Paul A. Gurr

From well defined star-microgels to highly ordered honeycomb films

Star-microgels were prepared in a two-step process known as the arm first approach by Atom Transfer Radical Polymerization (ATRP). Living linear poly(methyl methacrylate) (PMMA), with molecular weight (Mn) of 10000 and 20000, was reacted with ethylene glycol dimethacrylate (EGDMA) as crosslinker and varying amounts of methyl methacrylate (MMA) as spacer, under ATRP conditions, to produce star-microgels with Mn ranging from 0.3 × 106 to 1.0 × 106 and number of arms, n(arms) from 11 to 74. As Mn of the arm was increased, a decrease in molecular weight and in the number of arms in the microgel was observed. Star-microgels, with MMA spacer incorporated in the core, were found to have lower molecular weight and lower arm number. The microgels were used as precursors to form honeycomb films. The films were cast under conditions of high humidity which produces condensed water droplets which act as the template for a precipitating polymer. This is the first report of the use of well defined star-microgels to cast highly ordered porous films. It is shown that the pore diameters decrease with increasing number of PMMA arms and with increasing molecular weight of the star-microgel.

Soft polymeric nanoparticle additives for next generation gas separation membranes

This article highlights a new approach of fabricating a gas separation membrane through the addition of well-defined soft polymeric nanoparticles into the existing polymeric structure. Well-defined soft polymeric nanoparticles based on novel poly(ethylene glycol) (PEG) and poly(ethylene glycol)-b-poly(dimethylsiloxane) (PEG-b-PDMS) grafted star polymers were synthesized via atom transfer radical polymerization (ATRP) and the ‘core-first’ approach in high conversions and high yields. Thin film composite (TFC) membranes with selective layers prepared from commercially available poly(amide-b-ether) (Pebax® 2533) blended with a series of these PEG and PEG-b-PDMS nanoparticles are prepared. Their ability to selectively separate carbon dioxide (CO2) from nitrogen (N2) was studied at 35 °C and an upstream pressure of 3.4 bar. The fabricated TFC membranes exhibited greatly improved flux. These results demonstrate the ability of soft polymeric nanoparticles to form localized, high flux, CO2 permeable domains within a selective matrix, which in turn leads to an increase in the gas separation performance.

A novel cross-linked nano-coating for carbon dioxide capture

Ultra-thin (∼100 nm) films with uniform thicknesses can facilitate high CO2 permeation and are of potential technological significance for CO2 capture. Among many approaches for obtaining such materials, the recently developed continuous assembly of polymers (CAP) technology provides a robust process, allowing for the production of defect-free, cross-linked and surface-confined thin films with nanometer scale precision. Through utilization of this nanotechnology, we have constructed composite membranes containing cross-linked ultra-thin surface films. The membrane materials formed exhibited significantly high permeances as well as excellent gas separation selectivity.

Highly permeable membrane materials for CO2 capture

The release of large quantities of CO2 into the atmosphere has been linked to global warming and climate anomalies. Membrane processes offer a potentially viable energy-saving alternative for CO2 capture in comparison with conventional technologies such as amine absorption. However, gas separation membranes that are currently available have insufficiently high permeance (flux) for large scale applications such as the treatment of high volume flue gas with low concentration of CO2. Here we demonstrate a class of thin film composite (TFC) membranes, consisting of a high molecular weight amorphous poly(ethylene oxide)/poly(ether-block-amide) (HMA-PEO/Pebax® 2533) selective layer and a highly permeable polydimethylsiloxane (PDMS) intermediate layer which was pre-coated onto a polyacrylonitrile (PAN) microporous substrate. In contrast to the performance of conventional materials, the selective layer of TFC membranes shows super-permeable characteristics and outstanding CO2 separation performance. This unprecedented result arises from the introduction of HMA-PEOs into the Pebax® 2533 matrix, leading to high CO2 permeability and flux. These results provide an encouraging direction to further develop TFC membranes for efficient CO2 capture processes.

Peptide-Based Star Polymers: The Rising Star in Functional Polymers

Peptide-based star polymers show great potential as the next-generation of functional polymers due to their structure-related properties. The peptide component augments the polymer’s properties by introducing biocompatible and biodegradable segments, and enhancing their functionalities and structural ordering, which make peptide-based star polymers an attractive candidate in the field of nanomedicine. This article provides a brief summary of the recent developments of peptide-based star polymers synthesised from 2009 onwards. It is evident that the studies conducted so far have only started to uncover the true potential of what these polymers can achieve, and with continued research it is anticipated that peptide-based star polymers will be realised as versatile platforms applicable to broader fields of study, including drug delivery, tissue engineering, biocoatings, bioimaging, and self-directing templating agents.

The effect of soft nanoparticles morphologies on thin film composite membrane performance

Well-defined branched and densely cross-linked soft nanoparticles (SNPs) were synthesized and incorporated into a poly(ether-b-amide) (Pebax®) matrix to form the selective layer of thin film composite (TFC) membranes. The fabricated TFC membranes exhibited distinct gas separation abilities. These results reveal the effect of SNP morphologies on the membrane performance. This study may provide insights and novel strategies to fabricate highly permeable membrane materials for carbon dioxide (CO2) capture.

Influence of Polymer Elasticity on the Formation of Non-Cracking Honeycomb Films

Non-planar non-cracking honeycomb (HC) structures are prepared from star polymers with high glass transition temperatures (T(g) ) and relatively low Youngs moduli (E). This study demonstrates that the Youngs modulus of a polymer is a more important factor than the glass transition temperature for determining the occurrence of cracking during HC film formation on non-planar surfaces.

Honeycomb Films from Perfluoropolyether-Based Star and Micelle Architectures

A perfluoropolyether-b-poly(t-butyl acrylate) (PFPE-b-PtBA) block copolymer macroinitiator was used to prepare both core cross-linked star (CCS) polymers and micelles, whereby the outer shell and core, respectively, are comprised of fluorinated segments. The star polymer complete with PFPE outer shell was synthesised via atom transfer radical polymerisation (ATRP) and the arm-first approach, through cross-linking of the PFPE-b-PtBA macroinitiator with ethylene glycol diacrylate (EGDA). Alternatively, the PFPE-b-PtBA block copolymer could be self-assembled in benzene to form micelles with a PtBA shell and PFPE core. Both the micelle and CCS polymer were subsequently fabricated into non-cracking honeycomb (HC) patterned films on both planar and non-planar surfaces via the ‘Breath Figure’ (BF) technique using a static casting system.

Cyclodextrin-based supramolecular polymeric nanoparticles for next generation gas separation membranes

Cyclodextrin-based supramolecular assemblies derived from poly(dimethylsiloxane) (PDMS) functionalized polyrotaxanes (PRXs) were self-assembled into core–shell morphologies and used as soft nanoparticle (SNP) additives in the selective layer of thin film composite (TFC) membranes for the first time. Various weight percentages (wt%) of the PRX SNP additives were combined with Pebax® 2533 to form the selective layer, and the gas transport properties of the TFC membranes were studied in detail. Increasing the amount of PRX SNP additives led to a significant increase in CO2 permeance of the membranes, with only a slight decrease in the CO2/N2 selectivity, which was attributed to the dynamic nature (i.e., translational and rotational freedom) of the conjugated PDMS chains on the PRXs. In comparison, the performance of membranes prepared using a conventional analogue with fixed PDMS chains was inferior. The excellent gas transport properties observed for membranes are attributed to the novel self-assembly process of the dynamic PRX SNP additives; the sliding nature of the conjugated PDMS chains allow for increased exposure of the CO2-philic PEG backbone and increased size of the hydrophobic core leading to improved membrane selectivity and permeability. The effect of varying operating conditions (feed pressure and temperature) was also investigated and compared between the dynamic and fixed additive systems. Interesting trends were observed with the dynamic PRX system which diverges from conventional systems. This study opens up new avenues for CD-based supramolecular chemistry in the field of membrane technologies for gas separation.

Autophobicity-Driven Surface Segregation and Patterning of Core-Shell Microgel Nanoparticles

Core-shell microgel (CSMG) nanoparticles, also referred to as core-cross-linked star (CCS) polymers, can be envisaged as permanently cross-linked block copolymer micelles and, as such, afford novel opportunities for chemical functionalization, templating, and encapsulation. In this study, we explore the behavior of CSMG nanoparticles comprising a poly(methyl methacrylate) (PMMA) shell in molten PMMA thin films. Because of the autophobicity between the densely packed, short PMMA arms of the CSMG shell and the long PMMA chains in the matrix, the nanoparticles migrate to the film surface. They cannot, however, break through the surface because of the inherently high surface energy of PMMA. Similar thermal treatment of CSMG-containing PMMA thin films with a polystyrene (PS) capping layer replaces surface energy at the PMMA/air interface by interfacial energy at the PMMA/PS interface, which reduces the energy barrier by an order of magnitude, thereby permitting the nanoparticles to emerge out of the PMMA bulk. This nanoscale process is reversible and can be captured at intermediate degrees of completion. Moreover, it is fundamentally general and can be exploited as an alternative means by which to reversibly pattern or functionalize polymer surfaces for applications requiring responsive nanolithography.