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The potential to replace shark-derived squalene in vaccine adjuvant applications with synthetic squalene/poly(isoprene) oligomers, synthesized by the controlled oligomerization of isoprene is demonstrated. Following on from our previous work regarding the synthesis of poly(isoprene) oligomers, we demonstrate the ability to tune the molecular weight of the synthetic poly(isoprene) material beyond that of natural squalene, while retaining a final backbone structure that contained a minimum of 75% of 1,4 addition product and an acceptable polydispersity. The synthesis was successfully scaled from the 2 g to the 40 g scale both in the bulk (i.e., solvent free) and with the aid of additional solvent by utilizing catalytic chain transfer polymerization (CCTP) as the control method, such that the target molecular weight, acceptable dispersity levels, and the desired level of 1,4 addition in the backbone structure and an acceptable yield (∼60%) are achieved. Moreover, the stability and in vitro bioactivity of nanoemulsion adjuvant formulations manufactured with the synthetic poly(isoprene) material are evaluated in comparison to emulsions made with shark-derived squalene. Emulsions containing the synthetic poly(isoprene) achieved smaller particle size and equivalent or enhanced bioactivity (stimulation of cytokine production in human whole blood) compared to corresponding shark squalene emulsions. However, as opposed to the shark squalene-based emulsions, the poly(isoprene) emulsions demonstrated reduced long-term size stability and induced hemolysis at high concentrations. Finally, we demonstrate that the synthetic oligomeric poly(isoprene) material could successfully be hydrogenated such that >95% of the double bonds were successfully removed to give a representative poly(isoprene)-derived squalane mimic.

This paper reports the first detailed study focussed upon identifying the influence that microwave heating (MWH) has upon the mechanic steps involved in the tin catalysed ring-opening of lactones such as ɛ-caprolactone (CL). Direct comparison of conventional (CH) and microwave (MWH) heated kinetic studies showed that a key factor in the reduction of the polymerisation cycle time with MWH was the elimination of the induction period associated with in situ catalyst manufacture and initiation. NMR studies demonstrated that the most significant mechanistic change contributing to the observed induction time reduction/elimination was faster initiation (i.e., reaction of the initiatior/catalyst complex with the first monomer unit). Consequently, analysis of the dielectric properties of the reaction components predicted that this MWH induced change was related to the selective volumetric heating of both the catalyst and the monomer. Furthermore, this indication of the greater significance of the initiation step in defining the length of the induction period suggests that this is the rate determining step of the process, whether conducted by CH or MWH. Increasing the catalyst concentration was demonstrated to produce significant reductions in reaction heat-up time and to induce a significant (up to 30 °C) overshoot in reaction mixture bulk temperature in with MWH only. Thus supporting the conclusion that selective heating of the organometallic species in the system contributes directly to differences in the reaction conditions and which need to be taken into account when drawing comparisons with CH systems. Consequently, both effects were concluded to be thermally generated from selective volumetric heating.

The synthesis of methyl methacrylate (MMA) oligomers by catalytic chain transfer polymerization (CCTP) is demonstrated to be significantly accelerated by the use of microwave heating. The CCTP reactions, which use a cobalt-based catalyst to very efficiently control the molecular weight of the final polymer, were conducted in both a conventional oil bath and a CEM Discover microwave reactor with a target set point of 80 °C. The required reaction time was shown to be reduced from 300 to 3 min, while also retaining control over the polymerization. Additionally, for the first time the bulk temperature of these catalyzed polymerizations was monitored in both heating methods by the use of internal optical fiber sensors. It was demonstrated that, to monitor the temperature of the reaction correctly, it is essential to use an optical fiber sensor rather than the external IR sensor supplied with the reactor. The acceleration in the synthesis during microwave heating was attributed to selective heating of the radic...

Studies into the phenomena that explain the dielectric properties of azo initiators (AMBN and V70) at high temperatures are reported in this paper. Previous studies have successfully related the variation in dielectric properties of these species below 110 °C to either phase changes or the thermal production of free radicals. In the latter case the marked increase in their response was attributed to the free radicals having more prominent dipoles than their initiator precursors. This study reports the results of experiments designed to explain their observed dielectric characteristics within the temperature range of 110–150 °C. At these elevated temperatures, the decomposition half-life of the initiators studied should be of the order of few seconds. However, in both this and the previous reports, the dielectric response is found to remain at a significant level for several hours. The two prime explanations for the unexpected duration of the increased dielectric properties are (i) the presence of microwav...

A facile and highly reproducible autopolymerization method, mediated by catalytic chain transfer, for the synthesis of hyperbranched materials with high alkene functional group density is reported....

Catalytic chain transfer polymerization has been successfully used to produce a range of methyl acrylate (MA) and butyl acrylate (BA) synthetic polymers of specific, targeted molecular weights, with polydispersity index values in the range of 2–4.5. The rheological properties of a subgroup of these synthetic binders consisting of four MA homo-polymers and one MA–BA co-polymer were then determined by means of oscillatory testing using a dynamic shear rheometer (DSR). The rheological tests consisted of a combination of stress/strain amplitude and frequency sweeps using a standard 8 mm diameter parallel plate testing geometry. The rheological parameters of phase angle and complex, storage and loss moduli were then shifted to form master curves at a reference temperature of 25 °C and isochronal plots at 0.1, 1 and 10 Hz. The rheological properties of the synthetic polymers were also compared to those of standard road pavement bitumens. The results show that it is possible to produce a range of synthetic polyacrylates with different rheological responses by altering the reactant type, reactant concentration and polymerization conditions to match the rheological properties of road bitumens. All the polyacrylate binders showed a similar rheological profile with a unique viscoelastic response as represented by the phase angle master curves together with an upper limiting stiffness and intermediate temperature/frequency ‘plateau’ region as shown in the complex modulus master curves. The results of the rheological examination of the binders showed that the key material property that influenced the performance of the polyacrylates in these specific application tests was glass transition temperature rather than molecular weight. Over this range of investigated molecular weights, it is the ratio between the two polymers which determines the glass transition and as such determines the material properties. These findings suggest that such sustainably sourced polyacrylate binders may allow for a move from petrochemical feed stocks to be made and allow for targeted road pavement design based on local climates, offering improved mechanical robustness.

For the first time, the response of 2,2'-azobis(2-methyl-butyronitrile) (AMBN) to microwave heating at 2.45 GHz was studied by measuring its dielectric properties as a function of temperature with the observed variations being attributed to the physical form of the initiator, the 1 h decomposition half-life temperature, and the relaxation frequency.

The first dedicated study investigating how the dielectric properties of free-radical initiators vary with both temperature and time is reported herein. The materials tested were chosen because they are standard initiators that are widely used by both industry and academia. Initially, each initiator was subjected to thermogravimetric analysis under the same temperature/time profiles, which reflects the mass lost from the materials when subjected to conventional heating. By comparing these data to the dielectric properties, we found that both the melting and decomposition points are directly related to large changes in the dielectric properties of the sample. We then used these data to investigate the likelihood of electromagnetic fields at microwave frequencies being capable of exerting an effect on the molecular decomposition of these initiating species, through a polarization−relaxation mechanism, and whether this effect could potentially alter the mechanistic pathways taken in free-radical polymerization chemistry. Finally, we considered whether direct molecular-based effects of electromagnetic fields at microwave frequencies on such initating species are responsible for the empirical observations related to polymerization that have been reported in the literature, such as rate and molecular-weight enhancements. Use Mobile Site Copyright © 2011 American Chemical Society

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.

This paper demonstrates that direct, “in situ” measurement of a reaction mixture using a coaxial probe technique can be used to accurately follow the progress of a chemical reaction. Such a system was shown to clearly indicate the presence/onset of and define the magnitude of key reaction parameters such as induction periods and end-points over a broad range of temperatures and viscosities. Thus it allowed the reaction to be conducted for the ideal time period, so maximising reactor through-put, energy efficiency and end product quality. Furthermore, by relating these ‘in situ’ measurements to a pre-prepared calibration curve, key experimentally achieved reaction rates could be determined. Finally, these continuously acquired, non-intrusive ‘in situ’ measurements were validated by comparison to conventional and industry accepted off-line measurement techniques.

Poly(isoprene) oligomers have been synthesised by the use of a range of controlled radical polymerisation techniques, including Catalytic Chain Transfer Polymerisation (CCTP), Reversible Addition Fragmentation Chain Transfer Polymerisation (RAFT), Atom Transfer Radical Polymerisation (ATRP) and Reverse Atom Transfer Radical Polymerisation (RATRP). The key molecular targets were (a) a low number average molecular weight equivalent to that of squalene and (b) a final backbone structure that contains a minimum of 75% of the 1,4 addition form of the isoprene monomer. These structural elements closely match those of the natural squalene which is the cosmetic/health care industry benchmark. CCTP and RAFT were successful in achieving the set targets via solution based polymerisation. The yields of oligomer from these techniques were approximately the same (∼42% from CCTP and ∼47% from RAFT), as were the Mns, (750 and 850 ± 220 g mol−1 respectively versus a GPC squalene target Mn of 570 g mol−1) and polydispersities (1.28 and 1.21 respectively versus a GPC squalene target of 1.02). The backbone structure of the materials produced by these techniques were shown to exceed the 75% 1,4 addition target. Therefore, both of these techniques have the potential to produce the target structures on a larger/commercial scale. However, the choice of initiator and/or RAFT agent was found to have a strong influence on the molecular weight obtained. The ATRP and RATRP techniques proved unable to demonstrate sufficient control over the polymerisation to produce the target oligomers under the reactions conditions applied whilst achieving acceptable yields (>40%).

Rotating frame nuclear Overhauser effect spectroscopy (ROESY) has been used to probe the chemical environment in dialkyl-imidazolium ionic liquids. A qualitative use of the distance dependence of the rotating frame Overhauser enhancement (ROE) has shown that reactants and intermediates have variable affinities for the distinct domains that are proposed within ionic liquids. A model system based on the free radical polymerisation of methyl methacrylate (MMA) has been developed to investigate any differing affinities, and to investigate the hypothesis that segregation of species between domains within the ionic liquid structure is contributory towards the generation of unexpectedly high rates of polymerisation and final polymer molecular weights.