Amide acid prepolymers

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. 

Schucker R. C (1992), Multiblock polymer comprising a first amide acid prepolymer, chain extended with a compatible second prepolymer, the membrane made thereof and its use for the separations,... 

Polymerization of the dianhydride and diamine proceeds through an intermediate poly(amide acid) stage before ring closure converts the adjacent acid and amide groups to the polyetherimide (94). The polymerization can be carried directiy to the polyetherimide as a single-step process, or first to an ainide—acid-containing prepolymer, which can be isolated, and then to the polyetherimide. 

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. 

In order to control the pore texture in carbon materials, blending of two kinds of carbon precursors, the one giving a relatively high carbonization yield and the other having a very low yield, was proposed and called polymer blend method [112], This idea gave certain success to prepare macroporous carbons from poly(urethane-imide) films prepared by blending poly(amide acid) and phenol-terminated polyurethane prepolymers [113]. By coupling this polymer blend method with... 

Through the synthesis of poly(urethane-imide) films and their carbonization, carbon films were obtained whose macropore structure could be controlled by changing the molecular structure of polyurethane prepolymer [164-166]. Poly(urethane-imide) films were prepared by blending poly(amide acid), which was synthesized from pyromellitic dianhydride (PMDA) and 4,4 -oxydianiline (ODA), and phenol-terminated polyurethane pjrejwlymers, which were synthesized through the reaction of polyester polyol with either hexamethylene diisocyanate (HDI), tolylene-2,4-diisocyanate (TDI) or 4,4 -diphenyknethane-diisocyanate (MDI). The reaction schemes of two components, poly(imide) (PI) and poly(urethane) (PU), are shown in Fig. 46a). 

The synthetic route for preparing the addition polyimide adhesive LARC-13 is displayed in Fig. 1. Appropriate quantities of 3,3 -methylenedianiline (m,m -MDA)f nadic anhydride (NA), and 3,3, 4,4 -benzophenone-tetracarboxylic acid dianhydr ide (BTDA) are combined in an amide solvent at a concentration of 50% solids by weight to form a 1300 molecular weight amic acid. This amic acid prepolymer is used as the adhesive resin and is later cured to the cross-linked polyimide by the removal of solvent,... 

The segmented polyamide elastomers are synthesized from MDI (4,4 -diisocyanato-diphenylmethane) and dicarboxylic acids and a carboxylic acid terminated aliphatic polyester, polycarbonate or polyether prepolymer with an average molecular weight of M = 500-5000. The dicarboxylic acids used as hard segment extenders are adipic and azelaic acid. Also, poly(ester amide) alloys are obtained using nylon-6,6 or polyesters (PEA/PBT). 

The prepolymer approach which worked well for piperazineamide interfacial membranes was not useful in the case of FT-30 and its analogs. Poor solubility of aromatic amide precursors in aqueous media was the main obstacle. A patent application has appeared on the use of prepolymer formed from 1,3-benzenediamine and trimellitic anhydride acid chloride.66 This prepolymer contains a free carboxylate group and is soluble in water as the sodium salt. A membrane is obtained by reaction of this intermediate with trimesoyl chloride, followed by a curing step at 110° to 130°C. Salt rejections of 98.5 to 99.1% on 2,000 ppm sodium chloride solution at 200 psi were obtained fluxes were 4 to 11 gfd. 

Foams are prepared similar to PI resins by heating a prepolymer of poly(amide amic acid). The water during the reaction will cause foaming. In detail, the process consists of ... 

Pulverizing the poly(amide amic acid) resin prepolymer, into the... 

In practice, therefore, diamines alone are converted with urea in the melt or in phenol. The reaction possibly proceeds via the intermediate formation of isocyanic acid. The prepolymer obtained by heating to 140-160° C is then condensed out under vacuum at about 250° C. Labile end groups, considered to be urea or isocyanate groups, are stabilized by addition of monobasic acids, amines, or amides, etc. The polyurea formation reaction is an equilibrium reaction transureidation is thus possible ... 

Forming an optimal molding may require the addition of an external or internal lubricant to the formulation. Lubricants arc added in only small amounts, up to 1 wt %. External lubricants are insoluble in the phenohe matrix resin and are often non- polar materials such as parafiins and waxes. External lubricants act as mold release agents. In contrast, internal lubricants improve melt homogeneity, lower viscosity, and lower injection pressure. Therefore, internal lubricants such as fatty alcohols, fatty acid salts, acid esters, and acid amides must be fully soluble in the phenohe prepolymer [1]. 

One of the developments that has been widely publicized is the development of polyester amides by Monsanto. According to U.S. Patent 3,650,999, these copolymers, trade named Montac, are made by reacting an aromatic polyester, such as PET or PBT, with dimer acid to form an acid-terminated prepolymer which is then reacted with a diamine to produce blocked polyester-amides with melt points, flexibility, and unique adhesive characteristics suitable for structural adhesives. These block copolymers have a crystalline block derived from the polyester and an amorphous block derived from the polyamide. Typical properties of copolymers mentioned in the patents are shown in Table 17. 

---