Acetylenes terminal, addition

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. 

A substantial effort in our laboratory has been directed toward the synthesis and characterization of acetylene-terminated (AT) matrix resins. The most significant feature and driving force for the effort is that the thermal induced addition reaction provides a moisture Insensitive cured product. This technology offers a wide variety of thermoset resins for various high temperature applications. Backbone structural design for use temperature capabilities, processing characteristics and mechanical performance has demonstrated the versatility of the AT type systems. 

Acetylene-terminated resins (ATR) bisphenol-based, synthesis, 17-29 thermally curable, 6 Acetylene-terminated sulfone (ATS), thermally curable, 5 Acid values, castor oil prepolymer formation, 241 Addition polymerization... 

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. 

Tandem addition of trimethyltin followed by cyclization in a 1,6-heptadiene system [Eq, (7)] proceeds with surprising efficiency [30]. Oxidative destannylation of the primary product gives a synthetically useful dimethyl acetal. An acetylene-terminated tandem addition is shown in Eq. (8) [31]. 

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

The introduction of acetylene, terminal alkynes or internal alkynes into methylene chloride solutions of iodosylbenzene and triflic acid [1 1, in situ generation of PhI(OH)OTf] results in the production of [j3-(trifluoromethanesulfonyloxy)vinyl]iodonium triflates (equation 172)78,133. Since the -configuration has been determined for selected members of this series (R1, R2 = n-Pr, H n-Bu, H), these reactions appear to proceed via stereoselective anti-additions of PhI(OH)OTf to the alkynes. 

Acetylene terminated (AT) resins are being studied as a new technology to form the matrix of high performance structural composites (1). This class of resin cures by an addition reaction mechanism. Because of the absence of volatile by-product during cure, these resins are easy to process to yield void-free components. These resins also have the advantage over epoxy resins in terms of resistance to deterioration of properties at elevated temperature due to exposure to humid environments (2). 

Dihydrofiirans have seen considerable use as substrates in the Pauson-Khand reaction. The parent compound reacts in excellent yield with acetylene, terminal and internal alkynes. Yields in this system respond very well to the use of catalytic reaction conditions (equation 4). Another unusual experimental modification has also been found by Pauson to be useful in this system addition of tri-n-butylphosphine oxide nearly doubles the product yield in certain cases (equation 37). The role of the added substance is unclear. Addition of phosphine oxide does not always improve reaction efficiency at this time there are no guidelines to indicate when its use might be beneficial. Substituted dihydrofurans give somewhat lower but still acceptable yields the poor regioselectivity in unsymmetrical cases is the more significant difficulty with these substrates (equation 38). 

Vinylidenes have been transferred from a variety of precursors to olefins to produce methylenecyclopropanes . Because of ready intramolecular hydrogen shifts to give terminal acetylenes, the addition of vinylidene to olefins is rather limited to 2,2-disubstituted species. The methodologies so far developed include (1) gem-dibromides, 7, with MeLi, (2) vinyl halides " or vinyl triflates, 8 " with r-BuOK, (3) the fluoride ion promoted decomposition of vinylsilanes, 92 2,243 4 thermolysis of mercuric derivatives, 10, at 250 (5) decomposition of vinylazo compounds, 11, at 25 (6) the alkaline... 

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. 

Besides the condensation PI, there have been two new types of addition Pi s ethynl (acetylenic) and norbornene (nadic) end-capped PI. The acetylene-terminated PI (ATI) was first reported by Bilow and co-workers (52) and the nadic-terminated PI (NTI) (Pig. 8) was derived from the work of Lubowitz (33). An NTI prepared at NASA Langley Center has been designated as LARC-13 (34). When LARC-13 was compared with ATI as the adhesive for titanium, the lap shear... 

Polyphenylquinoxalines (PPQ s) were first prepared in 1967 by Hergenrother (56). In 1975, Koval et al. (57,58) introduced the acetylene-terminated PPQ (ATPQ) (Pig. 10), which is the addition type of PPQ. Resembling ATPI, ATPQ also has shortcomings. The ethynl group hinders the flow of the polymer chain, and the cured ATPQ is less thermal-oxidatively stable than the comparable PPQ. The detailed status of PPQ, as well as other high-temperature adhesives, is discussed by Hergenrother (45). ... 

Addition Cured Acetylene Terminated Polyphenylquin-oxaline Oligomers," Polym. Chem. Preprints, 21,... 

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. 

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. 

Reactions of Hydrocarbons. Several types of reactive hydrocarbon functional groups can be used to polymerize and cross-Unk monomers and ohgomers into thermoset plastics. These include addition polymerization of acetylene-terminated molecules and ring-opening polymerization of strained carbon rings. They also include Friedel-Crafts condensation to form hydrocarbon polymers. 

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. 

A substantial effort in this laboratory has been directed toward the synthesis and characterization of acetylene terminated oligomers for use as addition-curable, moisture-resistant, thermoset systems. Early work on the acetylene-terminated phenylquinoxalines demonstrated the moisture insensitivity of the product generated from the thermal cure. Studies of various difunctional acetylene-terminated monomers has demonstrated that the polymerization is a free radical propogation of the acetylene moiety to a linear conjugated polyene. 

As mentioned in the introduction, the synthesis of telechelics is important to preparative polymer chemistry because of their use as macromonomer precursors (and therefore graft copolymer and network precursors), as precursors to block copolymers, and as the basis of reaction injection molding. Some general reviews on telechelics include those of A they and Heitz. In addition, the synthesis, reactions and properties of acetylene-terminated oligomers were recently reviewed.An extensive discussion of this class of reactive polymers is the subject of a recent book. ... 

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