High Performance Polymers

The development of physical aging in four amorphous poly(aryl ether ketone)s at temperatures below the glass transition temperature, T_g , was studied using differential scanning calorimetry (DSC). The change in enthalpy lost on aging, determined by scanning through T_g , was used to determine the kinetics of the aging process through fitting to the Cowie–Ferguson model. The kinetics of aging were found to depend on the ketone–ether ratio as well as the substitution pattern of the polymers. The maximum enthalpy lost at equilibrium, ΔH∞, was found to be a linear function of the change in heat capacity at T _g, ΔC _p(T_g), and the degree of supercooling, ΔT. A composite curve incorporating T _g values from physical aging and dynamic mechanical studies, covering 15 decades, could be fitted to the Volger–Fulcher equation and demonstrated that physical aging is an extension of the glass forming process.

Adhesion properties of various thermoplastic polyimides and copolyimides were studied in order to develop suitable heat resistant adhesive film with excellent hot-melt processability under moderate conditions and to discover the effect of polysiloxane units introduced as soft segments on the bond strength. The single-lap shear strength of the steel joints adhered with the polyimides and copolyimides was found to depend on the structure of the aromatic components: linear aromatic polyimides with multi-phenylene linkages and meta linkages, particularly those prepared from 3, 3′ 4, 4′-diphenylethertetracarboxylic dianhydride and 3, 3′ 4, 4′-benzophenonetetracarboxylic dianhydride, showed an increased lap shear strength. The introduction of polysiloxane segments into the polymide backbone increased not only the processability of adhesion, but also the lap shear strength, significantly. However, the shear strength was lowered at high temperature because the cohesive force of the polymer decreased with decreasing glass transition temperature. The adhesion strength was also influenced by such bonding conditions as pressure and temperature.

An amino-terminated oligoimide was prepared by Michael addition reaction of N, N′-1, 4-phenylene bismaleimide (PBM) and 4, 4′-diamino-diphenyl methane (DDM) at a PBM–DDM ratio of 1:2. The poly(amido-imide)s (PAIs) were prepared by condensation of this PBM–DDM oligoimide with various aliphatic bisesters. The resultant PAIs were characterized by elemental analysis, IR spectral studies, number-average molecular weight (M _n), estimated by nonaqueous conductometric titration, and thermogravimetry. The curing reaction of the epoxy resin–, namely diglycidyl ether of bisphenol-A (DGEBA)–, PAI system was monitored by differential scanning calorimetry (DSC). Based on cure temperature, the glass- and carbon-fibrereinforced composites (i.e. laminates) of the PAI–epoxy resin system have also been prepared and characterized.

The UV stabilizers 2-OH-4-allyloxybenzophenone and its oxime were prepared. They were copolymerized with styrene to give copolymers containing 2–8% UV stabilizers. The films were exposed to UV light and tested for any change in the carbonyl index, hydroxyl index, tensile strength, elongation at break and evaporation loss. The stabilization efficiency was evaluated by comparing with similar testing on pure polystyrene.

Molecular properties of the TGM-3 photopolymer have been investigated using a HYPERCHEM 4.0 computer package. The geometry of this photopolymer was successfully optimized and the TGM-3 structure obtained shows a very complicated non-linear shape. The total charge density of TGM-3 is strongly nonuniform. C=O double chemical bonds are roughly perpendicular to a bent central chain. We have calculated a value of the HOMO–LUMO energy gap which is not in agreement with our experimental data for the fundamental absorption edge. A possible origin of this difference is suggested. One can expect that the TGM-3 properties have a strong influence on its solid many-component mixtures with other photopolymers.

In addition to the homopolyesters, poly(4-hydroxybenzoate) and poly(4-phenylene terephthalate), two series of copolyesters have been prepared with a systematic variation of the molar ratio. The first series was prepared by polycondensation of 4-acetoxybenzoic acid, terephthalic acid and acetylated hydroquinone in a liquid inert reaction medium at 400 °C. The second series was prepared under the same reaction conditions but from silylated 4-acetoxybenzoic acid and silylated terephthalic acid and showed a considerably higher 4-hydroxybenzoate/terephthalate ratio than expected from the feed ratio. The composition of these copolyesters was checked by 1H NMR spectroscopy after hydrolysis. All copolyesters proved to be highly crystalline regardless of the molar composition. WAXS measurements were conducted with synchrotron radiation up to 450 °C. These WAXS patterns indicate a gradual phase transition between 150 and 300 °C which is not detectable in the DSC curves. For the copolyesters containing > 50 mol% or 4-Hybe (4-hydrobenzoic acid) units one or two reversible first-order phase transitions were found in the DSC traces. Electron microscopy revealed that all these copolyesters are crystal powders consisting of particles of irregular shape. However, copolycondensations of silylated 4-acetoxybenzoic acid with silylated terephthalic acid and acetylated hydroquinone yielded copolyesters with a ‘potato-chip morphology’.