Andrew M. Groth

Water as Solvent in Polyimide Synthesis: Thermoset and Thermoplastic Examples

A combination of increasingly stringent environmental legislation and economic competition is driving industrial processes further and further towards the three “E”s of chemical manufacture: economy, efficiency and environmental impact. In this paper, we present a novel aqueous method for the synthesis of polyimides. The products resulting from this process perform similarly, through both qualitative and quantitative comparisons, to those conventionally produced using high boiling dipolar aprotic solvent. This highly efficient one-pot method potentially provides economic advantage through low solvent cost and environmental impact benefit from the manageable aqueous waste.

Water as Solvent in Polyimide Synthesis II: Processable Aromatic Polyimides

Some representative thermal, chemical and mechanical characteristics of ‘commercial type’ polyimides are presented in this second paper in a series on using water as solvent in polyimide synthesis. The commercial types of polyimide that have been produced in this study are closely related to Kapton, Upilex R®, Upilex S®, Avimid N® and PMR-15. The chemical characterization of these materials using both nuclear magnetic resonance and Fourier Transform infrared indicate very pure and fully imidized products. The thermal and mechanical data from techniques such as thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical thermal analysis reveal properties that are at least, equivalent to their commercial counterparts. Some improvement in processability is noted in pure materials, mixtures and chemically modified analogues of these well known polyimides. In addition this highly efficient one-pot method potentially provides economic advantages through low solvent cost and environmental impact benefits.

Rheological Properties of a Particulate-Filled Polymeric Composite through Fused Deposition Process

This paper presents an investigation on rheological properties of a new ABS (acrylonitrile-butadiene-styrene)-Iron composite for application in Fused Deposition Modelling rapid prototyping process. Test samples of ABS-Iron composites have been made by controlled centrifugal mixing and thermal compounding through a single-screw extruder and compression moulding. Rheological characterization was conducted using a capillary rheometer by measuring pressure drop at the die while varying the extrusion speed. Apparent shear rate and shear stress as well as viscosity of the melts were calculated. Modulated differential-scanning calorimetry (MDSC) techniques were used in order to characterize viscoelastic properties of these newly developed composites materials. Non-Newtonian behaviour of the composite melt has shown to follow a cross model of shear thinning characteristics.

Water as Solvent in Polyimide Synthesis III: Towards the Synthesis of Polyamideimides

Four different approaches to the synthesis of polyamideimides, which employ aqueous imidization, were studied in order to assess the viability of their preparation in water. Building on previous studies of synthesizing polyimides in water both one- and two-step methods were explored. The first direct method for polyamideimide synthesis forms both the amide and imide linkages simultaneously and is limited to appropriately activated diamine monomers. The second direct method uses commercially sourced diaminobenzanilide with standard tetracarboxylic acids in an imidization step to give the polyamideimide. This method, demonstrates the viability of using amide-containing diamines in a polyimidization step to synthesize the desired polymer. The third and fourth methods are both two-step processes and use aqueous imidization to produce imide-containing monomers with either amine or carboxylic acid terminal functionality. This is followed by standard amidation to produce high-quality polyamideimides.

PMR Type Polyimides by Aqueous Cyclization Methods Chemistry

PMR-15 has long been the leading resin system for high performance composite applications requiring long-term use temperatures up to 300°C. A mixture of carboxylic esters and acids, aromatic diamine and norbornyl end caps capable of crosslinking by a reverse Diels—Alder mechanism in methanol is pre-pregged into cloth and under careful processing conditions produces high quality composite parts. Some problems with handling and processing remain in this commercial system and in an attempt to overcome these problems we have synthesized a series of fully cyclized PMR type prepolymers under aqueous imidization conditions. Their solubility and cure behavior have been determined with a view to producing resins that will form good quality, high performance composites. While resins with these characteristics have been obtained, the best of them utilize significant proportions of relatively expensive co-monomers. Almost all of the materials presented in this study have very high temperature stability and high glass transition temperatures, although no one system out performs PMR-15 on a monomer cost basis, the advantages of water as the synthesis solvent includes both its low cost and low toxicity and its ability to fully react the monomers to cyclic imide structures.

Fire Performance of Nylon Nanocomposites Fabricated by Melt Intercalation

This paper presents results of a study carried out to evaluate the effects of an organomodified nanoclay, either on its own or in combination with a polyimide, upon the fire performance of a commercially available nylon. The fire performance, as determined using cone calorimetry showed that up to 40% improvement in the peak heat release rate could be achieved at addition levels of only around 5wt% of nanoclay. The level of improvement was shown to be strongly dependent upon nanoscale dispersion with a more highly exfoliated morphology, as determined using transmission electron microscopy, which showed a greater reduction in the peak heat release rate compared to a more ordered intercalated structure. Investigation of the mechanism of fire retardancy showed that the reduction in the heat release rate is due to the nanoclay reinforcing the char layer which prevented combustible products from entering in to the gaseous phase. Generally, though, the time to ignition is unaffected by nanoclay additions. The addition of the polyimide to the nanoclay reinforced nylon was inconclusive showing little evidence of further improvements in fire performance.