MaDDOSY (Mass Determination Diffusion Ordered Spectroscopy) using an 80 MHz Bench Top NMR for the Rapid Determination of Polymer and Macromolecular Molecular Weight.

Measurement of molecular weight is an integral part of macromolecular and polymer characterization which usually has limitations. Herein, this article presents the use of a bench-top 80 MHz Nuclear Magnetic Resonance (NMR) spectrometer for diffusion-ordered spectroscopy as a practical and rapid approach for the determination of molecular weight/size using a novel solvent and polymer-independent universal calibration.

Lewis acid catalysed polymerisation of cyclopentenone.

A modest structural change of a ß-diketiminate-supported aluminium complex leads to dramatic differences in the reactivity towards cyclopentenone. While the bulkier complex efficiently executes Diels Alder transformations the smaller analogue performs unique polymerisation of this substrate. This observation appears to be unprecedented in the chemistry of Lewis acids and cyclic dienophiles as it represents a unique way to polymerise a functionalised olefin.

Process intensification of continuous-flow seATRP by a sonicated multi-reactor setup.

Simplified electrochemically mediated atom transfer radical polymerization (seATRP) is a versatile technique for synthesizing polymers with precise control and complex architecture. Continuous-flow seATRP has recently been realized by using a sonicated microreactor but still faces limitations such as relatively low conversion and difficulties in synthesizing polymers with high molecular weight. Herein, a novel multi-reactor setup is demonstrated. By tuning the currents applied to different reaction stages in the setup, 90% conversion can be achieved while maintaining relatively low dispersity (<1.35). Meanwhile, the unique design enables a wider processing window for sonication due to greater viscous attenuation in the second reactor, thus largely addressing the problem associated with high viscosity during the synthesis of high molecular weight polymers. The developed setup also offers an alternative strategy for future scale-up of continuous-flow seATRP.

From monomer to micelle: a facile approach to the multi-step synthesis of block copolymers via inline purification.

A one-pass continuous flow strategy to form block copolymer nanoaggregates directly from monomers is presented. A key development towards such a sophisticated continuous flow setup is a significant improvement in continuous flow dialysis. Often impurities or solvent residues from polymerizations must be removed before block extensions or nanoaggregate formation can be carried out, typically disrupting the workflow. Hence, inline purification systems are required for fully continuous operation and eventual high throughput operation. An inline dialysis purification system is developed and exemplified for amphiphilic block copolymer synthesis from thermal and photoiniferter reversible addition fragmentation chain transfer (RAFT) polymerization. The inline dialysis system is found to be significantly faster than conventional batch dialysis and the kinetics are found to be very predictable with a diffusion velocity coefficient of 4.1 × 10-4 s-1. This is at least 4-5 times faster than conventional dialysis. Moreover, the newly developed setup uses only 57 mL of solvent for purification per gram of polymer, again reducing the required amount by almost an order of magnitude compared to conventional methods. Methyl methacrylate (MMA) or butyl acrylate (BA) was polymerized in a traditional flow reactor as the first block via RAFT polymerization, followed by a 'dialysis loop', which contains a custom-built inline dialysis device. Clearance of residual monomers is monitored via in-line NMR. The purified reaction mixture can then be chain extended in a second reactor stage to obtain block copolymers using poly(ethylene glycol) methyl ether acrylate (PEGMEA) as the second monomer. In the last step, nano-objects are created, again from flow processes. The process is highly tuneable, showing for the chosen model system a variation in nanoaggregate size from 34 nm to 188 nm.

High Throughput Multidimensional Kinetic Screening in Continuous Flow Reactors.

An automated high throughput multidimensional reaction screening platform based on an inline Fourier-transform infrared spectroscopy is presented. By combining flow chemistry, machine automation and inline analysis, the platform is able to screen reactions in multidimensions (residence time, monomer concentration, degree of polymerization, reaction temperature and monomer conversion) rapidly and efficiently way. Kinetic data libraries associated with high data precision (absolute error <4 %), high reproducibility and high data density are built with ease from the platform. To test the method, we screened the reversible addition-fragmentation chain transfer polymerization of methyl acrylate in unmatched detail, and the ring opening metathesis polymerization of methyl-5-norbornene-2-carboxylate. The method we introduce is a key step in providing "big data" for data driven research in the future, and already at present allows for precise prediction of reaction outcomes within the high-dimensional chemical parameter space that is screened.

Photoresponsive Emulsion-Templated Porous Materials via Orthogonal Photoclick Chemistry.

The functionalization of emulsion-templated porous polymers (polyHIPEs) utilizing modern and efficient chemistries is an important avenue for tailoring the properties of these scaffolds for specific and specialized applications. Herein, tetrazole photoclick chemistry is utilized for the efficient functionalization of polyHIPEs synthesized from various monomer systems and polymerization chemistries. Using both radical polymerization and thiol-ene polymerization, polyHIPEs with well-defined, interconnected open-cell morphologies are synthesized with tetrazole concentrations ranging from 0 to 5 w/v %, with the pore diameters ranging from 3 to 24 µm. Analyzed by fluorescence spectroscopy, FTIR spectroscopy, and confocal microscopy, spatially controlled functionalization to generate photopatterned fluorescent polyHIPEs is demonstrated via the reaction with residual acrylate and thiol groups. In addition, the scaffolds can be readily functionalized with external dipolarophiles such as acrylates to incorporate a functionality onto the polyHIPE surface. With many functional tetrazoles also reported in the literature, a PEG-tetrazole is also used to explore the photoinduced functionalization of polyHIPEs possessing tunable ratios of thiol and acrylate groups, and the effect on fluorescence, wettability, and biocompatibility is analyzed. Overall, the reaction is shown to be a broadly applicable tool for polyHIPE functionalization with many avenues for further development toward specific applications.

Continuous-flow self-supported seATRP using a sonicated microreactor.

Continuous-flow simplified electrochemically mediated atom transfer radical polymerization (seATRP) was achieved for the first time without supporting electrolytes (self-supported) using a novel sonicated tubular microreactor. Polymerizations of different acrylic monomers were carried out under different applied currents. The reaction was fast with 75% conversion achieved at ambient temperature in less than 27 minutes. Results also showed good evolution of molecular weight and maintained narrow molecular weight distribution. The reaction rate can be further manipulated by tuning the applied current. Sonication under proper conditions was found to be able to significantly improve both reaction rate and controllability. Self-supported reactions also enable more environmentally friendly and cost-effective operations.

Concurrent control over sequence and dispersity in multiblock copolymers.

Controlling monomer sequence and dispersity in synthetic macromolecules is a major goal in polymer science as both parameters determine materials' properties and functions. However, synthetic approaches that can simultaneously control both sequence and dispersity remain experimentally unattainable. Here we report a simple, one pot and rapid synthesis of sequence-controlled multiblocks with on-demand control over dispersity while maintaining a high livingness, and good agreement between theoretical and experimental molecular weights and quantitative yields. Key to our approach is the regulation in the activity of the chain transfer agent during a controlled radical polymerization that enables the preparation of multiblocks with gradually ascending (Ɖ = 1.16 → 1.60), descending (Ɖ = 1.66 → 1.22), alternating low and high dispersity values (Ɖ = 1.17 → 1.61 → 1.24 → 1.70 → 1.26) or any combination thereof. We further demonstrate the potential of our methodology through the synthesis of highly ordered pentablock, octablock and decablock copolymers, which yield multiblocks with concurrent control over both sequence and dispersity.

Solvent-Independent Molecular Weight Determination of Polymers Based on a Truly Universal Calibration.

Diffusion-ordered NMR spectroscopy (DOSY) allows for accurate molecular weight calibration and determination that can be corrected for solvent influences. Polystyrene and poly(ethylene glycol) standards have been used to calibrate DOSY diffusion data for a variety of solvents, showing a high correlation of data when the bulk viscosity of the solvent is accounted for following the Stokes-Einstein equation. In this way, a type of universal calibration is introduced that allows for determinations of average molecular weight that are at least as accurate as those of traditional size-exclusion chromatography (SEC), if not better. Further, we demonstrate that DOSY calibrations can be used between laboratories, hence removing the need for individual calibration of setups as currently done.

PEGylating poly(p-phenylene vinylene)-based bioimaging nanoprobes.

HYPOTHESIS: Conjugated polymer nanoparticles (CNPs) have attracted considerable attention within bioimaging due to their excellent optical properties and biocompatibility. However, unspecific adsorption of proteins hampers their effective use as advanced bioimaging probes. Controlled methodologies made possible tailor-made functional poly(p-phenylene vinylene), enabling one-pot synthesis of CNPs containing functional surface groups. Hence, it should be feasible to PEGylate these CNPs to tune the uptake by cell lines representative for the brain without imparting their optical properties. EXPERIMENTS: CNPs consisting of the statistical copolymer 2-(5'-methoxycarbonylpentyloxy)-5-methoxy-1,4-phenylenevinylene and poly(2-methoxy-5-(3',7'-dimethoxyoctyloxy)-1,4-phenylenevinylene) were fabricated by miniemulsion solvent evaporation technique. Surface carboxylic acid groups were used to covalently attach amine-terminated polyethylene glycol (PEG) of different molecular weights. We investigated the effect of grafting CNPs with PEG chains on their intrinsic optical properties, protein adsorption behavior and uptake by representative brain cell lines. FINDINGS: PEGylation did not affect the optical properties and biocompatibility of our CNPs. Moreover, a significant decrease in protein corona formation and unspecific uptake in central nervous system cell lines, depending on PEG chain length, was observed. This is the first report indicating that PEGylation does not affect the CNPs role as excellent bioimaging tools and can be adapted to tune biological interactions with brain cells.

Accelerated Polypeptide Synthesis via N-Carboxyanhydride Ring Opening Polymerization in Continuous Flow.

In nature, polypeptide-based materials are ubiquitous, yet their synthetic production is hampered by high cost, limited scalability, and often stringent reaction conditions. Herein an elegant approach is presented for N-carboxyanhydride ring opening polymerization (NCA ROP) of Nε-benzyloxycarbonyl-l-lysine (ZLL) and γ-benzyl-l-glutamate (BLG) NCA in continuous flow. The polymerization is initiated by primary amine initiators using N,N-dimethylformamide (DMF) as solvent. Carrying out the reaction in a silicon microflow reactor speeds up the rate of ROP (92% conversion in 40 min in flow as opposed to 6 h in batch) due to highly efficient permeation of CO2 through the reactor tubing. The polymerization strategy provides a facile, scale-up friendly alternative to traditional batch mode polymerization and has the capability of streamlining NCA ROP.

Kinetic Control of Aggregation Shape in Micellar Self-Assembly.

The first steps towards top-down morphology control in micellar self-assembly are introduced. Kinetically stable micelles are formed from block copolymers (BCPs) using continuous flow techniques by turbulent mixing of water with a THF solution of polymers. In this way, particle shape and size can be altered from spheres to ellipsoids solely via tuning of mixing parameters from a single BCP.

Deconstructing Oligomer Distributions: Discrete Species and Artificial Distributions.

The separation of an oligo(methyl acrylate) distribution, obtained from reversible addition-fragmentation chain transfer (RAFT) polymerization, in a discrete (dispersity=1) oligomeric library (degree of polymerization between 1 and 22) is presented. The properties of this library in terms of diffusivity, glass transition temperature, and viscosity are determined, filling a significant knowledge gap associated with these materials. The obtained oligomer library is used to construct artificial oligomer distributions on demand. These artificial oligomer distributions are used to highlight the potential to tailor physical properties of a material, while concomitantly demonstrating the limitations associated with size-exclusion chromatography analysis of molecular weight and dispersity in particular.

Influence of dielectric layer thickness and roughness on topographic effects in magnetic force microscopy.

Magnetic force microscopy (MFM) has become a widely used tool for the characterization of magnetic properties. However, the magnetic signal can be overlapped by additional forces acting on the tip such as electrostatic forces. In this work the possibility to reduce capacitive coupling effects between tip and substrate is discussed in relation to the thickness of a dielectric layer introduced in the system. Single superparamagnetic iron oxide nanoparticles (SPIONs) are used as a model system, because their magnetic signal is contrariwise to the signal due to capacitive coupling so that it is possible to distinguish between magnetic and electric force contributions. Introducing a dielectric layer between substrate and nanoparticle the capacitive coupling can be tuned and minimized for thick layers. Using the theory of capacitive coupling and the magnetic point dipole-dipole model we could theoretically explain and experimentally prove the phase signal for single superparamagnetic nanoparticles as a function of the layer thickness of the dielectric layer. Tuning the capacitive coupling by variation of the dielectric layer thickness between nanoparticle and substrate allows the distinction between the electric and the magnetic contributions to the MFM signal. The theory also predicts decreasing topographic effects in MFM signals due to surface roughness of dielectric films with increasing film thickness.

Learning from Peptides to Access Functional Precision Polymer Sequences.

Functional precision polymers based on monodisperse oligo(N-substituted acrylamide)s and oligo(2-substituted-α-hydroxy acid)s have been synthesized. The discrete sequences originate from a direct translation of side-chain functionality sequences of a peptide with well-studied properties. The peptide was previously selected to solubilize the photosensitizer meta-tetra(hydroxyphenyl)chlorin. The resulting peptidomimetic formulation additives preserve the drug solubilization and release characteristics of the parent peptide. In some cases, superior properties are obtained, reaching up to 40 % higher payloads and 27-times faster initial drug release.

Automated Polymer Synthesis Platform for Integrated Conversion Targeting Based on Inline Benchtop NMR.

An automated polymer synthesis platform based on an inline low-field nuclear magnetic resonance spectrometer is developed. Flow chemistry and automated inline analyses are an excellent combination for automated kinetic screening and for self-optimizing reactions with programmable conversion targeting. By monitoring monomer conversion over a continuous range of reactor residence times, the platform is able to construct kinetic profiles of polymerizations in an accurate and efficient way. The machine-assisted self-optimization routine allows the reaction to be stopped at any given preselected conversion, giving rise to unprecedented reproducibility in polymer synthesis.

Precise Polymer Synthesis by Autonomous Self-Optimizing Flow Reactors.

A novel continuous flow system for automated high-throughput screening, autonomous optimization, and enhanced process control of polymerizations was developed. The computer-controlled platform comprises a flow reactor coupled to size exclusion chromatography (SEC). Molecular weight distributions are measured online and used by a machine-learning algorithm to self-optimize reactions towards a programmed molecular weight by dynamically varying reaction parameters (i.e. residence time, monomer concentration, and control agent/initiator concentration). The autonomous platform allows targeting of molecular weights in a reproducible manner with unprecedented accuracy (<2.5 % deviation from pre-selected goal) for both thermal and light-induced reactions. For the first time, polymers with predefined molecular weights can be custom made under optimal reaction conditions in an automated, high-throughput flow synthesis approach with outstanding reproducibility.

Synthesis of Functional Polymer Particles from Morita-Baylis-Hillman Polymerization.

Functional synthetic polymers are frequently explored for their use in the biomedical field. To fulfill the stringent demands of biodegradability and compatibility, the materials need to be versatile and tunable. Post-modification is often considered challenging for well-known degradable materials like poly(lactic acid) because of their chemical inertness. In this work a procedure is proposed to produce densely functionalized polymer particles using oligomeric precursors synthesized via the Morita-Baylis-Hillman reaction. This allows for a variety of post-modification reactions to serve bio-conjugation or tuning of the material properties. The particles are subjected to basic media and found to be degradable. Furthermore, cytotoxicity tests confirm good biocompatibility. Finally, as a proof of concept to demonstrate the versatility of the particles, post-modification reactions are carried out through the formation of imines.

Ultrafast PhotoRAFT Block Copolymerization of Isoprene and Styrene Facilitated through Continuous-Flow Operation.

Polymers made from isoprene and styrene resemble an important class of synthetic macromolecules found in a wide range of everyday commodity products. Their synthesis is usually limited to radical emulsion or anionic polymerization. Herein, we report on ultrafast photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization of isoprene and styrene in a continuous-flow microreactor. The cooperative action of a high photoinitiation efficiency and use of elevated temperatures considerably reduces the reaction times to less than half an hour to give high monomer conversions, allowing for the first time polyisoprene to be yielded from controlled radical polymerization in high definition and reasonable reaction times. High chain-end fidelities are maintained and block copolymers were prepared including a polystyrene-block-polyisoprene-block-polystyrene (PS-b-PI-b-PS) triblock copolymer.

Micro-patterned molecularly imprinted polymer structures on functionalized diamond-coated substrates for testosterone detection.

Molecularly imprinted polymers (MIPs) can selectively bind target molecules and can therefore be advantageously used as a low-cost and robust alternative to replace fragile and expensive natural receptors. Yet, one major challenge in using MIPs for sensor development is the lack of simple and cost-effective techniques that allow firm fixation as well as controllable and consistent receptor material distribution on the sensor substrate. In this work, a convenient method is presented wherein microfluidic systems in conjunction with in situ photo-polymerization on functionalized diamond substrates are used. This novel strategy is simple, efficient, low-cost and less time consuming. Moreover, the approach ensures a tunable and consistent MIP material amount and distribution between different sensor substrates and thus a controllable active sensing surface. The obtained patterned MIP structures are successfully tested as a selective sensor platform to detect physiological concentrations of the hormone disruptor testosterone in buffer, urine and saliva using electrochemical impedance spectroscopy. The highest added testosterone concentration (500 nM) in buffer resulted in an impedance signal of 10.03 ±â€¯0.19% and the lowest concentration (0.5 nM) led to a measurable signal of 1.8 ±â€¯0.15% for the MIPs. With a detection limit of 0.5 nM, the MIP signals exhibited good linearity between a 0.5 nM and 20 nM concentration range. Apart from the excellent and selective recognition offered by these MIP structures, they are also stable during and after the dynamic sensor measurements. Additionally, the MIPs can be easily regenerated by a simple washing procedure and are successfully tested for their reusability.