Imide, acetylene-terminated

Landis, A. L. Chemistry of Procesible Acetylene-Terminated Imides, Pinal Report, AFWAL/ML Contract F33615-82-C-5016, August 1983. 

About 1970, research was initiated under Air Force funding on acetylene-terminated imide oligomers (ATI) which could be thermally chain extended through the acetylenic end-groups (33, 34). This effort resulted in the development of HR-600 (Eq. 9) and subsequent commercialization by Gulf Oil Chemicals Company in the form of Ther-mid -600. Neat resin properties of HR-600 are presented in Table IV while preliminary composite properties are given in Table V. 

Table IV. Cured Acetylene-Terminated Imide (HR-600) Properties1 2...

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. 

Of all the thermosetting imide oligomers discussed in this article, the totally aromatic acetylene terminated imides are the most promising because their... 

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]. 

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. 

Around 1970, the US Air Force funded a program on acetylene terminated imide oligomers and the first patent was filed by Hughes Aircraft [67] and has been described in the literature [68]. Benzophenone tetracarboxylic anhydride was condensed with an aromatic diamine and 3-ethynylaniline to give either an amide acid soluble in acetone, or a fully imidized structure, soluble in NMP. 

The ethynyl terminated imide oligomer work was initially reported in 1974. Neat resin and composite " properties for cured acetylene terminated imide oligomers have been reported. These materials were initially designated HR-600 and later Thermid -600 (60). The ethynyl terminated imide oligomer in structure 8 is representative of this class... 

St. Clair et used the concept of sequential semi-IPNs to produce two unique IPNs which are based on acetylene-terminated imide oligomers and thermoplastic polyimides, particularly a material designated LARC-TPI. Pater and others used the concept of simultaneous semi-IPNs to make semi-IPNs which are based on PMR-15 mixed with such materials as LARC-TPI, NR150B2 and Thermid 600 polyimides. Other examples of semi-IPNs which fit into the category of high temperature materials include thermoplastic modified bismaleimides (BMI). As one example, BMI has been mixed with condensation polyimides such as PI20280 or with terminated poly (arylene ether ketone) oligomers. The observed miscibility in semi-IPNs which are based on thermoplastic BMIs was found to be further improved when a BMI and thermoplastic both prepared from aromatic diamines were blended. ... 

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. 

The Michael addition reaction of dimercaptodiphenylether with N-(3-ethynyl phenyl) maleimide allowed the synthesis of ethynyl-terminated imido-thioether as shown in Fig. 50 (139). This acetylene terminated imidothioether was blended with acetylene terminated polyarylene ether oligomers of different molecular weights and tested as composite resins (140). Blends of functionalized thermoplastics such as the acetylene terminated polyarylene ethers with brittle high-Tg imide resins are finding increased attention for tough high-Tg composites. 

Rezac, M. E., and Schoberl, B. (1999). Transport and thermal properties of poly (ether imide)/acetylene-terminated monomer blends, J. Membrane Sci. 156, 211. 

Murphy et al. [73] studied the cure and degradation of an acetylene-terminated N-labelled poly(imide) using N CPMAS NMR. Initially, the conversion of the amic acid to the imide precursor was followed. Four resolved peaks are observed due to amide and imide either attached to a phenyl ring or at the terminal position. Measurements of the rate of crosspolarization, and the dipolar dephasing experiment, assisted in the assignment to the spectra. Very different rates of cross-polarization (1/Tnh), and values of Ti, were measured for the various structures. Imidization was incomplete after heating to 670 K for 1 h, a result at variance with the results of... 

In a later study. Swanson and coworkers [81] studied the cure of acetylene-terminated poly(imide)s selectively labelled at various positions with nuclei. Curing of the sample, labelled at the imide carbonyl group, confirmed the completion of the imidization reaction on heating. The product of addition onto the carboxyl group was not observed. Four new peaks were identified in the spectrum of the cured sample labelled at the Ci-acetylene group, while a similar result was obtained for the sample labelled at the C2-acetylene position. Analysis of these results rules out the participation of coupling reactions and the biradical mechanism, which would produce triple-bond structures, but confirms the presence of the product of cyclotrimerization and Friedel-Crafts reactions. The latter mechanism is confirmed from the presence of small peaks due to aliphatic carbons in the spectra of the materials labelled at the acetylene groups. 

NMR spectroscopy and in particular solid-state NMR spectroscopy proved to be a powerful method for studying the mechanism and extent of reaction in complex poly(imide) materials. In particular, during the cure of BMI resins, careful use of C CPMAS NMR indicated that measurements of the extent of cure by DSC were significantly overestimated [86, 87]. This article demonstrates that NMR spectroscopy has been able to characterize the structure of condensation poly(imide)s and, more successfully, the cure of BMI, PMR and acetylene-terminated resins. 

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). 

Addition-type polyimides, which are thermosetting resins, were developed to improve the processability of polyimides, but their thermal stability is severely degraded by the presence of aliphatic bonds in place of the aromatic nuclei. However, the adhesive strength has been evaluated for the bismaleimide- (Section 4.3.4.1), bisnadimide- (Section 4.3.4.2) and acetylene-terminated (Section 4.3.4.3) imide oligomers. 

By thermally induced isomerization of an isoimide to an imide, a series of molecular composites with polyarylsulfone, polysulfone and an acetylene terminated isoimide thermosetting resin were obtained [37]. After two flexible polymeric compounds were blended in solution, films were cast and the isomerization process was carried out. The thermally treated films were insoluble and showed no sign of phase separation. 

Acetylene-terminated oligoimides provide excellent thermal resistance, high service temperature, low moisture absorption and high strength, that is, the best performance of the end-capped imides. However, the main difficulty for the commercial use of these systems is the difficulty in their preparation [340,341],... 

In fact all these properties were unavailable in conventional materials but may be covered by aromatic and heterocyclic Unear and thermosetting resins such as acetylene terminated resins, bismaleimides, polyetherimides, polyamide-imides, polybenzimidazoles, pol3dmides, polyetherketones, pol3qjhenylquinoxalines, polyphenylensulfides, polysulfones derivatives, polyst5nylp3nidines, fluoropol3mers, silicones, etc. 

A more developed acetylene terminated heterocyclic system is the aromatic imide system, consisting of two oligo-... 

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

A marginal production is based on the acetylene-terminated oUgoimides, and a proprietary composition has been used at National Semiconductors. In this latter example, the die attach material is prepared from a PMDA—ODA polyamic acid solution in NMP (DuPont PI 2561) mixed with y-amino-propyltriethoxysilane and loaded with silver flakes. The adhesive composition is used to bond semiconductor dice in ceramic packages with a first eure at 125 and 180°C for 2 h each with a final imidization occurring under vacuum when the ceramic lid is sealed with a glass frit at 400—450 °C. 

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