Derek J. Irvine

Fire hazards and some common polymers

Abstract The annual fire statistics for the UK shows the pattern of injury and loss due to fire. Drawing on the current knowledge of fire safety engineering, the types of hazard commonly encountered in fires are described, including thermal parameters, smoke and toxic gas evolution. Fire tests based on established Standard tests measure only a limited range of material behaviours to a fire. Using the growing discipline of fire science, a better description of the intrinsic fire hazards for each material can be made. In a series of model calculations, some of the more commonly encountered polymers used in the construction industry are compared in their fundamental behaviour to fire using a fire science approach. From this, a simple ranking of material behaviour across a range of constant external heat fluxes can be made for each major fire hazard. The inclusion of data necessary for fire safety engineering to the growing number of polymer property databases is a readily available means to help promote fire safety through good engineering practice.

Evidence for the low thermal stability of poly(methyl methacrylate) polymer produced by atom transfer radical polymerisation

Abstract NMR spectroscopy confirmed the existence of a C–Br bond at the terminal chain end of low molecular weight poly(methyl methacrylate) (PMMA) produced by atom transfer radical polymerisation (ATRP). Polymer was prepared using the heterogeneous Cu(I)Br/2,2′-bipyridine (bpy) catalyst with ethyl-2-bromoisobutyrate used as the initiator. This structural feature was not evident in the matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry spectrum of the same polymer sample. The mass-to-charge ratios of the molecule ion peaks corresponded to a loss of methyl bromide (MeBr) from one chain end and concomitant cyclisation to give a lactone end group. Further information was obtained by means of matrix-assisted laser desorption/ionisation-collision induced dissociation (MALDI-CID) mass spectrometry. These spectra showed fragmentation patterns that were consistent with that shown previously for other alkyl methacrylate polymers. Evolved gas analysis detected the presence of MeBr in the volatiles collected when the polymer was heated from ambient temperature to 150°C. Furthermore, samples of PMMA, which had been previously heated to 150°C under an atmosphere of dinitrogen, were analysed by 13 C NMR. Spectra were similar to the samples that had not been heated apart from a complete loss of the C–Br resonance at δ 58xa0ppm and the appearance of other signals consistent with lactone formation. This was taken as evidence that PMMA terminated by a Br atom in this way, will undergo a thermal decomposition at ∼150°C that is similar to that observed in the MALDI experiments.

Self‐Optimizing Continuous Reactions in Supercritical Carbon Dioxide

Hands-free optimization: A combination of an automated flow reactor, online analysis, and a control algorithm leads to efficient optimization of reactions to a given product without the need for human intervention.

Cyclisation of dienes using phosphorus-centred radicals to form organophosphorus adducts

Abstract Reaction of various dienes with phosphites or related phosphorus hydrides, under free radical cyclisation conditions, affords cyclic organophosphorus adducts. This quick, mild and technically clean approach affords 5- and 6-ring carbocycles and heterocycles in good to excellent yield.

Preparation of cross-linked microparticles of poly(glycidyl methacrylate) by dispersion polymerization of glycidyl methacrylate using a PDMS macromonomer as stabilizer in supercritical carbon dioxide

Abstract This paper describes the dispersion polymerization of glycidyl methacrylate (GMA) employing poly(dimethylsiloxane) monomethacrylate as the stabilizer in supercritical carbon dioxide. Under the optimized conditions fine free flowing powder of discrete and cross-linked micropolymer particles are produced with high monomer conversion during a very short reaction time (

α,ω-dicarboxyl telechelic poly(methyl methacrylate) via radical addition-fragmentation polymerization

Abstract Catalytic chain transfer polymerization of benzyl methacrylate leads to a mixture of poly(benzyl methacrylate) macromonomers. Benzyl methacrylate dimer macromonomer has been isolated as a pure compound and used as a radical addition fragmentation chain transfer agent. This results in poly(methyl methacrylate) with both α and ω terminal benzyl methacrylate units. Catalytic hydrogenation of α,ω-benzyl methacrylate terminal poly(methyl methacrylate) results in evolution of toluene and formation of α,ω-dicarboxyl functional telechelic poly(methyl methacrylate). The products have been fully characterized by matrix-assisted laser desorption time-of-flight mass spectrometry in conjunction with 1H and 13C n.m.r. spectroscopy.

Transport and encapsulation of gold nanoparticles in carbon nanotubes.

Nanoparticles confined in small volumes exhibit functional properties different from that of the bulk material. Furthermore, the smaller the volume available then the greater the effects of confinement are observed to be. Metallic nanoparticles encapsulated within carbon nanotubes have been proposed for many applications ranging from catalysis to quantum storage devices. In this study we examine encapsulation of discrete gold nanoparticles (AuNP) within multi-wall carbon nanotubes (MWNT), with internal diameter less than 10 nm. During the encapsulation process AuNP undergo Ostwald ripening allowing them to reach a diameter that precisely matches the internal diameter of MWNT (snug fit). The use of supercritical CO2 as a processing medium enables efficient transport and irreversible encapsulation of AuNP into narrow nanotubes. Once inside MWNT, the nanoparticles are unable to grow further and retain their spheroidal shape. This dynamic behaviour observed for AuNP differs significantly from the behaviour of molecular guest-species under similar conditions.

Electromagnetic simulations of microwave heating experiments using reaction vessels made out of silicon carbide

There is a growing body of literature which reports the use of silicon carbide vessels to shield reaction mixtures during microwave heating. In this paper we use electromagnetic simulations and microwave experiments to show that silicon carbide vessels do not exclude the electric field, and that dielectric heating of reaction mixtures will take place in addition to heat transfer from the silicon carbide. The contribution of dielectric heating and heat transfer depends on the dielectric properties of the mixture, and the temperature at which the reaction is carried out. Solvents which remain microwave absorbent at high temperatures, such as ionic liquids, will heat under the direct influence of the electric field from 30-250 degrees C. Solvents which are less microwave absorbent at higher temperatures will be heated by heat-transfer only at temperatures in excess of 150 degrees C. The results presented in this paper suggest that the influence of the electric field cannot be neglected when interpreting microwave assisted synthesis experiments in silicon carbide vessels.

The homo and copolymerisation of 2-(dimethylamino)ethyl methacrylate in supercritical carbon dioxide

This paper describes the free radical dispersion homopolymerisation of 2-(dimethylamino) ethyl methacrylate (DMA) and copolymerisation of DMA with methyl methacrylate (MMA) in supercritical carbon dioxide (scCO2). The polymerisations are performed in the presence of two commercially available stabilisers, poly(dimethylsiloxane) monomethacrylate macromonomer (PDMS-mma) and the carboxylic acid terminated perfluoropolyether (Krytox 157FSL). Dry, fine powdered polymer product was produced for the copolymer under optimised conditions, but only aggregated solid is formed for homo poly(DMA). The effect of reaction time, stabiliser, copolymer composition and reaction pressure on the yield, molecular weight and morphology of the copolymers has been investigated. q 2003 Elsevier Science Ltd. All rights reserved.

Grafting polymers by enzymatic ring opening polymerisation—maximising the grafting efficiency

The synthesis of well-defined graft copolymers containing alkyl methacrylate, hydroxylalkyl methacrylate monomers and/or (poly(ethylene oxide) methacrylate macromonomers and their further graft chain extension with poly(e-caprolactone) (PCL) was studied in both conventional solvents and supercritical carbon dioxide (scCO2). A cascade two-step synthetic approach was adopted in which copolymer backbones were prepared in a first stage via atom transfer radical polymerisation (ATRP). These copolymers take the form of methacrylate based polymer backbones. In one case hydroxyl groups are pendant and close to the backbone (poly(MMA-co-HEMA)) whilst in the second, the hydroxyl groups are present as the terminal group of a poly(ethylene oxide) graft arm significantly separated from the main backbone (poly(MMA-co-PEGMA)). In stage two, these hydroxyl moieties were then used as the initiation centre for further chain extension via enzymatic ring opening polymerisation (eROP). These studies were designed to prepare different poly(alkyl methacrylate) copolymers by ATRP to optimise the grafting efficiency of the enzymatic polymerisation. We previously reported a limited grafting level of up to 40% for the pendant hydroxyl groups of a poly(MMA-co-HEMA) copolymer system. This study demonstrated that higher grafting efficiency (up to 80%) could be obtained by using a highly randomized MMA-co-HEMA polymeric backbone. By contrast, 100% grafting was achieved by moving the hydroxyl groups away from the backbone when using the longer hydroxyl-terminated poly(ethylene oxide) methacrylate monomer (PEGMA) as a co-monomer in poly(MMA-co-PEGMA) backbones.