High Performance Polymers

A new reactive N-substituted maleimide monomer containing an aldehyde function, N-(4-formyl-phenoxy-4′-carbonylphenyl) maleimide (MI-CHO), was synthesized. The radical copolymerization of MI-CHO with styrene was performed at 60 °C in the presence of 2,2′-azoisobutyronitrile as an initiator in dimethylsulfoxide. The copolymerization of MI-CHO with styrene yielded the ‘nearly equimolar’ alternating copolymers for the mole fractions of MI-CHO in the feed ranging from 0.2 to 0.7. The monomer reactivity ratios (r ₁, r ₂) in the polymerization of MI-CHO (M ₁) with styrene (M ₂) and the Alfrey–Price Q ₁ and e ₁ parameters were determined. The thermal properties of the copolymers were investigated by using thermogravimetric analysis and differential scanning calorimetry.

Two series of homopolyimides based on oxydiphthalic anhydride and bisphenol A bisether-4-diphthalic anhydride were synthesized with 12 kinds of aromatic diamines. Several thermo-processable homopolyimides were the focus of further investigation. The structure–property relationships of these homopolyimides were examined as functions of the glass transition temperature (T _g), melting point (T _m), thermal decomposition temperature (T _d), and melt-flowability. The effects of the chemical and higher-order structures on these properties were discussed in this work to obtain an indication for the molecular design of high-performance thermoprocessable polyimides. A series of thermoplastic copolyimides were prepared to achieve higherT _g and T _d without sacrificing thermo-processability. The copolyimides investigated exhibited a comparable or lower melt viscosity, higher T _g and T _d, and higher long-term thermo-oxidative stability than those of ULTEM type polyimides. One of them exhibited a low melt viscosity (4700 poise at 400 °C), a high T _g (224 °C), and excellent thermo-oxidative stability.

The present work was devoted to the investigation of aromaticam in ereactions under the conditions of non-traditional tribochemical synthesis at room temperature in different triboreactors. Experimental data indicate the formation of reactive pre-polymer products of interaction, of low-molecular-weight non-melting and non-soluble pyromellitimide with bismaleimide, running the reaction of migratory copolymerization in the solid phase under the conditions in the vibromixer.

On the example of paraphenylenediamine and terephthalic aldehyde, the principal possibility of Schiff base synthesis has been demonstrated under the conditions in the shear micromixer, and the optimal regime has been determined. The obtained oligomer products contain thermostable fragments and reactive amino and aldehyde end-groups as well as double bonds of the maleimido cycle still remain. This composition allowed us to use them in polyheteroarylene synthesis of different structures in order to modify their properties.

High-temperature polyimide composites with low and stable dielectric properties were produced by thermally curing prepolyimide moulding compounds which were prepared by the wet impregnation of chopped short quartz fibres with a PMR-II polyimide matrix resin solution, followed by the evaporation of the solvent with vigorous stirring. The mechanical properties, thermo-oxidative stability as well as the dielectric and electric properties of the composites were studied. The experimental results showed that the composites exhibit outstanding mechanical properties and excellent thermal and thermo-oxidative stability at temperatures as high as 371 °C. It was revealed that both the dielectric constant (∼3.0) and loss tangent (∼10⁻³) of the composites were not obviously changed with a frequency in the broadband wavelength (1 kHz–20 GHz).

One type of polyetherimide (PEI) modifier was used as modifier of a bismaleimide (BMI) resin. The effects of the modifier content on the thermal properties and morphological structures of the modified BMI resin systems were investigated. As the modifier content increases the miscibility between the two phases increases and the morphological structure of the modified resin changes from a dispersed system to a particle co-continuous structure and to a phase inverted system at 20% PEI content. This increase in the miscibility and the change in the phase structure should result in the improvement of the adhesion properties of the PEI/BMI blend system.

New silicon-containing polyesterimides have been synthesized by a solution polycondensation reaction, in a high-boiling-point solvent, of a silicon-containing diacid chloride (namely bis(p-chlorocarbonyl-phenylene)-diphenylsilane) with certain dihydroxy-compounds having preformed imide rings. All these polymers were soluble in polar amidic solvents, such as N-methylpyrrolidinone and dimethylformamide, and gave thin transparent films on casting their solutions. The polymers exhibited high thermal stability, with the initial decomposition temperature being above 400 °C for fully aromatic structures. Most of these polymers did show a glass transition: those containing only aromatic rings being in the range of 180–236 °C, while those having some ethylene units along with aromatic ones being in the range of 160–178 °C. The dielectric constants of the free-standing polymer films are in the range of 3.04–3.19. Very thin coatings, in the range of tens of nanometres, which were deposited onto silicon wafers, exhibited smooth and pinhole-free surfaces in atomic force microscopy investigations. All these characteristics are discussed and compared with those of related polyester-imides which do not contain silicon.

The melts of aromatic carboxylic acids such as benzoic acid (BA) at 130–160 °C were shown to be excellent media for the one-pot synthesis of high molecular weight, completely cyclicized polyetherimides (PEIs) from the corresponding diamines and tetracarboxylic acid dianhydrides. According to the data on the cyclodehydratation (CD) kinetics of oligomeric amic acid model compounds, the rate of cyclicization of transient polyamic acids in BA at 140 °C is very high, and the polymer chain growth proceeds via the polyaddition of completely cyclicized PEI oligomers with amino and anhydride end groups. Tetracarboxylic acids in BA at 140 °C were shown to react with aromatic diamines to obtain high molecular weight PEIs as well as the corresponding dianhydrides. The effect of the total concentration of comonomers and the presence of an ‘inert’ diluent on the kinetics of the growth of the inherent viscosity in the polycyclocondensation of diamines and dianhydrides is discussed from the point of view of the mechanism of the process. The prospect of a novel synthetic approach in polyimide synthesis is discussed, including obtaining new homopolyimides based on extremely-low-reactivity monomers; new statistical, regular, alternating copolyimides and block copolyimides; two-component blends with one glass transition point, and PEIs based on AB-type heteromonomers.