Exemplification of catalyst design for microwave selective heating and its application to efficient in situ catalyst synthesis

The use of dielectric spectroscopy to develop an underpinning understanding of the molecular transformations involved in achieving the successful, rapid in situ synthesis of a catalytic chain transfer polymerisation (CCTP) catalyst using microwave heating is reported. The hypothesis behind the molecular design of this catalyst, such that it was tailored towards the application of microwave heating (MWH), is discussed, reviewed relative to the empirically results and compared to the performance of a benchmark preformed catalyst. The overall number/type of function group present in the catalyst, the degree of flexibility exhibited by its organic ligand system and level of solvation achieved are shown to be key factors affecting the interaction between the catalyst and the applied microwave energy. Use of microwave heating leads to fast, in situ formation of the catalyst (less than 30 second) within the polymerisation mixture, rendering prepreparation steps unnecessary and ensuring it is generated prior to the polymerisation reaction commencing. The data also suggests catalysts’ synthesis is achieved at levels of microwave power as low as 5 Watts, further adding to the efficiency and sustainability of the method and presents a potentially enormous opportunity to intensify current industrial processes

Optimised use of dielectric spectroscopy at microwave frequencies for direct online monitoring of polymerisation reactions

This study reports the first use of dielectric spectroscopy over at a wide frequency range to monitor, in real time, the progress of a ring opening polymerisation. An open-ended coaxial line sensor was placed directly into the reaction medium of a polymerisation of ε-caprolactone and used to characterise the dielectric properties of the polymerisation mixture both ‘in-situ’ and with time at microwave frequencies. In addition to measurements obtained by the sensor, samples of the medium were extracted at various time points for off-line analysis, to confirm the level of conversion and polymer molecular weights that had been achieved. The results demonstrated that the dielectric properties values exhibited by the reaction medium with time could be correlated directly to the progress of the reaction. Thus, the experimental data allowed the construction of a calibration curve which could be used to predict the conversion of monomer to polymer at any given point of the reaction. The dielectric data permitted also the identification of key reaction parameters, such as the optimum point of termination for the reaction. Furthermore, the analysis of the dielectric data over a wide frequency spectrum enabled the identification of the most suitable frequencies for the practical operation of the sensor, in terms of linearity and sensitivity. This will enable the development of suitable instrumentation and an improved strategy for the online monitoring and control of a broad range of polymerisation reactions

Enhanced 'In-situ' catalysis via microwave selective heating: catalytic chain transfer polymerisation

An extremely facile, single stage, ‘in-situ’, Catalytic Chain Transfer Polymerisation (CCTP) process has been identified, where the optimal polymerisation process was shown to depend upon a combination of catalyst characteristics (i.e. solubility, sensitivity, activity) and the method of heating applied. In comparison to the current benchmark catalyst, the preparation of which is only about 40 % efficient, this represents a significant increase in waste prevention/atom efficiency and removes the need for organic solvent. It was also shown possible to significantly reduce the overall ‘in-situ’ reaction cycle time by adopting different processing strategies in order to minimise energy use. The application of microwave heating was demonstrated to overcome system diffusion/dilution issues and result in rapid, ‘in-situ’ catalyst formation. This allowed processing times to be minimised by enabling a critical concentration of the species susceptible to microwave selective heating to dominate the heat and mass transfer involved

Rapid turnover of T cells in acute infectious mononucleosis.

During acute infectious mononucleosis (AIM), large clones of Epstein-Barr virus-specific T lymphocytes are produced. To investigate the dynamics of clonal expansion, we measured cell proliferation during AIM using deuterated glucose to label DNA of dividing cells in vivo, analyzing cells according to CD4, CD8 and CD45 phenotype. The proportion of labeled CD8(+)CD45R0(+) T lymphocytes was dramatically increased in AIM subjects compared to controls (mean 17.5 versus 2.8%/day; p<0.005), indicating very rapid proliferation. Labeling was also increased in CD4(+)CD45R0(+) cells (7.1 versus 2.1%/day; p<0.01), but less so in CD45RA(+) cells. Mathematical modeling, accounting for death of labeled cells and changing pool sizes, gave estimated proliferation rates in CD8(+)CD45R0(+) cells of 11-130% of cells proliferating per day (mean 47%/day), equivalent to a doubling time of 1.5 days and an appearance rate in blood of about 5 x 10(9) cells/day (versus 7 x 10(7) cells/day in controls). Very rapid death rates were also observed amongst labeled cells (range 28-124, mean 57%/day),indicating very short survival times in the circulation. Thus, we have shown direct evidence for massive proliferation of CD8(+)CD45R0(+) T lymphocytes in AIM and demonstrated that rapid cell division continues concurrently with greatly accelerated rates of cell disappearance

Wet and dry flexural high cycle fatigue behaviour of fully bioresorbable glass fibre composites: in-situ polymerisation versus laminate stacking

Fully bioresorbable phosphate based glass fibre reinforced polycaprolactone (PCL/PGF) composites are potentially excellent candidates to address current issues experienced with use of metal implants for hard tissue repair, such as stress shielding effects. It is therefore essential to investigate these materials under representative loading cases and to understand their fatigue behaviour (wet and dry) in order to predict their lifetime in service and their likely mechanisms of failure. This paper investigated the dry and wet flexural fatigue behaviour of PCL/PGF composites with 35% and 50% fibre volume fraction (Vf). Significantly longer flexural fatigue life (p < 0.0001) and superior fatigue damage resistance were observed for In-situ Polymerised (ISP) composites as compared to the Laminate Stacking (LS) composites in both dry and wet conditions, indicating that the ISP promoted considerably stronger interfacial bonding than the LS. Immersion in fluid (wet) during the flexural fatigue tests resulted in significant reduction (p < 0.0001) in the composites fatigue life, earlier onset of fatigue damage and faster damage propagation. Regardless of testing conditions, increasing fibre content led to shorter fatigue life for the PCL/PGF composites. Meanwhile, immersion in degradation media caused softening of both LS and ISP composites during the fatigue tests, which led to a more ductile failure mode. Among all the composites that were investigated, ISP35 (35% Vf) composites maintained at least 50% of their initial stiffness at the end of fatigue tests in both conditions, which is comparable to the flexural properties of human cortical bones. Consequently, ISP composites with 35% Vf maintained at least 50% of its flexural properties after the fatigue failure, which the mechanical retentions were well matched with the properties of human cortical bones

Methodology for the synthesis of methacrylate monomers using designed single mode microwave applicators

© 2019 The Royal Society of Chemistry. A novel single-well prototype high throughput microwave reactor geometry has been produced and shown to be capable of synthesizing an array of non-commercially available methacrylate monomers. The reactor, which delivers the energy required via a dedicated coaxial line, has been shown experimentally to outperform other conventional/microwave formats. It is demonstrated to achieve significantly higher conversions than the alternative reactor types, whilst requiring (a) low levels of input power, (b) no additional energy for agitation/mass transfer, (c) no solvent and (d) no environmentally impacting thermos-fluids

Controlled polymerisation and purification of branched poly(lactic acid) surfactants in supercritical carbon dioxide

Product degradability, sustainability and low-toxicity are driving demand for the synthesis of biobased polymers and surfactants. Here we report the synthesis of novel surface active polymers using cyclic esters (D,L-lactide) and temperature sensitive polyols (D-sorbitol) as renewable building blocks. We highlight the modification of chain length and degree of branching to provide a route to tailoring the properties and application performance of these new compounds. High processing temperatures (≥180 °C) and harsh post-reaction treatments are often needed to remove residual monomer and catalysts and these can become barriers to creating materials based on renewable resources. Here we exploit supercritical carbon dioxide (scCO2) as a green solvent to overcome these challenges; significantly reducing reaction temperatures, targeting controlled molecular weights with narrow dispersities and reducing sideproduct formation. Additionally in the same pot, we can use supercritical extraction to purify the compounds and to efficiently remove unreacted reagents, which could be recovered and recycled. We believe that our approach to the production and purification of these novel branched poly(lactides) is a significant step towards the development of the next generation of biopolymers and green surfactants, combining both the use of bio-sourced raw materials and the potential to use sustainable, low energy processes and techniques

Preparation and characterization of composites using blends of divinylbenzene-based hyperbranched and linear functionalized polymers

In this study, hyperbranched polymers were explored as matrix modifiers to create E-glass fiber (GF) reinforced polymer composites with enhanced mechanical properties. Hyperbranched polymers have lower viscosities than their linear equivalents, potentially providing enhanced fiber wet out leading to improved stress transfer. Hyperbranched (HB), hydrogenated hyperbranched (H-HB), and linear functional (LF) divinyl benzene were blended with linear polystyrene (LP) to form a range of composite matrix formulations. Blends of the HB and LP polymers were used since the neat hyperbranched polymers alone proved to be highly brittle when formed into a film. A neat LP-GF composite was also prepared as control. Of the three matrix modifiers considered, only the H-HB provided an improvement in mechanical properties in comparison to LP-GF. With the addition of 10 and 20 wt% H-HB, respectively, the flexural modulus increased by 25% (p < 0.05) and 36% (p < 0.05) and flexural strength increased by 15% (p < 0.05) and 31% (p < 0.005). The enhanced mechanical properties were attributed to better fiber wetting along with crystallization observed with the addition of 20 wt% H-HB. The non-reactive ethyl (-CH2-CH3) chain end group of the macromolecular H-HB resulted in a plasticizing effect, which in turn improved its wettability. The LP:HB polymer blends, on the other hand, underwent crosslinking due to the presence of the vinyl (-CH-CH2) chain ends leading to poor wettability in comparison to the LP:H-HB and LP:LF blended films and hence lower mechanical properties

A Click Chemistry Strategy for the Synthesis of Efficient Photoinitiators for Two‐Photon Polymerization

It is reported that efficient photoinitiators, suitable for two‐photon polymerization, can be obtained using the copper catalyzed azide/alkyne cycloaddition reaction. This click chemistry strategy provides a modular approach to the assembly of photoinitiators that enables the rapid variation of key fragments to produce photoinitiators with desirable properties. To assess the performance of the first‐in‐class photoinitiators generated by this approach, a screening method is developed to enable the rapid determination of polymerization and damage thresholds in numerous photoresists during two‐photon polymerization. The degree of consumption of vinyl groups (DC) and homogeneity of the polymerization are further assessed by micro‐Raman spectroscopy. Finally, more complex structures are fabricated to demonstrate that the efficient two‐photon polymerization of stable 3D microarchitectures can be achieved using triazole‐based photoinitiators

Ring opening polymerisation of ɛ-caprolactone with novel microwave magnetic heating and cyto-compatible catalyst

We report on the ring-opening polymerization of ε-caprolactone incorporated with a magnetic susceptible catalyst, FeCl 3, via the use of microwave magnetic heating (HH) which primarily heats the bulk with a magnetic field (H-field) from an electromagnetic field (EMF). Such a process was compared to more commonly used heating methods, such as conventional heating (CH), i.e., oil bath, and microwave electric heating (EH), which is also referred to as microwave heating that primarily heats the bulk with an electric field (E-field). We identified that the catalyst is susceptible to both the E-field and H-field heating, and promoted the heating of the bulk. Which, we noticed such promotion was a lot more significant in the HH heating experiment. Further investigating the impact of such observed effects in the ROP of ε-caprolactone, we found that the HH experiments showed a more significant improvement in both the product Mwt and yield as the input power increased. However, when the catalyst concentration was reduced from 400:1 to 1600:1 (Monomer:Catalyst molar ratio), the observed differentiation in the Mwt and yield between the EH and the HH heating methods diminished, which we hypothesized to be due to the limited species available that were susceptible to microwave magnetic heating. But comparable product results between the HH and EH heating methods suggest that the HH heating method along with a magnetic susceptible catalyst could be an alternative solution to overcome the penetration depth problem associated with the EH heating methods. The cytotoxicity of the produced polymer was investigated to identify its potential application as biomaterials