T C Morton

Preparation and Characterization of Some Novel Bismaleimide Monomers and Polymers Based on Diaminobisimides

New bismaleimide monomers, based on pure diaminobismides (DABIs) have been synthesized. In a number of cases the bismaleimide of the 2:1 (amine/anhydride) DABI adduct has been isolated as a pure compound, but where the starting DABI consisted of a mix of imide oligomers of the diamine and dianhydride (2:1, 3:2 and higher) the corresponding bismaleimide product was found also to have a similar composition ratio. This has been confirmed in one example by separation of the oligomer mix and characterization of the components. The utility of the various bismaleimides as monomers in composite matrices has been assessed by cocuring with the common coreactant, 3,3′-diallylbisphenol A. The physical properties and thermal stability of neat resin samples and laminates are reported as well as some mechanical properties.

Important Factors Controlling Synthesis of Imides in Water

Four amine/anhydride models have been studied in order to understand the critical factors which control the synthesis of imides and polyimides in water. This synthesis method has been proposed recently as a convenient, environmentally friendly method of producing both thermosetting and thermoplastic polyimides. The key starting step in the synthesis is the formation of a salt/complex between the hydrolysed anhydride and the amine. The results from a combination of quantitative 1H NMR, HPLC and DSC analysis have shown that the reactions are reversible, and that the important factor in driving the reaction to completion in water is the insolubility of the imide product. Analysis of the precipitated imides shows them to be free of significant amounts of the considerably more water soluble amic acids (i.e. the uncyclized amide acids), which often contaminate imides made in conventional aprotic solvents. Of the models investigated, only the imidization of the second amino group in 2, 4, 6-trimethyl-1, 3-phenylene diamine (TMPDA) was subject to kinetic control. A general conclusion from these experiments is that where a different result is observed in water synthesis of imides compared with conventional aprotic solvent synthesis, it is likely to reflect the vastly different solvation powers of the two solvents rather than a difference in reaction mechanism.

Preparation and characterization of some new diaminobisimides

A series of stable diaminobisimides (DABIs) has been prepared as alternatives to simple aromatic diamines for use in the preparation of condensation polymers. These DABIs were prepared by reacting two moles of an aromatic diamine with one mole of a dianhydride under conditions that minimize side reactions and the formation of oligomers. In many cases, the pure DABI consisting of two moles of the diamine and one mole of the dianhydride (i.e. the 2:1 product) can be obtained free of oligomers (i.e. the 3:2, 4:3 etc products). The studies have shown that the major factor determining the yield and purity of a DABI is the extent of conjugation between the two amino groups in the starting diamine: to a lesser extent steric effects in the diamines also influence the product composition. The reaction conditions necessary to produce these new DABIs are described together with extensive characterization of these materials by FTIR, 1H and 13C NMR and gel permeation chromatography. The results indicate that pure DABIs are more manageable materials than the impure. insoluble materials previously described in the literature and can be used successfully to produce useful high-temperature stable polymers.

The Utility of 2-Naphthol Derivatives As Diels–Alder Based Co-Reactants for Bismaleimides

A number of 2-naphthols were found to undergo a Diels–Alder addition reaction with maleimides. This reaction can be used to bring about the cure of bismaleimides. The simplest co-reactant prepared in this work was 7-allyloxy-2-naphthol and satisfactory cures were obtained with appropriate bismaleimides. However, the laminate coupons made using this system had lower thermal stability than those of a comparable system using the commercial co-reactant Matrimid 5292B. The performance of this new chemistry was further tested by incorporating the naphthol/maleimide Diels–Alder addition structure into two other co-reactants. The most successful of these compounds (the diallyl ether of the adduct made from Diels–Alder addition of 2, 7-dihydroxynaphthalene and 4-hydroxyphenylmaleimide) produced cured neat resin samples having T gs 30 °C higher than those of a comparable system cured with the standard bismaleimide co-reactant (Matrimid B) and had slightly higher tensile strength and modulus than this system. The fact that these laminate coupons had better thermal performance than the system using commercial co-reactant showed that the presence of the Diels–Alder adduct structure in the resin backbone was not detrimental to the normal performance of ene cured bismaleimides. On the other hand the same structure incorporated into phenylethynyl end-capped resins was found to compromise its thermal stability.

Thermal stability predictions of polymeric composites: comparison of medium-term weight loss at 250C with a kinetic mapping procedure:

A comparative evaluation was carried out between two different accelerated thermal aging tests for estimating thermo-oxidative stability (Tos) in advanced composite materials as part of an effort to determine if either could be used as a fast but reliable predictive method for assessing new materials. One test (kinetic mapping) was based on data obtained from highly accelerated thermogravimetric analysis (TGAo) techniques commonly used in matrix polymer synthetic work, the other was based on weight loss during medium-term aging at temperatures closer to the use temperature, and well below Ta. No correlation was found between the two sets of results when the measurements were carried out on a number of commercial as well as some new experimental resin and composite samples. Reasons for the discrepancies are advanced.