High Performance Polymers

Functional bismaleimides containing γ-lactone, carboxyl, aldehyde, hydroxyl, azomethine or cinnamoyl groups were synthesized from maleimido benzoic acid via its acid chloride with phenolphtaleine, 5,5′-methylene-bissalicylic acid, 5,5′-methylene-bissalicylaldehyde, glycerol, tartaric acid and 3,4-bis(hydroxyethan-2-tioether)-p-maleimidobenzoic acid, by simple condensation or polymer analogous reactions on some of these reactive bisimides.

The monomers were characterized by IR, ¹H-NMR and elemental analysis. The DSC curves of all the samples showed an exotherm in the temperature range of 134–310 °C, which is attributable to curing reactions. Thermogravimetric analysis of the uncured resins indicated good thermal stability and a char yield of bismaleimide resins in accordance with the calculated C/H ratio. Their relative thermoxidative stability was evaluated by isothermal gravimetric analysis.

A series of fluorinated poly(imide-ether-amide)s has been synthesized by solution polycondensation of aromatic diamines containing ether bridges between phenylene rings with a diacid chloride incorporating imide, hexafluoroisopropylidene and methylene groups. The polymers were readily soluble in organic solvents like N, N-dimethylformamide (DMF), N-methylpyrrolidinone (NMP), and even in less polar solvents like pyridine or tetrahydrofuran and gave flexible films by casting of such solutions. These polymers exhibited high thermal stability, with the decomposition temperature being above 360 °C and the glass transition temperature in the range 221–246 °C. The polymer films displayed a low dielectric constant, in the range 3.52–3.81, and tough mechanical properties.

New aromatic polyazomethines have been synthesized by polycondensation of terephthalic dialdehyde with aromatic diamines containing preformed phenylquinoxaline rings. These polymers are easily soluble in polar aprotic solvents such as N-methylpyrrolidinone and dimethylacetamide, and even in less polar liquids like tetrahydrofurane and can be cast into thin flexible films or coatings from such solutions. They show high thermal stability with the initial decomposition temperature being above 500 °C and glass transition temperatures in the range 240–292 °C. The very thin polymer coatings deposited by a spin-coating technique onto silicon wafers show a very smooth, pinhole-free surface in atomic force microscopy investigations. The free-standing films of 20–30 μm thickness show a low dielectric constant, which is in the range 3.25–3.56, which is promising for a future application as high-performance dielectrics.

A series of new wholly aromatic and aromatic-aliphatic poly(amide-imide-hydrazide)s were prepared by the direct polycondensation from p-aminobenzhydrazide with various imide ring-containing dicarboxylic acids by means of diphenyl phosphite and pyridine. These polymers had inherent viscosities between 0.60 and 1.17 dl g⁻¹. Most of the poly(amide-imide-hydrazide)s were readily soluble in polar aprotic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) and could be solution cast into light yellow, transparent, flexible, and tough films. These poly(amide-imide-hydrazide)s had T _g in the range 122–211 °C and could be thermally cyclodehydrated in the solid state to the corresponding poly(amide-imide-1,3,4-oxadiazole)s approximately in the range 250–400 °C, as evidenced by the differential scanning calorimetry thermograms. The thermally converted oxadiazole copolymers exhibited T _g in the range 120–271 °C and did not show significant weight loss before 380 °C in air or nitrogen. Effects of structural changes such as polymethylene length and the nature of the diacid monomers on the properties of polymers were studied.

Polymers have been prepared by the Diels–Alder reaction between novel bis(isobenzofuran)s and bis(phenylacetylene)s containing preformed phthalimide rings. The initial polymer undergoes a thermal rearrangement without volatile evolution that effectively prevents a retro Diels–Alder reaction from occurring. The polymers were soluble in common organic solvents such as chloroform, N-methyl-2-pyrrolidinone, N, N-dimethylacetamide and chlorinated aromatic solvents. The polymers exhibited glass transitions ranging from 251 to 359 °C and a 10%weightloss ranging from 451 to 486 °C in air and 482 to520 °C in helium as determined by thermogravimetric analysis. Thissynthetic approach offers advantages over other Diels–Alder polymerizations since no volatile by-products are generated and a thermal rearrangement eliminates a retro Diels–Alder reaction.

A series of new oligomeric disperse dyes were prepared by coupling various diazonium salts of aryl ether to a 2-naphthol-formaldehyde oligomer. They were characterized in terms of their softening points, colour, solubility and infrared and UV–visible spectral studies. The structural property relationships were discussed. The dyeing on polyester and nylon resulted in yellow, orange and pink-to-redcolouration having good to excellent light-fastness and washing-fastness properties.

PETI-5 (5000 g mol −1) is a relatively new adhesive and composite matrix that exhibits good processability and excellent properties. However in the fabrication of complex composite parts (i.e. skin stringer and support frames), better processability would offer distinct advantages. In an effort to improve the processability of PETI-5, a novel reactive additive was prepared and used to formulate blends. The reactive additive is a mixture of relatively simple phenylethynyl containing imides. As such, it exhibited solubility in a variety of solvents such as N-methyl-2-pyrrolidinone, a relatively low softening temperature ∼185°C) and a low melt viscosity (∼0.1–0.3 Pa s at 250°C). Neat resin blends prepared by physically mixing imide powders of the reactive additive and PETI-5 were thermally and rheologically characterized. Blends were also prepared by mixing NMP solutions of PETI-5 amide acid and the reactive additive (imide form). These solutions were subsequently used to prepare adhesive film and unidirectional carbon fibre tape using unsized IM7 fibre. The reactive additive/PETI-5 blends were used to fabricate titanium adhesive panels and composites under 0.54 MPa or less for 1 h at 350–371°C. The effect of reactive additive content on the physical, rheological, adhesive and carbon fibre laminate properties was determined. One formulation exhibited a decrease in melt viscosity (i.e. improved processability) without effecting open hole compression, compression properties after impact or microcrack behaviour. The neat resin, adhesive and composite properties of these reactive additive/PETI-5 blends and their cured polymers will be discussed.

Novel monomeric dyes have been prepared by diazotization of 2,6-dibromo-4-nitroaniline and coupled with various N-arylmaleimides. The polymeric dyes were prepared by free radical polymerization of monomeric dyes. The resultant dyes were characterized by IR spectral studies, intrinsic viscosity, thermogravimetry analysis, elemental analysis and molecular weight was characterized by VPO. The monomeric dyes were also characterized by elemental analysis and IR spectra. The purity of all the dyes were checked by thin layer chromatography and they have also been applied on nylon and polyester fibres as a disperse dye. These dyes have been found to give various colour shades with good to very good depth and levelness on each fibre. The percentage dye bath exhaustion on different fibres have been found to be good to very good. The light, washing, rubbing, perspiration and sublimation fastness properties of the dyed fibres has been found to be very good to excellent.

Two methylnadimide end-capped polyimides have been prepared by a new water synthesis procedure and their properties compared to similar polyimides synthesized in the conventional solvents, cresol and NMP. The water method has been shown to be a practical alternative for the synthesis of a wide range of polyimides with no evidence of contaminating polyamic acids. The present results showed that with appropriate adjustment of the synthesis conditions very useful methylnadimide end-capped polyimides could be obtained. It was found that the amount of methylnadimide end-cap was reduced under 180°C synthesis conditions, and even at lower temperatures with prolonged heating, and that the water reaction is best carried out at 165°C for these polyimides. One of the uncured resins, Polyimide 1 was quite soluble in common solvents allowing complete characterization. It was found that the amount of endcap introduced by either conventional or water synthesis procedures was less than the theoretical maximum. Examination of the cured neat resin from polyimide 1 showed it to consist of a portion of insoluble, possibly cross-linked, material and a considerable amount of soluble polymer of wide molecular weight distribution. The potential usefulness of these polymers as high-temperature composite matrices was indicated by the excellent tensile properties of polyimide 2B, which on curing produced a tough voidless polymer with a tensile strength of 120 MPa, a modulus of 3.9 GPa and a strain at break of 9.7%.