Brendan J. Howlin

Using Molecular Simulation to Predict the Physical and Mechanical Properties of Polybenzoxazines

Publisher Summary This chapter addresses the simulation of the structures and selected properties of a series of benzoxazine monomers and polymers that are the focus of several research programs. The synthetic routes by which the novel monomers are produced are already in the public domain, the commercial monomers that are examined were kindly supplied by Huntsman Advanced Materials and characterized, but used without further purification. It explores polymer chemistry, which is adept at producing a wide range of polymeric materials tailored to a variety of applications. Polymer modeling is the counter part of the modeling used on a daily basis in the pharmaceutical industry. The vast sums of money and time that have to be invested to get a new drug to market have stimulated the field of pharmaceutical modeling, with protein homology modeling, protein-ligand docking, and computational design of combinatorial libraries commonplace these days. This is interesting as the average protein is a polymer of up to 20 monomers (amino acids), whereas the average synthetic polymer contains maybe one or two monomers. Synthetic polymer modeling ought to be conceptually simpler than protein modeling but there is less research into its applications. Polymer modeling is rapidly advancing to the stage where the modeling is quicker than the synthesis, and so computational screening of new potential polymers can be carried out prior to synthesis for desired properties.

Studies of cure schedule and final property relationships of a commercial epoxy resin using modified imidazole curing agents

Abstract A commercial epoxy prepolymer (MY750) was cured with novel modified imidazole curing agents under both isothermal and dynamic scanning conditions. The thermal behaviour of the formulated mixtures was investigated using differential scanning calorimetry and thermogravimetric analysis, and glass transition temperature (Tg) values derived for polymers resulting from both cure schedules. Tg values and the thermal stability of polymers arising from the isothermal cure schedules were generally higher than those for the corresponding dynamic cure. For samples cured by the dynamic curing process, a lower heating rate resulted in higher Tg values and superior thermal stability. The same findings were obtained for samples cured by the isothermal curing process when the relatively low initial cure temperatures were optimal. The results of this study indicate that the initial and post-cure conditions may affect the final properties, and support the view that both the initial and post-cure schedules are of critical importance in governing the nature of the early network formation and the final network structure.

Metals and coordination compounds as modifiers for epoxy resins

This review concentrates on the use of metals in the formulation of epoxy resin systems and the effect that this has on the physical and mechanical properties of the polymer system. Epoxy resins are one of the most important higher performance polymer systems in use today, ranging from simple two-part adhesives and sports equipment to high-tech applications such as formula one racing cars and the aerospace industry. Epoxy resins are capable of undergoing homopolymerisation, although this process generally yields products with inadequate properties for high-tech applications. Consequently, in many cases catalysts, additives and co-curing-agents are formulated with the epoxy resin to significantly increase the storage stability, decrease the cure time and improve the final properties. The use of metals to formulate resin systems with excellent storage stability is discussed, along with the use of coordination compounds to improve cured resin properties such as fracture toughness, thermal stability and water absorption, etc.

Preparation and characterization of imidazole–metal complexes and evaluation of cured epoxy networks

A series of copper complexes of epoxy-imidazole adducts have been prepared and characterized by 1H nuclear magnetic resonance (NMR) spectroscopy. Differential scanning calorimetry (DSC) was employed to investigate the thermal behaviour of the curing agents and to investigate the medium-term storage stability of a one-pot composition of a commercial epoxy resin when mixed with the complexes. The cure onset temperatures of the mixtures containing copper complexes are ca. 20–50 °C higher than those of the parent epoxy-imidazole adducts and the decrease of cure onset temperatures in the early stages of storage (up to 100 h) is less. The latent nature and improved storage stability of mixtures containing the copper complex were clearly demonstrated and confirmed by the viscosity behaviour of the catalysed mixtures of the commercial epoxy resins MY720 and MY750. 1H NMR and electron paramagnetic resonance (EPR) spectroscopy were employed to monitor the thermal decomposition of the copper(II) complexes, which were found to decompose at 120–130 °C and exist in equilibrium. Glass fibre-reinforced composite samples were prepared using a commercial epoxy resin cured with the complexes and their physico-mechanical properties were evaluated.

Synthesis, structure, and spectroscopic and electrochromic properties of bis(phthalocyaninato)zirconium(IV)

The crystal structure of the title compound [Zr(pc)2] has been solved by X-ray diffraction techniques. The cell is triclinic, P; a= 13.410(2)A, b= 13.400(7)A, c= 16.340(11)A, α= 68.68(1)°, β= 65.92(1)°, γ= 74.74(1)°, R= 0.039 and R′= 0.058 for 6576 reflections. The infrared spectrum and details of the solvent dependence of the electronic absorption spectrum are also given. [Zr(pc)2] has the most distorted rings of all the metal bisphthalocyanines so far reported. The distortion is primarily caused by the Zr–N distances (average 2.30 A), which though long for such Zr bonding, are very small when compared to other M–N bonds in similar structures. Cyclic voltammograms of [Zr(pc)2] are presented and discussed. The distorted structure has a detrimental effect on the electrochromic properties of the molecule, aiding decomposition during oxidation.

The ene reaction between maleimides and allyl-substituted aromatics

Abstract The products from the ‘ene’ reaction between allyl-substituted aromatics and maleic anhydride, maleimide, N-phenylmaleimide and N-(4-phenoxyphenyl)maleimide have been isolated and characterised, and a semi-quantitative assessment of ene and enophile reactivities has been made. The reaction between N-phenylmaleimide and allylaromatics bearing a 1,3,5-triazine substituent has been investigated as a model for a proposed cyanate ester-bis-maleimide-allyl cyanate ester ter-polymerisation.

High temperature 1H NMR studies of epoxy cure: A neglected technique

SummaryBy reference to the reaction of a copper complex of phenyl glycidyl ether and 2-ethyl-4-methylimidazole, and Bisphenol A diglycidyl ether, 1H nuclear magnetic resonance spectroscopy at high temperature is shown to be an excellent and under-utilized method for measuring the degree of cure, enabling kinetic parameters to be obtained.

Development of quantitative structure property relationships for poly(arylene ether)s

The technique of quantitative structure-activity relationships (QSAR) is well accepted by the drug design community. The analogous technique of quantitative structure-property relationships (QSPR) has applications in the field of polymer chemistry. A variety of molecular modeling and molecular orbital techniques was used to find molecular descriptors that could be used to derive an empirical equation to describe the glass transition temperature of two related classes of poly(arylene ether)s. The derived equation was then used to predict the thermal characteristics of another polymer of the same type.

Molecular Insights of p47phox Phosphorylation Dynamics in the Regulation of NADPH Oxidase Activation and Superoxide Production

Background: p47phox is a regulatory subunit of NADPH oxidase, which produces superoxide. Results: We propose a molecular dynamics model of p47phox phosphorylation and assembly with p22phox in NADPH oxidase activation supported by biochemical experiments. Conclusion: Ser-379 phosphorylation in the C-terminal tail is a molecular switch in p47phox activation. Significance: This report provides novel structural and mechanistic information of p47phox activation. Phagocyte superoxide production by a multicomponent NADPH oxidase is important in host defense against microbial invasion. However inappropriate NADPH oxidase activation causes inflammation. Endothelial cells express NADPH oxidase and endothelial oxidative stress due to prolonged NADPH oxidase activation predisposes many diseases. Discovering the mechanism of NADPH oxidase activation is essential for developing novel treatment of these diseases. The p47phox is a key regulatory subunit of NADPH oxidase; however, due to the lack of full protein structural information, the mechanistic insight of p47phox phosphorylation in NADPH oxidase activation remains incomplete. Based on crystal structures of three functional domains, we generated a computational structural model of the full p47phox protein. Using a combination of in silico phosphorylation, molecular dynamics simulation and protein/protein docking, we discovered that the C-terminal tail of p47phox is critical for stabilizing its autoinhibited structure. Ser-379 phosphorylation disrupts H-bonds that link the C-terminal tail to the autoinhibitory region (AIR) and the tandem Src homology 3 (SH3) domains, allowing the AIR to undergo phosphorylation to expose the SH3 pocket for p22phox binding. These findings were confirmed by site-directed mutagenesis and gene transfection of p47phox−/− coronary microvascular cells. Compared with wild-type p47phox cDNA transfected cells, the single mutation of S379A completely blocked p47phox membrane translocation, binding to p22phox and endothelial O2⨪ production in response to acute stimulation of PKC. p47phox C-terminal tail plays a key role in stabilizing intramolecular interactions at rest. Ser-379 phosphorylation is a molecular switch which initiates p47phox conformational changes and NADPH oxidase-dependent superoxide production by cells.

The crystal structures of 2-(2′-pyridyl)phenyltellurium(II) bromide and of the inclusion compound bis[2-(2′-pyridyl)phenyltellurium(II) chloride]·p-ethoxyphenyl-mercury(II) chloride

Abstract In 2-(2′-pyridyl)phenyltellurium(II) bromide (1) the coordination about tellurium may be described as pseudo-trigonal bipyramidal wth bromine (TeBr = 2.707(11) A) and nitrogen (TeN) = 2.236(11) A) atoms occupying axial positions. The equatorial plane comprises a carbon atome (TeC = 2.111(6) A) and two lone pairs of electrons. There are no significant intermolecular interactions between the six independent molecules in the unit cell. Bis[2-2′-pyridyl)phenyltellurium(II) chloride]·p-ethoxy-phenylmercury(II) chloride (2) may be regarded as an “inclusion compound” obtained by replacement of two RTeX (X = Cl or Br) molecules by two p-ethoxyphenylmercury(II) chloride entities. There is approximately linear coordination about mercury (CHgCl = 179.2°(4), Hg-C = 2.044(14) and HgCl = 2.328(4) A) and 2-(2′-pyridyl)phenyltellurium(II) chloride, with a structure similar to that of (1) above (TeN = 2.2366(6), TeCl = 2.558(1), TeC = 2.080(25) A). There are no significant intermolecular contacts.