When l,3-bis(3-aminophenox)benzene was used as diamine, the prepolymer is completely soluble in DMAc or NMP at room temperature, whereas 4,4 -methylene dianiline and 4,4 -oxydianiline based ATIs were only partially soluble. The chemical structure of ATIs based on 4-ethynylphthalic anhydride endcapper is shown in Fig. 45. 

St. Clair [36] synthesized and evaluated the properties of a semi-2-IPN comprising Thermid 600 (an acetylene terminated imide oligomer from National Starch and Chemical Company) and LaRC-TPI (a thermoplastic polyimide with a Tg of 257 °C). The composition having the ratio of 65 35 of thermosetting Thermid 600 to LaRC-TPI showed the best flexural strength at ambient temperature [36]. 

Maudgal S, STClair TL (1984) Siloxane containing addition polyimides ii acetylene-terminated polyimides SAM PE Quarterly 16 1 6-12... 

Starting materials and solvents were purchased from Aldrich Chemical Co. acetonitrile (ACN), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP) were obtained anhydrous in Sure/Seal bottles and used as received. The polyamic acid of PMDA-ODA (2545 Pyralin) was supplied by DuPont. The soluble polyimide XU-218, derived from 3,3, 4,4 -benzophenone tetracarboxylic dianhydride (BTDA) and diamino-1,1,3-trimethyl-3-phenylindan isomers (DAPI) was purchased from Ciba-Geigy Corp. The acetylene terminated imide oligomer powder (Thermid MC-600) derived from BTDA, aminophenylacetylene, and 1,3-bis (2-aminophenoxy) benzene (APB) was obtained from National Starch and Chemical Company. Kapton Type II (PMDA-ODA) films were obtained from DuPont Co., Apical polyimide films were obtained from Allied Corp., and Upilex Type-S and Type-R polyimide films derived from 3,3, 4,4 -biphenyl tetracarboxylic dianhydride (BPDA) plus p-phenylenediamine (PDA) and ODA, respectively were obtained from ICI Americas Inc. 

The fracture behavior of an acetylene-terminated polyimide has been experimentally investigated. Engineering fracture methods were adapted and applied to small quantities of this material. Miniature compact-tension (CT) specimens were fabricated and subjected to a programmed series of post-cure cycles. Fracture tests were then conducted at room temperature and at several elevated temperatures in a nitrogen purged environment. The fracture toughness was found to vary with temperature and to depend upon post-cure. These Fracture tests clearly discriminate between the specimens resulting from the different cure cycles with only a small investment of material. 

A relatively large quantity (approximately 200 gm) of an aromatic heterocyclic material was available and was used to develop a fracture test method that could be used to characterize materials limited in available quantities. This material is an acetylene-terminated polyimide, known as Thermid 600, which has the molecular structure shown in Figure 1. Although the material is a bit difficult to work with in the 100% solid form, this form was used to fabricate specimens. Cure kinetics and rheological data were measured and used to guide specimen fabrication. 

Figure 3. Data taken at three temperatures measuring the relative displacement between devices in acetylene-terminated polyimides.

The polyimide matrix resin employed in all composites was THERMID 600, a thermosetting resin polymerized from acetylene-terminated oligomers. Its chemical structure is shown below (9). 

Figure 3.11 Acetylene-terminated polyimide resin structure.

Recently, hyperbranched polyimides were obtained by selective orderly reaction only at polymer ends using telechelic polyimides with terminal reactive groups of acetylene, vinyl and acryl [29-33],... 

The gas permeation parameters have also been reported for polymers obtained via ether reaction of epoxy and diamines [57,58], for polymer blends with acetylene-terminated oligomer [73,74] and internal acetylene polyimide [72,75]. The gas permeability of cross-linked internal acetylene-containing polymer, 6FDA-TeMPD/p-intA (4 1) declines from 612 to 186Barrer, while the selectivity, a(C02/CH4) increases from 14 to 25 at 35°C and lOatm [75]. Moreover, this cross-linked 6FDA-TeMPD/p-intA (4 1) membrane is still stable under CO2 pressure of about 47 atm. 

HR-602 - This system represents a different resin chemistry through use of acetylene-terminated polyimide structure. The cure mechanism consists of an addition reaction with no release of volatiles during cure. The intermediate acetylene-terminated polyimide structure is shown below. Reaction to the final cured structure is proposed as a trimerization of the acetylene groups to form an aromatic structure. 

Researchers at IBM Research Center, San Jose, CA, particularly Dr. D. Y. Yoon, have done extensive work with the polyamic acid and polyimide from the reaction of pyromellitic dianhydride and 4,4 -oxydianiline. In private communication. Dr. Yoon reported that the thermally cyclodehydrated polyimide contained 4% isoimide as evidenced by ESCA (Electron Spectroscopy for Chemical Analysis). Dr. Fred Hedberg, AFWAL, Dayton, OH, is using Fourier Transform Infrared Spectroscopy (FTIR) to determine residual isoimide content in the thermally cured product from an acetylene-terminated isoimide oligomer. Dr. Hedberg reported in private communication that the major isoimide band is in the 929-936 cm region. Unfortunately, there are other weak bands in the IR spectra of polyimides which interfere with the isoimide band. The IR spectra of thermally cured polyimides from 3,3, 4,4 -benzophenonetetracarboxylie acid dianhydr ide exhibited... 

For durable bonds, adhesives should be tough. However, many high temperature adhesives (addition-type polyimides, bismaleimides (BMI), and acetylene-terminated resins) are brittle and need to be toughened by elastomers. 

TABLE 3.52 Acetylene-Terminated Polyimide Cured Properties... 

FIGURE 3.47 Cross-linking acetylene-terminated polyimides. 

Polyimides have been cured by synthesizing acetylene-terminated oligomers containing finished imide groups, and these have shown excellent heat resistance, as discussed above (Sec. 3.1.6.3.2). 

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