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)

All-aqueous continuous-flow RAFT dispersion polymerisation for efficient preparation of diblock copolymer spheres, worms and vesicles

We report the scalable, all-aqueous synthesis of polyIJdimethylacrylamide)–polyIJdiacetone acrylamide) (PDMAm–PDAAm) diblock copolymer spheres, worms and vesicles by reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerisation in a low-cost continuous-flow (CF) reactor. A transient state kinetic profiling method using a 5 mL reactor coil indicated a considerably faster rate than the equivalent batch reaction. Higher throughput was subsequently demonstrated by employing a 20 mL coil reactor for the synthesis of a 135 g, 30% w/w batch of PDMAm113 macromolecular chain transfer agent (macro-CTA) at 98% conversion. This was used without further purification to polymerise DAAm in a CF reactor. During this polymerisation, the chains underwent polymerisation-induced self-assembly (PISA) producing block copolymer spheres. This reaction also proceeded faster than in batch, and the high resolution kinetics enabled clear observation of the rate enhancement which is characteristic of PISA systems. GPC studies indicated the formation of a copolymer with low molar mass dispersity and complete blocking efficiency, despite the high conversion achieved during the precursor macro-CTA synthesis. It was subsequently demonstrated that the PDMAm113 macro-CTA could be used to prepare PDMAm113–PDAAmx block copolymer spheres (where x = 50, 100 and 200) with systematically increasing particle diameters. Finally, by reducing the PDMAm macro-CTA DP to 50 and increasing total solids to 20% w/w, it was possible to prepare worms and vesicles in the tubular reactor by tailoring the residence time to achieve specific degrees of polymerisation of the PDAAm block

Poly(methyl methacrylate)-silica microcapsules synthesized by templating Pickering emulsion droplets

In this contribution, we present the silica microencapsulation of hydrophilic compounds by templating Pickering emulsion droplets without contamination of the dispersed phase with either a catalyst or the silica precursor. This is accomplished by the use of an amphiphilic catalyst, which situates around the Pickering emulsion droplets and directs the reaction to the interface. Both silica precursor and the amphiphilic catalyst are soluble in the oil phase and therefore initially do not reside in the hydrophilic microcapsule templates. The thickness of the capsules can be tuned by adjusting the amount of precursor. Thus, the permeability of the capsules can in principle be controlled. The possibility of tuning the permeability holds promise for a variety of applications of the microcapsules. Because of the straightforward synthesis method and by minimizing mixing of the core with contaminants, the technique is potentially suitable for the encapsulation of delicate matter including live organisms, drugs, enzymes or bacteria

Poly(methyl methacrylate)-silica microcapsules by templating Pickering emulsion droplets

Please help populate SUNScholar with the full text of SU research output. Also - should you need this item urgently, please send us the details and we will try to get hold of the full text as quick possible. E-mail to [email protected]. Thank you.Journal Articles (subsidised)NatuurwetenskappeChemie & Polimeerwetenska

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)

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