55 research outputs found
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Healable polymeric materials: a tutorial review
Given the extensive use of polymers in the modern age with applications ranging from aerospace components to microcircuitry, the ability to regain the mechanical and physical characteristics of complex pristine materials after damage is an attractive proposition. This tutorial review focusses upon the key chemical concepts that have been successfully utilised in the design of healable polymeric materials
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Molecular recognition between functionalized gold nanoparticles and healable, supramolecular polymer blends â a route to property enhancement
A new, healable, supramolecular nanocomposite material has been developed and evaluated. The material comprises a blend of three components: a pyrene-functionalized polyamide, a polydiimide and pyrene- functionalized gold nanoparticles (P-AuNPs). The polymeric components interact by forming well-defined pâp stacked complexes between p-electron rich pyrenyl residues and p-electron deficient polydiimide residues. Solution studies in the mixed solvent chloroformâhexafluoroisopropanol (6 : 1, v/v) show that mixing the three components (each of which is soluble in isolation), results in the precipitation of a supramolecular, polymer nanocomposite network. The precipitate thus formed can be re-dissolved on heating, with the thermoreversible dissolution/precipitation procedure repeatable over at least 5 cycles. Robust, self-supporting composite films containing up to 15 wt% P-AuNPs could be cast from 2,2,2- trichloroethanol. Addition of as little as 1.25 wt% P-AuNPs resulted in significantly enhanced mechanical properties compared to the supramolecular blend without nanoparticles. The nanocomposites showed a linear increase in both tensile moduli and ultimate tensile strength with increasing P-AuNP content. All compositions up to 10 wt% P-AuNPs exhibited essentially quantitative healing efficiencies. Control experiments on an analogous nanocomposite material containing dodecylamine-functionalized AuNPs (5 wt%) exhibited a tensile modulus approximately half that of the corresponding nanocomposite that incorporated 5 wt% pyrene functionalized-AuNPs, clearly demonstrating the importance of the designed interactions between the gold filler and the supramolecular polymer matrix
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Fluoride degradable and thermally debondable polyurethane based adhesive
We report the one-pot, solvent free synthesis of a stimuli-responsive polyurethane (PU) adhesive. The hard domains within the supramolecular PU network contain a silyl protected phenol âdegradable unitâ (DU). The DU undergoes rapid decomposition (<30 minutes) upon treatment with fluoride ions which causes depolymerisation of the linear PU adhesive. The mechanism of depolymerisation was investigated in solution using 1H NMR spectroscopy by following the degradation of the polymer in the presence of tetra-butylammonium fluoride (TBAF). In the absence of fluoride ions, the material behaves as a typical thermoplastic adhesive, and underwent four adhesion/separation cycles without loss of strength. The fluoride initiated depolymerisation of the PU adhesive in the solution state was verified by GPC analysis, showing reduction in Mn from 26.1 kg molâ1 for the pristine PU to 6.2 kg molâ1 for the degraded material. Degradation studies on solid samples of the PU which had been immersed in acetone/TBAF solution for 30 minutes exhibited a 91% reduction in their modulus of toughness (from 27 to 2 MJ mâ3). Lap shear adhesion studies showed the fluoride responsive PU was an excellent material to join metallic, plastic, glass and wood surfaces. Pull adhesion tests confirmed that immersing the adhesive in TBAF/acetone solution resulted in a reduction in strength of up to 40% (from 160 N to 95 N at break) after drying
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Novel polyvinylpyrrolidones to improve delivery of poorly-water soluble drugs; from design to synthesis and evaluation
Polyvinylpyrrolidone is a widely used in tablet formulations with the linear form acting as a wetting agent and disintegrant whereas the cross-linked form is a super-disintegrant. We have previously reported that simply mixing the commercial cross-linked polymer with ibuprofen disrupted drug crystallinity with consequent improvements in drug dissolution behavior. In this study, we have designed and synthesized novel cross-linking agents containing a range of oligoether moieties which have then be polymerized with vinylpyrrolidone to generate a suite of novel excipients with enhanced hydrogen-bonding capabilities. The polymers have a porous surface and swell in most common solvents and in water; properties which suggest their value as disintegrants. The polymers were evaluated in simple physical mixtures with ibuprofen as a model poorly-water soluble drug. The results show that the novel PVPs induce the drug to become âX-ray amorphousâ, which increased dissolution to a greater extent than that seen with commercial cross-linked PVP. The polymers stabilize the amorphous drug with no evidence for recrystallization seen after 20 weeks storage
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Efficient access to conjugated 4,4â˛-bipyridinium oligomers using the Zincke reaction: Synthesis, spectroscopic and electrochemical properties
The cyclocondensation reaction between rigid, electron-rich aromatic diamines and 1,1â˛-bis(2,4-dinitrophenyl)-4,4â˛-bipyridinium (Zincke) salts has been harnessed to produce a series of conjugated oligomers containing up to twelve aromatic/heterocyclic residues. These oligomers exhibit discrete, multiple redox processes accompanied by dramatic changes in electronic absorption spectra
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Conjugated, rod-like viologen oligomers: correlation of oligomer length with conductivity and photoconductivity
An iterative synthesis has been used to produce conjugated, monodisperse, viologen-based aromatic oligomers containing up to 12 aromatic/heterocyclic rings. The methoxy-substituted oligomers were soluble in common organic solvents and could be processed by spin coating. The conductivities of the resulting films (30 to 221 nm thick) increased by more than an order of magnitude as the oligomer length increased from unimer (1, 2.20Ă10-11 S cm-1) through dimer (2) to trimer (3, 6.87Ă10-10 S cm-1). The bandgaps of the materials were estimated from the absorption spectra of these thin films. The longest oligomer, 3, exhibited a noticeably narrower bandgap (2.3 eV) than the shorter oligomers (1 and 2 both 2.7 eV). Oligomer 3 also showed photoconductivity under irradiation across a wide range of wavelengths in the visible spectral region. In conjunction with DFT calculations of these systems our results suggest that structurally related viologen-type oligomers may find use in optoelectronic devices
Synthesis and evaluation of a silver nanoparticle/polyurethane composite that exhibits antiviral activity against SARS-CoV-2
In this proof-of-concept study, we aim to produce a polyurethane (PU)-based composite that can reduce the amount of viable SARS-CoV-2 virus in contact with the surface of the polymeric film without further interventions such as manual cleaning. Current protocols for maintaining the hygiene of commonly used touchpoints (door handles, light switches, shop counters) typically rely on repeated washing with antimicrobial products. Since the start of the SARS-CoV-2 pandemic, frequent and costly surface sanitization by workers has become standard procedure in many public areas. Therefore, materials that can be retrofitted to touchpoints, yet inhibit pathogen growth for extended time periods are an important target. Herein, we design and synthesise the PU using a one-pot synthetic procedure on a multigram scale from commercial starting materials. The PU forms a robust composite thin film when loaded with 10 wt% silver nanoparticles (AgNPs). The addition of AgNPs increases the ultimate tensile strength, modules of toughness and modulus of elasticity at the cost of a reduced elongation at break when compared to the pristine PU. Comparative biological testing was carried out by the addition of pseudotyped virus (PV) bearing the SARS-CoV-2 beta (B.1.351) VOC spike protein onto the film surfaces of either the pristine PU or the PU nanocomposite. After 24 h without further human intervention the nanocomposite reduced the amount of viable virus by 67% (p = 0.0012) compared to the pristine PU treated under the same conditions. The significance of this reduction in viable virus load caused by our nanocomposite is that PUs form the basis of many commercial paints and coatings. Therefore, we envisage that this work will provide the basis for further progress towards producing a retrofittable surface that can be applied to a wide variety of common touchpoints
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Fluoride-responsive debond on demand adhesives: manipulating polymercrystallinity and hydrogen bonding to optimise adhesion strength at lowbonding temperatures
This paper reports the solvent-free synthesis of a series of sixfluoride responsive debond-on-demand poly-urethane (PU) adhesives that contain a silyl functionalised degradable unit (DU). To optimise the adhesionstrength and debonding nature of the adhesives, the chemical composition of the PUs was varied according tothe structure of the polyol or the diisocyanate component in the polymer mainchain.1H NMR spectroscopy wasused to study the depolymerisation behaviour in solution state. It showed thattetra-butylammoniumfluoride(TBAF) triggered the breakdown of the DU unit without fragmenting the polyol mainchain indiscriminately. Onexposure tofluoride ions, the PUs underwent depolymerisation with reductions in Mnranging from 64 to 90% asmeasured by GPC analysis. The morphology and thermal properties of the PUs were characterised by differentialscanning calorimetry (DSC), rheology and variable temperature (VT) SAXS/WAXS analysis. Each techniquedemonstrated the reversibility of the supramolecular polymer network under thermal stimuli. PUs containingpoly(butadiene) soft segments were amorphous with glass transition and viscoelastic transition temperaturesdependent on the nature of the soft segment and diisocyanate starting materials. The PU containing a polyestersoft segment exhibited a defined melting point at 49 °C. Mechanical stress-strain analysis of the series of PUsshowed each exhibited greater than 70% reduction in toughness after treatment with TBAF for 30 min as aconsequence of the chemo-responsive degradation of the polymer mainchain. The material featuring an ester-based polyol demonstrated excellent adhesion at bonding temperatures as low as 60 °C. Moreover, this materialcould be thermally rebonded if broken by force without loss in adhesion strength over three debond-rebondcycles. Lap shear adhesion tests showed a reduction in adhesive strength of approximately 40% (from 11.4 MPato 7.3 MPa) on exposure tofluoride ion
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Multivalency in healable supramolecular polymers: the effect of supramolecular cross-link density on the mechanical properties and healing of non- covalent polymer networks
Polymers with the ability to heal themselves could provide access to materials with extended lifetimes in a wide range of applications such as surface coatings, automotive components and aerospace composites. Here we describe the synthesis and characterisation of two novel, stimuli-responsive, supramolecular polymer blends based on p-electron-rich pyrenyl residues and p-electron-deficient, chain-folding aromatic diimides that interact through complementary pâp stacking interactions. Different degrees of supramolecular âcross-linkingâ were achieved by use of divalent or trivalent poly(ethylene glycol)-based polymers featuring pyrenyl end-groups, blended with a known diimideâether copolymer. The mechanical properties of the resulting polymer blends revealed that higher degrees of supramolecular âcross-link densityâ yield materials with enhanced mechanical properties, such as increased tensile modulus, modulus of toughness, elasticity and yield point. After a number of break/heal cycles, these materials were found to retain the characteristics of the pristine polymer blend, and this new approach thus offers a simple route to mechanically robust yet healable materials
Synthesis and biological evaluation of benzodiazepines containing a pentafluorosulfanyl group
The widely used pentafluorosulfanyl group (SF5) was deployed as a bioisosteric replacement for a chloro-group in the benzodiazepine diazepam (Valiumâ˘). Reaction of 2-amino-5-pentafluorosulfanyl-benzophenone with chloroacetyl chloride followed by hexamethylenetetramine, in the presence of ammonia, led to 7-sulfurpentafluoro-5-phenyl-1H-benzo[1,4]diazepin-2(3H)-one (2c). The latter was able to undergo a Pd-catalysed ortho-arylation, demonstrating that these highly fluorinated benzodiazepines can be further modified to form more complicated scaffolds. The replacement of Cl by the SF5 group, led to a loss of potency for potentiating GABAA receptor activation, most likely because of a lost ligand interaction with His102 in the GABAA receptor Îą subunit. Dedicated to Professor Jonathan Williams, an inspirational and humble pioneer, a colleague and mentor in chemistry
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