High Performance Polymers

The application of the dynamic mechanical thermal analysis (DMTA) test method in the study of the effect of storage time on the curing process of sheet moulding compound (SMC) is discussed. Emphasis is placed on following the curing by the study of storage modulus and loss tangent with storage time. Changes in the storage time showed an increase in the storage modulus (log E′) during a room-temperature cure. The loss tangent (tan δ) damping peak occurs as the system is driven into the glassy state by the cross-linking reaction. The SMC displayed a room-temperature log E′ of 8.5 Pa which increased to approximately 9 Pa in the subsequent scan in the DMTA.

The design and operation of a single mode, tunable, cylindrical microwave cavity is described. The cavity has been used to monitor the cure reactions of two epoxy-amine resin systems. The cavity operates at a microwave frequency of 2.45 GHz and a typical power in the range 0–8 W. It is fitted with an adjustable shorting plate which allows six different electromagnetic modes to be tuned. The isothermal cure of the resins MY721/DDS and MY721/DDM was monitored using fibre optics coupled with a Perkin Elmer 1600 FT-IR spectrometer operating in the NIR region. This allowed simultaneous, real time monitoring of the intensities of the primary and secondary amine overtone bands, as well as that of the epoxide groups. The temperature of the resins during cure was monitored by a fibre optic thermometer and was kept constant either by adjustment of the incident microwave power or by on-off switching of the microwave field.

New polyoxaloylesters have been synthesized via interfacial polycondensation of oxaloyl chloride with 2,5-bis(p-hydroxybenzylidene)cyclopentanone I, 2,5-divanillylidenecyclopentanone II, 2,6-bis(p-hydroxybenzylidene)cyclohexanone III, 2,6-divanillylidenecyclohexanone IV, and 2,7-bis(p-hydroxybenzylidene)cycloheptanone V at ambient temperature. These polyoxaloylesters were characterized by elemental analysis, IR spectra, ¹H NMR, solubility measurements, viscometry, DSC and thermogravimetric analyses. The crystallinity of the polymers was examined by x-ray analysis. The morphology of a high-performance polyoxaloylester, namely poly[oxyoxaloyloxy-p-phenylenemethylidyne (2-oxo-1,3-cyclohexanediylidene)methylidyne-p-phenylene], has been investigated by scanning electron microscopy. Electrical conductivity is in the range 10⁻¹¹ -10⁻¹³Ω⁻¹ cm⁻¹.

Six kinds of end-capped thermosetting copolyimides were prepared and applied as a junction coating resin for protection of semiconductor devices. The copolyimides are composed of aromatic dianhydrides, aromatic diamines, bis(γ-aminopropyl)tetramethyldisiloxane and reactive end-capping agents. Maleic anhydride and γ-aminopropyltrimethoxysilane were used as the reactive end-groups due to increasing their crosslinking reactivity. The copolyimides were cured at 200 °C, then the thermal and mechanical properties of the hardened copolyimides were characterized. The thermosetting copolyimides exhibited good adherence to a silicon wafer and an encapsulant without an adhesion promoter due to their incorporated disiloxane composition. The residual interface stress between the copolyimides and a silicon wafer was 3.5–3.6 MPa. The copolyimides were applied as a junction coating for protection of a semiconductor device and exhibited good reliability.

Poly(propylene imine)-based liquid crystalline dendrimers (PPILCDs) with a relatively flexible dendritic scaffold were successfully synthesized by reaction of poly(propylene imine) dendrimers with 4′-cyanobiphenyl hydrogen glutarate in the presence of condensing agent, diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate. The structures of PPILCDs were characterized by IR, ¹H NMR and MALDI-TOF mass spectroscopies and elemental analysis. These LCDs did not show a thermotropic liquid crystalline nature, but exhibited the liquid crystalline textures in the samples sheared at 70 °C. Furthermore, they showed a lyotropic liquid crystalline property in the 80 wt% DMF solutions.

A series of oligomeric azo dyes has been synthesized by coupling various aromatic diazonium salts to p-hydroxy benzoic acid–formaldehyde (p-HBAF) oligomer. They were evaluated in terms of their softening points, yields, colour, UV–visible spectra, IR spectra and PMR spectra. Dyeing on wool and nylon resulted in yellow to red shades having moderate to good fastness to light and good to very good fastness to washing.