Acetylene Terminated Polyimides

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. 

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. 

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

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.

Figure 3.11 Acetylene-terminated polyimide resin structure.

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. 

TABLE 3.52 Acetylene-Terminated Polyimide Cured Properties... 

FIGURE 3.47 Cross-linking acetylene-terminated polyimides. 

THERMID 600 National Starch Acetylene-terminated polyimide solution. 

Figure 19 Acetylene-terminated polyimide precursors synthesised by reacting BTDA 18 with less than the stoichiometric balance of 3,3 -(l,3-phenylenedioxy) bisbenzeneamine 44 and the complement to stoichiometry of 3-ethynylbenzeneamine 45 as end-capping agent. Low molecular weight polyamic acid 46 is then chanically cyclised to poly(isoimide) 47 or thermally cyclodehydrated to give polyimide 48.

Titanium alloy (Ti6Al4V) test samples were bonded with acetylene-terminated polyimide oligomers 51, with degree of polycondensation n = 1, 2 and 3, under... 

Several papers have appeared describing water permeation, electrical conductivity, cross-linking efficiency of curing polymers, and the kinetics of sulphur dioxide sorption in polyimides. Carbon-13 n.m.r., has been used to examine acetylene-terminated polyimides. ... 

Mathews DA (1963) Review of the lithium chloride radiosonde hygrometer. In Proceedings of the conference on humidity and moisture, vol VI, Washington, DC, pp 219-227 Matsuguchi M, Sadaoka Y, Sakai Y, Kuroiwa T, Ito A (1991) A capacitive-type humidity sensor using cross-linked poly(methylmethacrylate) thin films. J Electrochem Soc 138 1862-1865 Matsuguchi M, Sadaoka Y, Nosaka K, Ishibashi M, Sakai Y, Kuroiwa T, Ito A (1993) Effect of sorbed water on the dielectric properties of acetylene-terminated polyimide resins and their application to a humidity sensor. J Electrochem Soc 140 825-829... 

Because of the importance of epoxy resins, it is not surprising that they received early attention from researchers using the soUd-state NMR techitique [43,44]. A number of other crosslinked systems have been investigated, including acetylene-terminated polyimide resins [45,46], poly(p-phenylene) [47], 2-propenenitrile polymer with 1,3-butadiene and ethenylbenzene (ABS) resins [48], furfuryl alcohol resins [49], phenolic resins [50], acrylic resins [51,52], melamine-formaldehyde resins [53], polynuclear hydroxymethyl phenol (resol)-formaldehyde resins [54], and plasma-polymerized materials [55]. 

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