Photo-induced copper-mediated polymerization of methyl acrylate in continuous flow reactors

Photo-induced copper-mediated radical polymerization of methyl acrylate (MA) is carried out in DMSO at 15 °C in a tubular photo-flow reactor as well as in a glass-chip based microreactor. Polymerization reactions proceed rapidly to approximately 90% monomer conversion within 20 minutes of reactor residence time. Control of reactions is high as evidenced by ideal polymerization kinetics, low dispersities of the obtained polymers (in the range of 1.1) and linear evolution of number average molecular weights during polymerization reactions. Poly(MA) with average molecular weights between a few hundred and ∼5000 g mol−1 was obtained under retention of pristine end group fidelity. Besides homopolymers, block copolymers can also be successfully synthesized and poly(methyl acrylate)-b-poly(butyl acrylate) block copolymers with a similar low dispersity are obtained. Reactions proceed under homogeneous reaction conditions. This feature allows the reaction to be carried out in milli- and also in microflow devices. In both cases, equally good control is achieved with only minimal adaptation of the reaction protocol, underpinning the simplicity and fast adaptability of the protocol to different flow reactors

Search for quark contact interactions and extra spatial dimensions using dijet angular distributions in proton-proton collisions at √s = 8 TeV

A search is presented for quark contact interactions and extra spatial dimensions in proton-proton collisions at s = 8 TeV using dijet angular distributions. The search is based on a data set corresponding to an integrated luminosity of 19.7 -1 collected by the CMS detector at the CERN LHC. Dijet angular distributions are found to be in agreement with the perturbative QCD predictions that include electroweak corrections. Limits on the contact interaction scale from a variety of models at next-to-leading order in QCD corrections are obtained. A benchmark model in which only left-handed quarks participate is excluded up to a scale of 9.0 (11.7) TeV for destructive (constructive) interference at 95% confidence level. Lower limits between 5.9 and 8.4 TeV on the scale of virtual graviton exchange are extracted for the Arkani-Hamed-Dimopoulos-Dvali model of extra spatial dimensions

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)

MaDDOSY (Mass Determination Diffusion Ordered Spectroscopy) using an 80 MHz bench top NMR for the rapid determination of polymer and macromolecular molecular weight

YesMeasurement of molecular weight is an integral part of macromolecular and polymer characterization which usually has limitations. Herein, we present the use of a bench-top 80 MHz 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.Royal Society. Grant Number: URF∖R1∖180274. Engineering and Physical Sciences Research Council. Grant Numbers: EP/V037943/1, EP/V007688/1, EP/V036211/

The role of mid-chain radicals in acrylate free radical polymerization: Branching and scission

The past 5 years have seen a significant increase in the understanding of the fate of so-called mid-chain radicals (MCR), which are formed during the free radical polymerization of monomers that form highly reactive propagating radicals and contain an easily abstractable hydrogen atom. Among these monomers, acrylates are, beside ethylene, among the most promi-nent. Typically, a secondary propagating acrylate-type macro-radical (SPR) can easily transfer its radical functionality via a six-membered transition state to a position within the polymer chain (in a so-called backbiting reaction), creating a tertiary MCR. Alternatively, the radical function can be transferred intramolecularly to any position within the chain (also forming an MCR) or intermolecularly to another polymer strand. This article aims at providing a comprehensive overview of the up-to-date knowledge about the rates at which MCRs are formed, their secondary reactions as well as the consequences of their occurrence under variable reaction conditions. We explore the latest aspects of their detection (via electron spin resonance spectroscopy) as well as the characterization of the polymer structures to which they lead (via high resolution mass spectrometry). The presence of MCRs leads to the formation of branched polymers and the partial formation of polymer networks. They also limit the measurement of kinetic parameters (such as the SPR propagation rate coefficient) with conventional methods. However, their occurrence can also be used as a synthetic handle, for example, the high-temperature preparation of macromonomers. © 2008 Wiley Periodicals, Inc

Investigation of the End Group Fidelity at High Conversion during Nitroxide-Mediated Acrylate Polymerizations

International audienceThe impact of formation of midchain radicals?and more specifically the follow up reactions of ?-scission and macromonomer addition to propagating macroradicals stemming from this process?on the nitroxide-mediated polymerization of acrylates have been studied via kinetic modeling with the software package Predici on the example of butyl acrylate polymerization at 120 °C. Only small influences of the midchain radical formation on the livingness of the process is observed, however, large effects must be envisaged by the (reverse) scission reaction at high monomer-to-polymer conversions. A significant loss of livingness, depending on the temperature, monomer and initiator concentration must be expected at elevated stages of polymerizations. For a polymerization at 120 °C and a target chain length of 100, less than 75% livingness of the polymer product can be expected at 80% conversion. From this point of polymerization on, significant broadening of the overall polymer product is predicted in accordance to literature data and eventually the chain-length?conversion relation is lost at the end of reaction

Continuous Microflow PhotoRAFT Polymerization

PhotoRAFT (reversible addition–fragmentation radical transfer) polymerizations are investigated for reactions induced by conventional radical photoinitiators. As demonstrated, this rather simple photoRAFT reaction shows similar outcomes compared to other recently introduced photopolymerizations, such as photoelectron transfer RAFT or copper-mediated photopolymerization. Despite the general notion that classically initiated photoRAFT yields unsatisfactory results, it is shown that good results can be achieved when conditions are selected accordingly. Not only the type of initiator is of importance, also light intensity, RAFT agent to initiator concentration, and reaction temperature are of importance. For the initiator benzoin, optimal polymerizations are obtained when the initiator is used in a ratio of 0.25 to the initial RAFT agent at 60 °C reaction temperature and 30 mW cm^–2 light intensity (365 nm). Chain lengths of the polymer can be tuned efficiently and block copolymers are accessible from the process despite some slight loss in chain-end fidelity during polymerizations. Additionally, the choice of initiator is shown to have a large effect on the polymerization, which can be routed to different decomposition rate coefficient under the same illumination conditions. Decomposition rates of the photoinitiators are under flow conditions very high, and polymerizations proceed to completion after all initiator is used up via a photoiniferter mechanism