David Lunn - Academia.edu (original) (raw)

Papers by David Lunn

Polymer Chemistry, 2017

We report a chain-end modification strategy for the quantitative conversion of thiol and thiocarb... more We report a chain-end modification strategy for the quantitative conversion of thiol and thiocarbonylthio functional groups to bromides under mild conditions.

Journal of the American Chemical Society, Apr 13, 2017

A highly efficient photomediated atom transfer radical polymerization protocol is reported for se... more A highly efficient photomediated atom transfer radical polymerization protocol is reported for semi-fluorinated acrylates and methacrylates. Use of the commercially available solvent, 2-trifluoromethyl-2-propanol, optimally balances monomer, polymer, and catalyst solubility while eliminating transesterification as a detrimental side reaction. In the presence of UV irradiation and ppm concentrations of copper(II) bromide and Me6-TREN (TREN = tris(2-aminoethyl amine)), semi-fluorinated monomers with side chains containing between three and 21 fluorine atoms readily polymerize under controlled conditions. The resulting polymers exhibit narrow molar mass distributions (Đ ≈ 1.1) and high end group fidelity, even at conversions greater than 95%. This level of control permits the in situ generation of chain-end functional homopolymers and diblock copolymers, providing facile access to semi-fluorinated macromolecules using a single methodology with unprecedented monomer scope. The results d...

Nature Chemistry, 2017

The capability to graft synthetic polymers onto the surfaces of live cells offers the potential t... more The capability to graft synthetic polymers onto the surfaces of live cells offers the potential to manipulate and control their phenotype and underlying cellular processes. Conventional grafting-to strategies for conjugating preformed polymers to cell surfaces are limited by low polymer grafting efficiency. Here we report an alternative grafting-from strategy for directly engineering the surfaces of live yeast and mammalian cells through cell surface-initiated controlled radical polymerization. By developing cytocompatible PET-RAFT (photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization), synthetic polymers with narrow polydispersity (Mw/Mn < 1.3) could be obtained at room temperature in 5 minutes. This polymerization strategy enables chain growth to be initiated directly from chain transfer agents anchored on the surface of live cells using either covalent attachment or non-covalent insertion, while maintaining high cell viability. Compared to conventional grafting-to approaches, these methods significantly improve the efficiency of grafting polymer chains and enable the active manipulation of cellular phenotypes.

Nature Communications, 2016

Anisotropic nanoparticles prepared from block copolymers are of growing importance as building bl... more Anisotropic nanoparticles prepared from block copolymers are of growing importance as building blocks for the creation of synthetic hierarchical materials. However, the assembly of these structural units is generally limited to the use of amphiphilic interactions. Here we report a simple, reversible coordination-driven hierarchical self-assembly strategy for the preparation of micron-scale fibres and macroscopic films based on monodisperse cylindrical block copolymer micelles. Coordination of Pd(0) metal centres to phosphine ligands immobilized within the soluble coronas of block copolymer micelles is found to induce intermicelle crosslinking, affording stable linear fibres comprised of micelle subunits in a staggered arrangement. The mean length of the fibres can be varied by altering the micelle concentration, reaction stoichiometry or aspect ratio of the micelle building blocks. Furthermore, the fibres aggregate on drying to form robust, self-supporting macroscopic micelle-based thin films with useful mechanical properties that are analogous to crosslinked polymer networks, but on a longer length scale.

Journal of the American Chemical Society, 2016

Cylindrical block copolymer micelles have shown considerable promise in various fields of biomedi... more Cylindrical block copolymer micelles have shown considerable promise in various fields of biomedical research. However, unlike spherical micelles and vesicles, control over their dimensions in biologically-relevant solvents has posed a key challenge that potentially limits in depth studies and their optimisation for applications. Here, we report the preparation of cylindrical micelles of length in the wide range of 40 nm-1.10 µm in aqueous media with narrow length distributions (length polydispersities < 1.10). In our approach, an amphiphilic linear-brush block copolymer, with high potential for functionalization, was synthesized based on poly(ferrocenyldimethylsilane)-b-poly(allyl glycidyl ether) (PFS-b-PAGE) decorated with triethylene glycol (TEG), abbreviated as PFS-b-(PEO-g-TEG). PFS-b-(PEO-g-TEG) cylindrical micelles of controlled length with low polydispersities were prepared in N,N-dimethylformamide using small seed initiators via living crystallization-driven self-assembly. Successful dispersion of these micelles into aqueous media was achieved by dialysis against deionized water. Furthermore, B-A-B amphiphilic triblock comicelles with PFS-b-poly(2vinylpyridine) (P2VP) as hydrophobic "B" blocks and hydrophilic PFS-b-(PEO-g-TEG) "A" segments were prepared and their hierarchical self-assembly in aqueous media studied. It was found that superstructures formed depend on the length of the hydrophobic blocks. Quaternization of P2VP was shown to cause the disassembly of the superstructures, resulting in the first examples of water-soluble cylindrical multi-block comicelles. We also demonstrate the ability of the triblock comicelles with quaternized terminal segments to complex DNA and, thus, to potentially function as gene vectors.

Nature communications, Jan 2, 2015

Although the solution self-assembly of block copolymers has enabled the fabrication of a broad ra... more Although the solution self-assembly of block copolymers has enabled the fabrication of a broad range of complex, functional nanostructures, their precise manipulation and patterning remain a key challenge. Here we demonstrate that spherical and linear supermicelles, supramolecular structures held together by non-covalent solvophobic and coordination interactions and formed by the hierarchical self-assembly of block copolymer micelle and block comicelle precursors, can be manipulated, transformed and patterned with mediation by dynamic holographic assembly (optical tweezers). This allows the creation of new and stable soft-matter superstructures far from equilibrium. For example, individual spherical supermicelles can be optically held in close proximity and photocrosslinked through controlled coronal chemistry to generate linear oligomeric arrays. The use of optical tweezers also enables the directed deposition and immobilization of supermicelles on surfaces, allowing the precise cr...

Chemical Science, 2015

The solution-phase self-assembly or “polymerization” of discrete colloidal building blocks, such ... more The solution-phase self-assembly or “polymerization” of discrete colloidal building blocks, such as “patchy” nanoparticles and multicompartment micelles, is attracting growing attention with respect to the creation of complex hierarchical materials.

Block copolymers (BCPs) with a short crystallizable poly(ferrocenyldimethylsilane) (PFS) core-for... more Block copolymers (BCPs) with a short crystallizable poly(ferrocenyldimethylsilane) (PFS) core-forming block self-assemble in selective solvents to afford cylindrical micelles, the ends of which are active to further growth via a process termed living crystallization-driven self-assembly (CDSA). We now report studies of the CDSA of a series of crystalline-brush BCPs with C 6 (BCP 6), C 12 (BCP 12), and C 18 (BCP 18) n-alkyl branches that were prepared by the thiol−ene functionalization of PFS-b-PMVS (PMVS = poly(methylvinylsiloxane)). Although the increased n-alkyl brush length of BCP 12 and BCP 18 hindered micelle growth, the increased intercoronal chain repulsion could be alleviated by their coassembly with linear PFS-b-PMVS. When the coassembly was initiated by short cylindrical seed micelles, monodisperse block comicelles of controllable length with "patchy" coronal nanodomains were accessible. TEM and AFM analysis of micelles prepared from BCP 18 and PFS-b-PMVS were found to provide complementary characterization in that the OsO 4-stained PMVS coronal domains were observed by TEM, whereas the brush block domains of BCP 18 (which displayed greater height) were detected by tapping mode AFM. The results showed that the coassembly afforded a gradient structure, with an initial bias for the growth of the linear BCP over that of the more sterically demanding brush BCP, which was gradually reversed as the linear material was consumed. This represents the first example of living gradient CDSA, a process reminiscent of a living covalent gradient copolymerization of two different monomers. Although other possible explanations exist, simulations based on a statistical model indicated that the coronal nanodomains detected likely result from a segmented, gradient comicelle architecture that arises as a consequence of: (i) different rates of addition of BCP unimer to the micelle termini, and (ii) a cumulative effect resulting from steric hindrance associated with the brush block.

Polymer Chemistry, 2013

ABSTRACT Various thiols were reacted with poly(ferrocenylmethylvinylsilane) (PFMVS) homopolymers ... more ABSTRACT Various thiols were reacted with poly(ferrocenylmethylvinylsilane) (PFMVS) homopolymers using the radical-mediated thiol–ene reaction with a view to preparing metallopolymers with diverse functional groups. Post-polymerization thiol–ene reactions on poly(ferrocenyldimethylsilane)-b-poly(ferrocenylmethylvinylsilane) (PFDMS-b-PFMVS) diblock copolymers with dodecanethiol and octadecanethiol afforded diblocks with a long hexane-soluble block and a short crystalline, hexane-insoluble PFDMS block. The thiol–ene reactions provided sufficient control to allow access to diblocks that were partially substituted, thus leaving vinyl groups that might subsequently be used for further post-polymerization reactions.

Nature Communications, 2014

Emerging strategies based on the self-assembly of block copolymers have recently enabled the bott... more Emerging strategies based on the self-assembly of block copolymers have recently enabled the bottom-up fabrication of nanostructured materials with spatially distinct functional regions. Concurrently, a drive for further miniaturization in applications such as optics, electronics and diagnostic technology has led to intense interest in nanomaterials with well-defined patterns of emission colour. Using a series of fluorescent block copolymers and the crystallization-driven living self-assembly approach, we herein describe the synthesis of multicompartment micelles in which the emission of each segment can be controlled to produce colours throughout the visible spectrum. This represents a bottom-up synthetic route to objects analogous to nanoscale pixels, into which complex patterns may be written. Because of their small size and high density of encoded information, these findings could lead to the development of new materials for applications in, for example, biological diagnostics, miniaturized display technology and the preparation of encoded nanomaterials with high data density.

Macromolecules, 2012

The solution self-assembly of block copolymers with a π-conjugated, crystalline, core-forming blo... more The solution self-assembly of block copolymers with a π-conjugated, crystalline, core-forming block represents a facile strategy toward the preparation of semiconducting nanowires with potential for high-tech applications. In this study, two asymmetric block copolymers based on regioregular poly(3-hexylthiophene) (P3HT) and poly(methyl methacrylate) (PMMA), namely P3HT 40-b-PMMA 520 (6a) and P3HT 40-b-PMMA 1100 (6b) (block ratios = 1:13 and 1:27.5, respectively) were prepared via atom transfer radical polymerization (ATRP) from a P3HT macroinitiator. The solution self-assembly of the P3HT-b-PMMA block copolymers was subsequently studied under a variety of experimental conditions. Short, fiber-like micelles resulted when THF (common solvent for P3HT and PMMA) solutions of the block copolymer were dialyzed against ethyl acetate and n-butyl acetate (selective solvents for PMMA). The electronic properties of the fiber-like micelles obtained coupled with wide-angle X-ray scattering studies confirmed that the cores of the aggregates were crystalline and suggested that growth occurs via a crystallization-driven pathway. The average lengths of fiber-like micelles were shown to increase relative to those obtained from dialysis versus the PMMA selective solvent, when THF was slowly evaporated from mixtures containing n-butyl acetate and P3HT-b-PMMA unimers, thereby limiting the rate of P3HT aggregation. Furthermore, the formation of only relatively short (mainly under 200 nm, always <1 μm) fiber-like micelles in these studies, even when the ratio of THF/alkyl acetate was controlled carefully via dialysis or evaporation, indicated that homogeneous nucleation of P3HT-b-PMMA block copolymers is relatively facile. This behavior differs significantly from that detected for other block copolymers such as polyferrocenylsilane-based materials that undergo crystallization-driven self-assembly to form cylinders with lengths of up to 10 μm under analogous conditions.

Macromolecules, 2013

ABSTRACT This paper reports a new synthetic strategy for the preparation of polyferrocenylsilane ... more ABSTRACT This paper reports a new synthetic strategy for the preparation of polyferrocenylsilane (PFS) block copolymers. The block copolymers were prepared by Cu-catalyzed alkyne/azide cycloaddition of two homopolymer precursors that allows access to new functional PFS block copolymers (e.g., polyferrocenylsilane-block-poly(N-isopropylacrylamide)) (PFS-b-PNIPAM)). Trimethylsilyl-protected, alkyne-terminated PFS homopolymer was first prepared via living anionic polymerization, terminating living PFS with commercially available 4-[(trimethylsilyl)ethynyl]benzaldehyde. Subsequent deprotection of the trimethylsilyl group with NaOMe yielded the ethynyl-terminated PFS (ω-alkyne-PFS). This method should be readily applicable to other polymers prepared by living anionic polymerization. Subsequently, non-PFS homopolymers containing a complementary “clickable” azide functional group were synthesized either by anionic polymerization, modification of a commercially available polymer, or atom transfer radical polymerization via two different approaches. In an azide postpolymerization modification approach, polystyrene (PS) and poly(methyl methacrylate) (PMMA) were functionalized by azide substitution of the terminal halide after ATRP. Alternatively, the azide moiety was incorporated into the ATRP initiator prior to polymerization, e.g., to give PNIPAM-N3 and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA-N3). Finally, the alkyne-terminated PFS segment and the azide functionalized counter block were coupled through the formation of a 1,2,3-triazole ring. In this report, PFS-b-PNIPAM, PFS-b-PDMAEMA, PFS-b-PS, PFS-b-PMMA, PFS-b-polydimethylsiloxane, and PFS-block-poly(ethylene oxide) have been synthesized via this convenient modular protocol in high yield and high purity.

Macromolecular Chemistry and Physics, 2013

Journal of the American Chemical Society, 2011

Solution self-assembly of the regioregular polythiophene-based block copolymer poly(3-hexylthioph... more Solution self-assembly of the regioregular polythiophene-based block copolymer poly(3-hexylthiophene)b-poly(dimethylsiloxane) yields cylindrical micelles with a crystalline P3HT core. Monodisperse nanocylinders of controlled length have been prepared via crystallization-driven self-assembly using seed micelles as initiators.

Journal of the American Chemical Society, 2014

Monodisperse fiber-like micelles with a crystalline π-conjugated polythiophene core with lengths ... more Monodisperse fiber-like micelles with a crystalline π-conjugated polythiophene core with lengths up to ca. 700 nm were successfully prepared from the diblock copolymer poly(3-hexylthiophene)-block-polystyrene using a one-dimensional self-seeding technique. Addition of a polythiophene block copolymer with a different corona-forming block to the resulting nanofibers led to the formation of segmented B-A-B triblock comicelles by crystallization-driven seeded growth. The key to these advances appears to be the formation of a relatively defect-free crystalline micelle core under the selfseeding conditions.

Chemistry - A European Journal, 2013

With the aim of accessing colloidally stable, fiberlike, π-conjugated nanostructures of controlle... more With the aim of accessing colloidally stable, fiberlike, π-conjugated nanostructures of controlled length, we have studied the solution self-assembly of two asymmetric crystalline-coil, regioregular poly(3-hexylthiophene)-b-poly(2-vinylpyridine) (P3HT-b-P2VP) diblock copolymers, P3HT23-b-P2VP115 (block ratio=1:5) and P3HT44-b-P2VP115 (block ratio=ca. 1:3). The self-assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu-catalyzed azide-alkyne cycloaddition reactions of azide-terminated P2VP and alkyne end-functionalized P3HT homopolymers. When the block copolymers were self-assembled in a solution of a 50% (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP-selective alcoholic solvent (MeOH&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;iPrOH&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;nBuOH). Very long (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain-extended P3HT blocks. The crystallinity and π-conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide-angle X-ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT23-b-P2VP115 resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT23-b-P2VP115 unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (L(w)/L(n) &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 1.11) and lengths from about 100-300 nm, that were dependent on the unimer-to-seed micelle ratio.