Acetylenic end-groups

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. 

Thermid MC-600, a low melting oligoimide with acetylene end groups was first developed at the Hughes Aircraft Co. [54, 55] and is now produced by the National Starch and Chemical Corp. The structure is based on all meta linked diamine 1,3-bis(3-aminophenoxy)benzene for better processability. 

Siloxane containing oligoimides with acetylene end groups were reported to exhibit good processability and good adhesive properties [64]. 

In CF3COOH the allenic end group of neoxanthin (38) is converted to the acetylenic end group [80] and with concentrated HC1, a chloride is added to the allene [10]. The blue oxonium ion 40 is converted to a yellow, cyclic hemiketal 41 by treatment with KOH. The hemiketal 41 is... 

A second type of polyimide resin is based on a prepolymer that is completely imidized, but has acetylenic end-groups (triple bonds) which can then cure by addition polymerization (Fig. 3.11). These resins do notrequire high curing temperatures and do not evolve water during cure as do the polyamic acid prepolymers. The bismaleimides are yet another variation... 

Oligophenylenes with acetylene end groups also form branched polymers. These compounds can be cross-linked, presumably by cyclotrimerization of the acetylene groups, with catalysts such as titanium (IV) chloride/diethyl aluminum chloride. The prepolymers are soluble and can be moulded with simultaneous hardening. They are suitable for corrosion-resistant coatings. 

Prepolymeric imides with norbornene end groups, I, cross-link during normal polymerization, and those with acetylene end groups, II, presumably cross-link by trimerization to benzene rings ... 

Polyphenylquinoxalines were cross-linked by acetylenic end-groups (Fig. 3.52), giving Tg = 321°C and good resistance to hot humid aging, but the addition of aliphatic hydrocarbon structure apparently sacrificed heat-aging resistance. Propargyl ether of bisphenol A (Fig. 3.53) was cured to a thermoset plastic with = 360°C. 

In principle the conversion of carotenoids with an allenic end group of the type present in neoxanthin (1) acetate to carotenoids with acetylenic end groups by HCI/CHCI3 or by POCI3 in pyridine (41, 105) or to products with chlorinated P-type end groups by HCI/CHCI3 (41, 105) could be useful for stereochemical considerations. 

For modular synthesis of ABC-type triblock copolymer, two successive CuAAC reactions have to be performed on the central polymer chain (B block). To accomplish this, the B block polymer having both azide and acetylene end groups (heterotelechelic B) has to be used and, moreover, one of the termini has to be protected in order to prevent linear chain extension (cf Scheme P12.2.1) or formation of cyclic products (Scheme P12.4.1). In a straightforward methodology, the terminal acetylene moiety on B is protected and the azide terminus is used to carry out the rst coupling reaction to join the preformed A or C block. Next, the acetylene moiety is to be deprotected to make it available for the second coupling reaction to join the remaining C or A block. 

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