Polymer Synthesis in Continuous Flow Reactors

A variety of polymerizations has long been performed in continuous flow reactors on an industrial scale; comparatively, on smaller scales, continuous polymerization methods have only gained significant attention in recent years. Yet, within the last decade, the field has moved from the rare occurrence of flow reactors to their abundant use today. A wide variety of polymer reactions have been performed in a continuous fashion on small and intermediate scales. The advantages of applying flow chemistry principles for polymer reactions include increased reproducibility and synthetic precision, significant increases in reaction performances for photochemical reactions, the ability to couple reactors to create complex materials in a single reactor pass, as well as the unique combination of online monitoring and machine learning. In this review we give a comprehensive overview of polymer reactions being carried out in continuous flow reactors to date. The development of the field is discussed, concluding with the most recent examples on automated polymer synthesis, reactor telescoping and nanoparticle synthesis. Finally, the design of flow reactors is discussed to help newcomers contribute to the current and future developments in the field

Enhanced osteogenic differentiation of human fetal cartilage rudiment cells on graphene oxide-PLGA hybrid microparticles

Poly(d,l–lactide–co–glycolide) (PLGA) has been extensively explored for bone regeneration applications; however, its clinical use is limited by low osteointegration. Therefore, approaches that incorporate osteoconductive molecules are of great interest. Graphene oxide (GO) is gaining popularity for biomedical applications due to its ability to bind biological molecules and present them for enhanced bioactivity. This study reports the preparation of PLGA microparticles via Pickering emulsification using GO as the sole surfactant, which resulted in hybrid microparticles in the size range of 1.1 to 2.4 µm based on the ratio of GO to PLGA in the reaction. Furthermore, this study demonstrated that the hybrid GO-PLGA microparticles were not cytotoxic to either primary human fetal cartilage rudiment cells or the human osteoblast-like cell line, Saos-2. Additionally, the GO-PLGA microparticles promoted the osteogenic differentiation of the human fetal cartilage rudiment cells in the absence of exogenous growth factors to a greater extent than PLGA alone. These findings demonstrate that GO-PLGA microparticles are cytocompatible, osteoinductive and have potential as substrates for bone tissue engineering

Strategies for reduction of graphene oxide – A comprehensive review

Graphene continues to draw considerable research and commercial interest due to its applicability in a variety of industries. There have been various approaches developed to produce high quality graphene in commercial quantities in order to be able to meet the ever-increasing demand from industry. Despite over a decade of research and various examples of lab-scale success in producing highly pure single graphene sheets, there remain considerable challenges in translating them into a commercial success in terms of their large-scale production. To this end, reduction of graphene oxide (GO) is considered the most viable alternative approach to produce highly quality graphene. However, there have been numerous reports documenting a variety of reductants in the literature, making it quite difficult to assess and compare these strategies from the perspective of large-scale commercial production. In this review, we present a critical survey of various reduction methods adopted towards the reduction of GO enabled by chemical, plant extracts, microorganisms and photoreduction with special emphasis on their reduction mechanism and electrical conductivity of the resulting rGO. We also provide a prospective to draw attention to the considerable challenges persisting towards the structural and electronic properties of the synthesised rGO which is limiting the true commercial translation of these materials

RAFT Emulsion Polymerization: MacroRAFT Agent Self-Assembly Investigated Using a Solvachromatic Dye

Polymerization-induced self-assembly (PISA) and amphiphilic-macroRAFT-mediated emulsion polymerization are commonly used approaches for synthesis of well-defined polymers and sophisticated particle morphologies. One aspect of these systems that remains relatively unexplored is the conformational state of macroRAFT agents in aqueous solution. To redress this deficiency, we have used fluorescence spectrometry experiments to conduct detailed investigations of the coil conformation across a wide range of pH values for a series of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) macroRAFT agents with different Z-groups (-S-(CH2)2-COOH, -S-(CH2)3-CH3, and -S-(CH2)11-CH3), as well as amphiphilic macroRAFT agents (PMAA-b-poly(methyl methacrylate)(PMMA) and PAA-b-polystyrene(PS)). The critical aggregate concentrations (CAC) or critical micelle concentrations (CMC) for all systems ranged from 7.48 × 10-7to 2.57 × 10-3mol L-1. Overall, an extensive library of CAC/CMC values has been compiled for PAA- and PMAA-based macroRAFT agents at different pH conditions, providing important information related to the mechanistic understanding and optimization of macroRAFT-assisted emulsion polymerization

Reversible AdditionFragmentation Chain Transfer (RAFT) polymerization in miniemulsion based on in situ surfactant generation

Reversible additionfragmentation chain transfer (RAFT) polymerization of styrene has been implemented in aqueous miniemulsion based on the in situ surfactant generation approach using oleic acid and potassium hydroxide in the absence of high energy mixing. The best results were obtained using the RAFT agent 3-benzylsulfanyl thiocarbonyl sufanylpropionic acid (BSPAC), most likely as a result of the presence of a carboxylic acid functionality in the RAFT agent that renders it surface active and thus imparts increased colloidal stability. Stable final miniemulsions were obtained with no coagulum with particle diameters less than 200nm. The results demonstrate that the RAFT miniemulsion polymerization of styrene employing the low energy in situ surfactant method is challenging, but that a system that proceeds predominantly by a miniemulsion mechanism can be achieved under carefully selected conditions. © 2011 CSIRO

Retardation in RAFT polymerization: Does cross-termination occur with short radicals only?

The recently proposed model by Perrier and co-workers [J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 3455 ] to account for retardation effects in dithiobenzoate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene has been tested experimentally. According to this model, retardation is caused by cross-termination of very short radicals only. Polymerizations were conducted employing a macroazoinitiator and a polymeric RAFT agent based on cumyl dithiobenzoate, thereby effectively eliminating all short radicals from the system. The results show, in basic agreement with the model, that there is very little, if any, retardation in dithiobenzoate-mediated RAFT polymerization of styrene in the absence of short radicals. © 2011 American Chemical Society

Miniemulsion polymerization based on in situ surfactant formation without high-energy homogenization: Effects of organic acid and counter ion

Miniemulsion polymerization of styrene based on the in situ surfactant-generation technique has been investigated for a range of carboxylic acids and counterions. This technique relies on in situ formation of the surfactant at the oil-water interface and circumvents the use of traditional high-energy mixing (for example, ultrasonication) for generation of the initial miniemulsion. Miniemulsion polymerizations have been conducted successfully using the carboxylic acids lauric acid, palmitic acid and oleic acid, respectively. Coagulation/phase separation was not observed and the number-average particle diameters were < 100 nm. The counterions K +, Na + and Li + were investigated in combination with five different carboxylic acids (all permutations), revealing that satisfactory miniemulsion formation/stability could only be obtained with K +. Results of miniemulsion polymerizations conducted in the presence of an aqueous-phase radical scavenger were consistent with predominant monomer droplet nucleation. Use of the corresponding preformed surfactants added to the aqueous phase, without high-energy mixing, did not result in sufficiently stable initial (before polymerization) miniemulsions. © 2012 The Society of Polymer Science, Japan (SPSJ) All rights reserved