Methacryloxyethyl phosphate-grafted expanded polytetrafluoroethylene membranes for biomedical applications

Expanded polytetrafluoroethylene (ePTFE) membranes were modified by graft copolymerization with methacryloxyethyl phosphate (MOEP) in methanol and 2-butanone (methyl ethyl ketone (MEK)) at ambient temperature using gamma irradiation. The effect of dose rate (0.46 and 4.6 kGyh(-1)), monomer concentration (1-40 %) and solvent were studied and the modified membranes were characterized by weight increase, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XPS was used to determine the % degree of surface coverage using the C-F (ePTFE membrane) and the C-C (MOEP graft copolymer) peaks. Grafting yield, as well as surface coverage, were found to increase with increasing monomer concentration and were significantly higher for samples grafted in MEK than in methanol solution. SEM images showed distinctly different surface morphologies for the membranes grafted in methanol (smooth) and MEK (globular), hence indicating phase separation of the homopolymer in MEK. We propose that in our system, the non-solvent properties of MEK for the homopolymer play a more important role than solvent chain transfer reactions in determining grafting outcomes. (c) 2005 Society of Chemical Industry.

RAFT-mediated emulsion polymerization of styrene using a non-ionic surfactant

We report the successful RAFT-mediated emulsion polymerization of styrene using a non-ionic surfactant (Brij98), the highly reactive 1-phenylethyl phenyldithioacetate (PEPDTA) RAFT agent, and water-soluble initiator ammonium persulfate (APS). The molar ratio of RAFT agent to APS was identical in all experiments. Most of the monomer was contained within the micelles, analogous to microemulsion or miniemulsion systems but without the need of shear, sonication, cosurfactant, or a hydrophobe. The number-average molecular weight increased with conversion and the polydispersity index was below 1.2. This ideal 'living' behavior was only found when molecular weights of 9000 and below were targeted. It was postulated that the rapid transportation of RAFT agent from the monomer swollen micelles to the growing particles was fast on the polymerization timescale, and most if not all the RAFT agent is consumed within the first 10% conversion. In addition, it was postulated that the high nucleation rate from the high rate of exit ( of the R radical from the RAFT agent) and high entry rate from water-phase radicals ( high APS concentration) reduced the effects of 'superswelling' and therefore a similar molar ratio of RAFT agent to monomer was maintained in all growing particles. The high polydispersity indexes found when targeting molecular weights greater than 9000 were postulated to be due to the lower nucleation rate from the lower weight fractions of both APS and RAFT agent. In these cases, 'superswelling' played a dominant role leading to a heterogeneous distribution of RAFT to monomer ratios among the particles nucleated at different times.

Synthesis and aggregation behavior of four-arm star amphiphilic block copolymers in water

We report the first synthesis of amphiphilic four-arm star diblock copolymers consisting of styrene (STY) and acrylic acid (AA) made using reversible addition-fragmentation chain transfer (RAFT; Z group approach with no star-star coupling). The polymerization proceeded in an ideal living manner. The size of the poly(AA(132)-STYm)(4) stars in DMF were small and close to 7 nm, suggesting no star aggregation. Slow addition of water (pH = 6.8) to this mixture resulted in aggregates of 15 stars per micelle with core-shell morphology. Calculations showed that the polyAA blocks were slightly extended with a shell thickness of 15 nm. Treatment of these micelles with piperidine to cleave the block arms from the core resulted in little or no change on micelle size or morphology, but the polyAA shell thickness was close to 29 nm (33 nm is the maximum at full extension) suggesting a release of entropy when the arms are detached from the core molecule. In this work we showed through the use of star amphiphilic polymers that the micelle size, aggregation number, and morphology could be controlled.

Design and application of nanoscale actuators using block-copolymers

Block copolymers are versatile designer macromolecules where a “bottom-up” approach can be used to create tailored materials with unique properties. These simple building blocks allow us to create actuators that convert energy from a variety of sources (such as chemical, electrical and heat) into mechanical energy. In this review we will discuss the advantages and potential pitfalls of using block copolymers to create actuators, putting emphasis on the ways in which these materials can be synthesised and processed. Particular attention will be given to the theoretical background of microphase separation and how the phase diagram can be used during the design process of actuators. Different types of actuation will be discussed throughout.

Poly(3-hexylthiophene) based block copolymers prepared by "click" chemistry

p-Conjugated block copolymers have been prepared from terminal azide functionalized polystyrenes (PS) and alkyne functionalized poly(3- hexylthiophene)s (P3HT) via a copper(I) catalyzed Huisgen [3 + 2] dipolar cycloaddition reaction. The functionalized a-azido-PS homopolymer was prepared by atom transfer radical polymerization from a specifically designed initiator bearing the azide function, whereas ?-ethynyl-P3HT and a,?-pentynyl-P3HT were synthesized by a modified Grignard metathesis polymerization using alkynyl Grignard derivatives. The electronic environment of the alkynyl end groups was shown to be decisive in determining triazole ring formation.

Living cationic polymerization of styrene monomers

This thesis describes an experimental investigation of synthesis of polystyrene under various polymerization conditions such as solvent polarity, temperature, initial concentrations of initiator, catalyst, monomer and added salts or co-catalyst, which was achieved using the living cationic polymerization technology in conjunction with gel permeation chromatography (GPC) and NMR spectroscopy. Polymerizations of styrene were conducted using 1-phenyl ethylchloride (1-PEC) as an initiator and tin tetrachloride (SnCI4) as a catalyst in the presence of tetra-n-Butylammonium chloride (nBu4NCI). Effects of solvent polarity varied by mixing dichloromethane (DCM) and less polar cyclohexane (C.hex), temperature, initial concentrations of SnC14, 1-PEC and nBu4NCI on the polymerizations were examined, and the conditions under which a living polymerization can be obtained were optimised as: [styrene]o ~ 0.75 - 2 M; [1-PEC]o ~ 0.005 - 0.05 M; [SnCI4Jo ~ 0.05 - 0.4 M; [nBu4NCIJo ~ 0.001 - 0.1 M; DCM/C.hex ~ 50/0 - 20/30 v/v; T ~ 0 to -45°C. Kinetic studies of styrene polymerization using the Omnifit sampling method showed that the number average molecular weight (Mn) of the polymers obtained increased in direct proportion to monomer conversion and agreed well with the theoretical Mn expected from the concentration ratios of monomer to initiator. The linearities of both the 1n([MJoI[M]) vs. time plot and the Mn vs. monomer conversion plot, and the narrow molecular weight distribution (MWD) measured using GPC demonstrated the livingness of the polymerizations, indicating the absence of irreversible termination and transfer within the lifetimes of the polymerizations. The proposed 'two species' propagation mechanism was found to apply for the styrene polymerization with 1-PEC/SnCI4 in the presence of nBu4NCl. The further kinetic experiments showed that living styrene polymerizations were achieved using the 1-PEC/SnCI4 initiating system in mixtures of DCM/C.hex 30/20 v/v at -15°C in the presence of various bromide salts, tetra-n-butylammonium bromide, tetra-n-pentylammonium bromide, tetra-n-heptylammonium bromide, and tetra-n-octylammonium bromide, respectively. The types of the bromide salts were found to have no significant effect on monomer conversion, Mn, polydispersity and initiation efficiency. Living polymerizations of styrene were also achieved using titanium tetrachloride (TiCI4) as a catalyst and 1-PEC as an initiator in the presence of a small amount of 2,6-di-tert-butylpyridine or pyridine instead of nBu4NCl. GPC analysis showed that the polymers obtained had narrow polydispersities (P.D. < 1.3), and the linearities of both the In([MJo/[MJ) vs. time plot and the Mn vs. monomer conversion plot demonstrated that the polymerizations are living, when the ratio of DCM and C.hex was less than 40 : 10 and the reaction temperature was not lower than -15°C. The reaction orders relative to TiCl4 and 1-PEC were estimated from the investigations into the rate of polymerization to be 2.56 and 1.0 respectively. lH and 13C NMR analysis of the resultant polystyrene would suggest the end-functionality of the product polymers is chlorine for all living polymerizations.

Functionalisation of ethylene-propylene rubber with glycidyl methacrylate in the presence of comonomer and in situ compatibilisation of PET/f-EPR blends

The main aim of this work was two fold, firstly to investigate the effect of a highly reactive comonomer, divinylbenzene (DVB), on the extent of melt grafting of glycidyl methacrylate (GMA) on ethylene-propylene rubber (EPR) using 2,5-dimethyl-2,5-bis-(tert-butyl peroxy) hexane (Trigon ox 101, Tl 01) as a free radical initiator, and to compare the results with a conventional grafting of the same monomer on EPR. To achieve this, the effect of processing conditions and chemical composition including the concentration of peroxide, GMA and DVB on the extent of grafting was investigated. The presence of the comonomer (DVB) in the grafting process resulted in a significant increase in the extent of the grafting using only a small concentration of peroxide. It was also found that the extent of grafting increased drastically with increasing the DVB concentration. Interestingly, in the comonomer system, the extent of the undesired side reaction, normally the homopolymerisation of GMA (polyGMA) was shown to have reduced tremendously and in most cases the level of polyGMA was immeasurable in the samples. Compared to a conventional EPR-g-GMACONV (in the absence of a comonomer), the presence of the comonomer DVB in the grafting system was shown to result in more branching and crosslinking (shown from an increase in melt flow index (MFI) and torque values) and this was paralleled by an increase in DVB concentration. In contrast, the extent of grafting in conventional system increased with increasing the peroxide concentration but the level of grafting was much lower than in the case of DVB. Homopolymerisation of GMA and excessive crosslinking of EPR became dominant at high peroxide concentration and this. reflects that the side reactions were favorable in the conventional grafting system. The second aim was to examine the effect of the in-situ functionalised EPR when used as a compatibiliser for binary blends. It was found that blending PET with functionalised EPR (ƒ-EPR) gave a significant improvement in terms of blend morphology as well as mechanical properties. The results showed clearly that, blending PET with ƒ-EPRDVB (prepared with DVB) was much more effective compared to the corresponding PET/ƒ-EPRCONV (without DVB) blends in which ƒ-EPRDVB having optimum grafting level of 2.1 wt% gave the most pronounced effect on the morphology and mechanical properties. On the other hand, blends of PET/ƒ-EPRDVB containing high GMA/DVB ratio was found to be unfavorable hence exhibited lower tensile properties and showed unfavorable morphology. The presence of high polyGMA concentration in ƒ-EPRCONV was found to create damaging effect on its morphology, hence resulting in reduced tensile properties (e.g. low elongation at break). However, the use of commercial terpolymers based on ethylene-methacrylate-glycidyl methacrylate (EM-GMA)or a copolymer of ethylene-glycidyl methacrylate (E-GMA) containing various GMA levels as compatibilisers in PET/EPR blends was found to be more efficient compared to PET/EPR/ƒ-EPR blends with the former blends showing finer morphology and high elongation at break. The high efficiency of the terpolymers or copolymers in compatibilising the PET/EPR blends is suggested to be partly, higher GMA content compared to the amount in ƒ-EPR and due to its low viscosity.

Controlled synthesis of poly(neopentyl p-styrene sulfonate) via reversible addition-fragmentation chain transfer polymerisation

The controlled synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) using RAFT polymerisation has been studied. Selected experimental conditions led to the production of PNSS with variable molecular weights and low dispersities (D{stroke}≤1.50). The controlled synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) using reversible addition-fragmentation chain transfer polymerisation has been studied under a wide range of experimental conditions. PNSS can be used as an organic-soluble, thermally labile precursor for industrially valuable poly(p-styrene sulfonate), widely employed in technologies such as ionic exchange membranes and organic electronics. The suitability of two different chain transfer agents, three solvents, three different monomer concentrations and two different temperatures for the polymerisation of neopentyl p-styrene sulfonate is discussed in terms of the kinetics of the process and characteristics of the final polymer. Production of PNSS with systematically variable molecular weights and low dispersities (D{stroke} ≤1.50 in all cases) has been achieved using 2-azidoethyl 2-(dodecylthiocarbonothioylthio)-2-methylpropionate in anisole at 75°C, with an initial monomer concentration of 4.0molL-1. Finally, a poly(neopentyl p-styrene sulfonate)-b-polybutadiene-b-poly(neopentyl p-styrene sulfonate) (PNSS-b-PBD-b-PNSS) triblock copolymer has been synthesised via azide-alkyne click chemistry. Moreover, subsequent thermolysis of the PNSS moieties generated poly(p-styrene sulfonate) end blocks. This strategy allows the fabrication of amphiphilic copolymer films from single organic solvents without the need for post-deposition chemical treatment.

Biomimetic synthetic lubricants (Biosurfactants)

Poly(styrene-co-maleic anhydride) (PSMA) based copolymers are known to undergo conformational transition in response to environmental stimuli. This smart behaviour makes it possible to mimic the behaviour of native apoproteins. The primary aim of this study was to develop a better understanding of the structure-property relationships of various PSMA-based copolymers sought. The work undertaken in this thesis has revealed that the responsive behaviour of PSMA-based copolymers can be tailored by varying the molecular weight, hydrophobic (styrene) and hydrophilic (maleic acid) balance, and more so in the presence of additional hydrophobic, mono-partial ester moieties. Novel hydrophilic and hydrophobic synthetic surfactant protein analogues have successfully been prepared. These novel lipid solubilising agents possess a broad range of HLB (hydrophilic-lipophilic balance) values that have been estimated. NMR spectroscopy was utilised to confirm the structures for PSMA-based copolymers sought and proved useful in furthering understanding of the structure-property relationships of PSMA-based copolymers. The association of PSMA with the polar phospholipid, 2-dilauryl-sn-glycero-3- phosphocholine (DLPC) produces polymer-lipid complexes analogous to lipoprotein assemblies present in the blood plasma. NMR analysis reveals that the PSMA-based copolymers are not perfectly alternating. Regio-irregular structures, atactic and random monomer sequence distribution have been identified for all materials studied. Novel lipid solubilising agents (polyanionic surfactants) have successfully been synthesised from a broad range of PSMA-based copolymers with desired estimated HLB values that interact with polar phospholipids (DLPC/DPPC) uniquely. Very low static and dynamic surface tensions have been observed via the du Noϋy ring method and Langmuir techniques and correlate well with the estimated HLB values. Synthetic protein-lipid analogues have been successfully synthesised, that mimic the unique surface properties of native biological lubricants without the use of solvents. The novel PSMA-DLPC complexes have successfully been combined with hyaluronan (hyaluronic acid, HA). Today, the employment of HA is economically feasible, because it is readily available from bacterial fermentation processes in a thermally stable form - HyaCare®. The work undertaken in this thesis highlights the usage of HA in biolubrication applications and how this can be optimised and thus justified by carefully selecting the biological source, concentration, molecular weight, purity and most importantly by combining it with compatible boundary lubricating agents (polar phospholipids). Experimental evidence supports the belief that the combined HA and PSMA-DLPC complexes provide a balance of rheological, biotribological and surface properties that are composition dependent, and show competitive advantage as novel synthetic biological lubricants (biosurfactants).

GPCR-styrene maleic acid lipid particles (GPCR-SMALPs):their nature and potential

G-protein-coupled receptors (GPCRs) form the largest class of membrane proteins and are an important target for therapeutic drugs. These receptors are highly dynamic proteins sampling a range of conformational states in order to fulfil their complex signalling roles. In order to fully understand GPCR signalling mechanisms it is necessary to extract the receptor protein out of the plasma membrane. Historically this has universally required detergents which inadvertently strip away the annulus of lipid in close association with the receptor and disrupt lateral pressure exerted by the bilayer. Detergent-solubilized GPCRs are very unstable which presents a serious hurdle to characterization by biophysical methods. A range of strategies have been developed to ameliorate the detrimental effect of removing the receptor from the membrane including amphipols and reconstitution into nanodics stabilized by membrane scaffolding proteins (MSPs) but they all require exposure to detergent. Poly(styrene-co-maleic acid) (SMA) incorporates into membranes and spontaneously forms nanoscale poly(styrene-co-maleic acid) lipid particles (SMALPs), effectively acting like a 'molecular pastry cutter' to 'solubilize' GPCRs in the complete absence of detergent at any stage and with preservation of the native annular lipid throughout the process. GPCR-SMALPs have similar pharmacological properties to membrane-bound receptor, exhibit enhanced stability compared with detergent-solubilized receptors and being non-proteinaceous in nature, are fully compatible with downstream biophysical analysis of the encapsulated GPCR.

Application of staged O2 feeding in the oxidative dehydrogenation of ethylbenzene to styrene over Al2O3 and P2O5/SiO2 catalysts

Drastic improvements in styrene yield and selectivity were achieved in the oxidative dehydrogenation of ethylbenzene by staged feeding of O2. Six isothermal packed bed reactors were used in series with intermediate feeding of O2, while all EB was fed to the first reactor, diluted with helium or CO2 (1:5 molar ratio), resulting in total O2:EB molar feed ratios of 0.2-0.6. The two catalyst samples, γ-Al 2O3 and 5P/SiO2, that were applied both benefitted from this operation mode. The ethylbenzene conversion per stage and the selectivity to styrene were significantly improved. The production of COX was effectively reduced, while the selectivity to other side products remained unchanged. Compared with co-feeding at a total O 2:EB molar feed ratio of 0.6, by staged feeding the EB conversion (+15% points for both catalysts), ST selectivity (+4% points for both samples) and O2 (ST) selectivity (+9% points for γ-Al2O 3 and +17% points for 5P/SiO2) all improved. The ethylbenzene conversion over 5P/SiO2 can be increased from 18% to 70% by increasing the number of reactors from 1 to 6 with each reactor a total amount of O2 of 0.1 without the loss of ST selectivity (93%). For 5P/SiO2 a higher temperature (500 C vs. 450 C for Al 2O3) is required. Essentially more catalyst (5P/SiO 2) was required to achieve full O2 conversion in each reactor. Staged feeding of O2 does not eliminate the existing issues of the catalyst stability both in time-on stream and as a function of the number of catalyst regenerations (5P/SiO2), or the relatively moderate performance (relatively low styrene selectivity for γ-Al2O 3). © 2014 Elsevier B.V.

Oxidative dehydrogenation of ethylbenzene to styrene over alumina:effect of calcination

Commercially available γ-Al2O3 was calcined at temperatures between 500 and 1200 °C and tested for its performance in the oxidative ethylbenzene dehydrogenation (ODH) over a wide range of industrially-relevant conditions. The original γ-Al2O 3, as well as η- and α-Al2O3, were tested. A calcination temperature around 1000/1050 °C turned out to be optimal for the ODH performance. Upon calcination the number of acid sites (from 637 to 436 μmol g-1) and surface area (from 272 to 119 m 2 g-1) decrease, whereas the acid site density increases (from 1.4 to 2.4 sites per nm2). Less coke, being the active catalyst, is formed during ODH on the Al-1000 sample compared to γ-Al 2O3 (30.8 wt% vs. 21.6 wt%), but the coke surface coverage increases. Compared with γ-Al2O3, the EB conversion increased from 36% to 42% and the ST selectivity increased from 83% to 87%. For an optimal ST selectivity the catalyst should contain enough coke to attain full conversion of the limiting reactant oxygen. The reactivity of the coke is changed due to the higher density and strength of the Lewis acid sites that are formed by the high temperature calcination. The Al-1000 sample and all other investigated catalysts lost ODH activity with time on stream. The loss of selectivity towards more COX formation is directly correlated with the amount of coke. © The Royal Society of Chemistry 2013.

Membrane protein extraction and purification using styrene-maleic acid (SMA) co-polymer:effect of variations in polymer structure

The use of styrene maleic acid (SMA) co-polymers to extract and purify transmembrane proteins, whilst retaining their native bilayer environment, overcomes many of the disadvantages associated with conventional detergent based procedures. This approach has huge potential for the future of membrane protein structural and functional studies. In this investigation we have systematically tested a range of commercially available SMA polymers, varying in both the ratio of styrene to maleic acid and in total size, for the ability to extract, purify and stabilise transmembrane proteins. Three different membrane proteins (BmrA, LeuT and ZipA) which vary in size and shape were used. Our results show that several polymers can be used to extract membrane proteins comparably to conventional detergents. A styrene:maleic acid ratio of either 2:1 or 3:1, combined with a relatively small average molecular weight (7.5-10 kDa) is optimal for membrane extraction, and this appears to be independent of the protein size, shape or expression system. A subset of polymers were taken forward for purification, functional and stability tests. Following a one-step affinity purification SMA 2000 was found to be the best choice for yield, purity and function. However the other polymers offer subtle differences in size and sensitivity to divalent cations that may be useful for a variety of downstream applications.

Study of the kinetics and mechanism of rapid self-assembly in block copolymer thin films during solvo-microwave annealing

Microwave annealing is an emerging technique for achieving ordered patterns of block copolymer films on substrates. Little is understood about the mechanisms of microphase separation during the microwave annealing process and how it promotes the microphase separation of the blocks. Here, we use controlled power microwave irradiation in the presence of tetrahydrofuran (THF) solvent, to achieve lateral microphase separation in high- lamellar-forming poly(styrene-b-lactic acid) PS-b-PLA. A highly ordered line pattern was formed within seconds on silicon, germanium and silicon on insulator (SOI) substrates. In-situ temperature measurement of the silicon substrate coupled to condition changes during "solvo-microwave" annealing allowed understanding of the processes to be attained. Our results suggest that the substrate has little effect on the ordering process and is essentially microwave transparent but rather, it is direct heating of the polar THF molecules that causes microphase separation. It is postulated that the rapid interaction of THF with microwaves and the resultant temperature increase to 55 degrees C within seconds causes an increase of the vapor pressure of the solvent from 19.8 to 70 kPa. This enriched vapor environment increases the plasticity of both PS and PLA chains and leads to the fast self-assembly kinetics. Comparing the patterns formed on silicon, germanium and silicon on insulator (SOI) and also an in situ temperature measurement of silicon in the oven confirms the significance of the solvent over the role of substrate heating during "solvo-microwave" annealing. Besides the short annealing time which has technological importance, the coherence length is on a micron scale and dewetting is not observed after annealing. The etched pattern (PLA was removed by an Ar/O-2 reactive ion etch) was transferred to the underlying silicon substrate fabricating sub-20 nm silicon nanowires over large areas demonstrating that the morphology is consistent both across and through the film.