Facile synthesis of well-defined MDMO-PPV containing (tri)block-copolymers via controlled radical polymerization and CuAAC conjugation

A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene) (PPV) materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA) concentration and reaction temperature. For the chain transfer constant, a negative activation energy of −12.8 kJ·mol−1 was deduced. Good control over molecular weight is achieved for both the sulfinyl and the dithiocarbamate route (DTC). PPVs with molecular weights ranging from thousands to ten thousands g·mol−1 were obtained. To allow for a meaningful analysis of the CTA influence, Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were determined for conjugated MDMO-PPV ([2-methoxy-5-(3',7'-dimethyloctyloxy)]-1,4-phenylenevinylene) to α = 0.809 and k = 0.00002 mL·g−1. Further, high-endgroup fidelity of the CBr4-derived PPVs was proven via chain extension experiments. MDMO-PPV-Br was successfully used as macroinitiator in atom transfer radical polymerization (ATRP) with acrylates and styrene. A more polar PPV counterpart was chain extended by an acrylate in single-electron transfer living radical polymerization (SET-LRP). In a last step, copper-catalyzed azide alkyne cycloaddition (CuAAC) was used to synthesize block copolymer structures. Direct azidation followed by macromolecular conjugation showed only partial success, while the successive chain extension via ATRP followed by CuAAC afforded triblock copolymers of the poly(p-phenylene vinylene)-block-poly(tert-butyl acrylate)-block-poly(ethylene glycol) (PPV-b-PtBuA-b-PEG)

Particle Size Control in Miniemulsion Polymerization via Membrane Emulsification

y Miniemulsion polymerization of methyl methacrylate has been conducted employing Shirasu porous glass (SPG) membrane emulsification for the generation of the initial miniemulsion. For the first time, submicron-sized monomer droplets and polymer particles have been prepared using membranes with pore sizes significantly smaller than those previously reported. Membrane pore sizes of diameters 100-400 nm were explored, demonstrating that the final particle size can be conveniently tuned within the diameter range of 250-1600 nm. The choice of radical initiator is crucial: a sufficiently hydrophobic initiator (lauroyl peroxide) is required to minimize the generation of bimodal particle size distributions via secondary nucleation. Given the advantages of low energy consumption, reduced shear stress (compared with conventional high-energy mixing approaches such as ultrasonication), and an easily adjustable particle size via the membrane pore size, membrane emulsification has significant potential for the synthesis of polymeric nanoparticles via miniemulsion polymerization.The authors acknowledge the European Union Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 665501 with the research Foundation Flanders (FWO) (N.Z.)

Visible Light-Mediated Polymerization-Induced Self-Assembly Using Continuous Flow Reactors

We present the synthesis of polymeric nano-particles of targeted morphology in a continuous process via visible light-mediated aqueous RAFT polymerization-induced self-assembly (PISA). A trithiocarbonate-derived poly-(ethylene glycol) (PEG) macroRAFT was activated in the presence of hydroxypropyl methacrylate (HPMA) at 37 degrees C under blue light irradiation (460 nm), leading to the formation of PEG-b-P(HPMA) nanoparticles. The method is attractive in its simplicity-spheres, worms, and vesicles can easily be obtained in a continuous fashion with higher control in comparison to conventional batch procedures. This allows for more accurate production of particle morphologies and scalable synthesis of these nano-objects. The versatility of this process was demonstrated by the in situ encapsulation of an active compound.MCSC-IF-GF [12U1717N

Differences in Wear and Material Integrity of NAO and Low-Steel Brake Pads under Severe Conditions

In this study, through severe reduced-scale braking tests, we investigate the wear and integrity of organic matrix brake pads against gray cast iron (GCI) discs. Two prototype pad materials are designed with the aim of representing a typical non-metal NAO and a low-steel (LS) formulation. The worn surfaces are observed with SEM. The toughness of the pad materials is tested at the raw state and after a heat treatment. During braking, the LS-GCI disc configuration produces heavy wear. The friction parts both keep their macroscopic integrity and wear appears to be homogeneous. The LS pad is mostly covered by a layer of solid oxidized steel. The NAO-GCI disc configuration wears dramatically and cannot reach the end of the test program. The NAO pad suffers many deep cracks. Compacted third body plateaus are scarce and the corresponding disc surface appears to be very heterogeneous. The pad materials both show similar strength at the raw state and similar weakening after heat treatment. However, the NAO material is much more brittle than the LS material in both states, which seems to favor the growth of cracks. The observations of crack faces suggest that long steel fibers in the LS material palliate the brittleness of the matrix, even after heat damage

Facile Synthesis of Well-Defined MDMO-PPV Containing (Tri)Block—Copolymers via Controlled Radical Polymerization and CuAAC Conjugation

A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene) (PPV) materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA) concentration and reaction temperature. For the chain transfer constant, a negative activation energy of −12.8 kJ·mol−1 was deduced. Good control over molecular weight is achieved for both the sulfinyl and the dithiocarbamate route (DTC). PPVs with molecular weights ranging from thousands to ten thousands g·mol−1 were obtained. To allow for a meaningful analysis of the CTA influence, Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were determined for conjugated MDMO-PPV ([2-methoxy-5-(3\u27,7\u27-dimethyloctyloxy)]-1,4-phenylenevinylene) to α = 0.809 and k = 0.00002 mL·g−1. Further, high-endgroup fidelity of the CBr4-derived PPVs was proven via chain extension experiments. MDMO-PPV-Br was successfully used as macroinitiator in atom transfer radical polymerization (ATRP) with acrylates and styrene. A more polar PPV counterpart was chain extended by an acrylate in single-electron transfer living radical polymerization (SET-LRP). In a last step, copper-catalyzed azide alkyne cycloaddition (CuAAC) was used to synthesize block copolymer structures. Direct azidation followed by macromolecular conjugation showed only partial success, while the successive chain extension via ATRP followed by CuAAC afforded triblock copolymers of the poly(p-phenylene vinylene)-block-poly(tert-butyl acrylate)-block-poly(ethylene glycol) (PPV-b-PtBuA-b-PEG)

A Simple and Versatile Pathway for the Synthesis of Visible Light Photoreactive Nanoparticles

This work pioneers the design of visible (415 nm) and UV-B light (300 nm) reactive nanoparticles via radical polymerization in aqueous heterogeneous media based on methyl methacrylate (MMA) and unique acrylates bearing tetrazole functionalities in a simple and straightforward two step reaction. Stable colloidal nanoparticles with an average diameter of 150 nm and inherent tetrazole functionality (varying from 2.5 to 10 wt% relative to MMA) are prepared via one-pot miniemulsion polymerization. In a subsequent step, fluorescent pyrazoline moieties serving as linkage points are generated on the nanoparticles by either photoinduced nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) or nitrile imine carboxylic acid ligation (NICAL) in water, thus enabling the particles as fluorescent tracers. Through in-depth molecular surface analysis, it is demonstrated that the photoreactive nanoparticles undergo ligation to a variety of substrates bearing functionalities including maleimides, acrylates, or carboxylic acids, illustrating the versatility of the particle modification process. Critically, the unique ability of the photoreactive nanoparticles to be activated with visible light allows for their decoration with UV light-sensitive molecules. Herein, the ligation of folic acida vitamin prone to degradation under UV light-to the photoreactive nanoparticles using visible light is exemplified, demonstrating the synthetic power of our photoreactive fluorescent nanoparticle platform technology.L.D. and N.Z. contributed equally to this work. C.B.-K. acknowledges the Australian Research Council (ARC) for funding in the form of a Laureate Fellowship underpinning his photochemical research program as well as the Queensland University of Technology (QUT) for key continued support. N.Z. is grateful for the funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 665501 with the research Foundation Flanders (FWO). The XPS data of the latexes after the NICAL or NITEC reactions reported herein were obtained at the Central Analytical Research Facility (CARF) operated by the Institute for Future Environments (IFE). Access to CARF is supported by generous funding from the Science and Engineering Faculty (SEF).biomolecule tagging; miniemulsion; profluorescent particles; tetrazole-driven photochemistry; visible light ligatio

Visible Light-Mediated Polymerization-Induced Self-Assembly Using Continuous Flow Reactors

We present the synthesis of polymeric nanoparticles of targeted morphology in a continuous process via visible light-mediated aqueous RAFT polymerization-induced self-assembly (PISA). A trithiocarbonate-derived poly­(ethylene glycol) (PEG) macroRAFT was activated in the presence of hydroxypropyl methacrylate (HPMA) at 37 °C under blue light irradiation (460 nm), leading to the formation of PEG-<i>b</i>-P­(HPMA) nanoparticles. The method is attractive in its simplicityspheres, worms, and vesicles can easily be obtained in a continuous fashion with higher control in comparison to conventional batch procedures. This allows for more accurate production of particle morphologies and scalable synthesis of these nano-objects. The versatility of this process was demonstrated by the <i>in situ</i> encapsulation of an active compound

Exploring the photochemical reactivity of multifunctional photocaged dienes in continuous flow

Flow reactors become more and more automated by enabling on-line reaction monitoring and adjusting the process parameters. On-line monitoring of chemical processes is a valuable tool to steer processes, leading to precise engineering of macromolecular materials. Detailed information about specific product patterns, end-group functionality or material composition can be obtained by coupling a flow reactor to a mass spectrometer (e. g. ESI-MS). In this work, we study the deprotection of maleimides and its subsequent photoenol functionalization to synthesize complex macromolecules using a photo flow reactor coupled to an ESI-MS. Using a trapping agent (TA), furan is efficiently removed from the maleimide Diels−Alder adduct within just minutes at 175 °C and quantitatively converted into an unreactive species that does not interfere with further reactions of the maleimide. The photoenol reaction was likewise shown to be highly effective to proceed in microreactors, reaching quantitative conversion of trifunctional molecules in as little as 2 min.</p

Improved mechanistic insights into radical sulfinyl precursor MDMO-PPV synthesis by combining microflow technology and computer simulations

A kinetic model using Predici is developed and applied to obtain an improved mechanistic understanding of the radical sulfinyl precursor polymerization route for poly(2-methoxy-5-(3'-7'-dimethyloctyloxy-4-((octylsulfinyl)methyl))-1,4-phenylenevinylene) (MDMO-PPV) synthesis. In this route, the premonomer-1-(chloromethyl)-5-((3,7-dimethyloctyl)-oxy)-2-methoxy-4-((octylsulfinyl)methyl)benzene (MDMO) is subjected to a base-induced elimination reaction using NatBuO as base and s-BuOH as solvent. Microreactors are used to ensure rapid mixing of reaction components and sharp quenching at precisely determined time points. Systematic kinetic data that follows the very fast precursor polymerizations with reaction time have in this way become available for the first time. Via the applied kinetic model, the presence of a chain transfer reaction is unambiguously confirmed and kinetic rate coefficients have been deduced, which fall within the typical expectations of radical chain reactions. Two models were further compared, one including chain reinitiation (noninhibition model) and one excluding reinitiation (inhibition model) of the by chain transfer-generated radical species. Investigation of trend lines suggest a preference of the reinitiation model, thereby implying that MDMO-PPV synthesis follows mostly a conventional free radical polymerization mechanism that only differs with respect to its initiation mode and the biradical nature of the propagation step

Rapid Oxygen Tolerant Aqueous RAFT Photopolymerization in Continuous Flow Reactors

Recently, new controlled polymerization pathways have emerged for the synthesis of functional polymer materials. The use of light, particularly visible light, to generate radicals has shown to be beneficial over thermal induction due to the high control over reaction parameters as well as spatiotemporal control. Although numerous photopolymerizations have been performed in batch, additional initiators or activators are often needed to increase the overall yield, making this process time-consuming and costly; optical path lengths directly correlate with achievable space-time yields. The use of flow reactors is in this case advantageous. In this work, new synthetic protocols are demonstrated for the synthesis of di- and triblock copolymers in tubular reactors via photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. Within just 10 min of polymerization time, full monomer conversion was reached for a variety of acrylamides and acrylates, and polymers with molecular weights up to 100000 g mol(-1) and high end-group fidelity were obtained. Changing the flow rates, concentrations, and light intensity allowed alteration of the molecular weights, and several di- and triblock copolymers were synthesized, indicating the high level of control over the polymerization. In addition, multiple flow reactors were coupled to allow the synthesis of triblock copolymers in a reactor cascade process without the need for intermediate purification. The attractiveness of this approach is illustrated by considering that a PDMAA-b-PDMAA-b-PDMAA triblock copolymer with a number-average molecular weight of 3200 g mol(-1) and dispersity of 1.24 could be theoretically obtained at a rate of 300 g/day.MCSC-IF-GF applicant no. 12U1717N. We acknowledge The European Union Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 665501 with the research Foundation Flanders (FWO) (N.Z.)