Absolute electron spray ionization mass spectrometry (ESI-MS) data are reported, for the first time, over the complete chain length range for the synthesis of welldefined macromonomers (MMs) obtained via activation of bromine-capped poly(n-butyl acrylate) (0.1 mass %; solvent: anisole; 140 degrees C) with CuBr2/Me6TREN (Me6TREN: tris(2-(dimethylamino)ethyl)amine) and tin ethylhexanoate. These data are generated based on bivariate kinetic Monte Carlo simulations, tracking the chain lengths and the positions of radicals/characteristic groups along the chains (>100 reactions, 12 radical/dormant species types, and 7 characteristic end/ mid-groups). Based on qualitative tuning to experimental data, migration is found to be 50 times slower than backbiting but 15 times faster than beta C-scission, making it a dominant reaction. Benefiting from the absence of monomer, the chain transfer to polymer rate coefficient is assessed as 6 x 10(2) L mol(-1) s(-1) (140 degrees C). Model analysis shows that consecutive backbiting/migration/beta C-scission leads to a favoring of MMs with even chain lengths and a hydrogen chain end over MMs with the nonreactive chain end originating from the initial dormant polymer. The obtained insights contribute to a better fundamental understanding of hydrogen abstractions in acrylate radical polymerization and open the path for a more detailed polymer product characterization in general.

Continuous flow synthesis techniques have in recent years conquered laboratory scale synthesis, yet within the field of precision polymer synthesis its use is still not fully established despite the large advantages that can be gained from switching from classical batch-wise chemistry to flow chemistry, often already by using relatively simple chip-based or cheap tubular micro- and mesoscaled reactors. Translating a polymerization from batch to continuous flow marks not only a mere change in reactor engineering, but also leads to numerous advantages in the polymerization with respect to kinetics of processes and especially product quality. In flow, polymerizations are not only speed up, they also provide materials with better dispersities and higher chain end fidelities when conditions are chosen accordingly. The underpinning effects causing these improvements are demonstrated and discussed. Further, also information on required laboratory equipment and recent developments in online reaction monitoring are highlighted to give newcomers to the field an idea about the potential of continuous flow polymerization.

Photochemical Processes in Continuous-Flow Reactors, pp. 213-244 (2017) No AccessChapter 8: Photoflow Material SynthesisBenjamin Wenn and Thomas JunkersBenjamin WennPolymer Reaction Design Group Institute for Materials Research (IMO), Universiteit Hasselt Martelarenlaan 42, 3500 Hasselt, Belgium and Thomas JunkersPolymer Reaction Design Group Institute for Materials Research (IMO), Universiteit Hasselt Martelarenlaan 42, 3500 Hasselt, BelgiumIMEC Associated Lab IMOMEC, Wetenschapspark 1, 3590 Diepenbeek, Belgiumhttps://doi.org/10.1142/9781786342195_0008Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: The following sections are included: Introduction Continuous Photoinitiated Controlled Radical Polymerization Polymer Modification in Photoflow Reactors Microparticles from UV-Photoflow Polymerization Inorganic Materials from Flow Process Conclusion References FiguresReferencesRelatedDetails Photochemical Processes in Continuous-Flow ReactorsMetrics History PDF download

Propagation rate coefficient values, k p , reported by several groups for radical polymerization of bulk vinyl acetate are critically evaluated. All data are obtained by the combination of pulsed‐laser polymerization and subsequent polymer analysis by size exclusion chromatography, as recommended by the IUPAC Working Party on Modeling of Polymerization Kinetics and Processes. Although a small (≈15%) increase in k p is observed as laser pulse repetition rate is increased from low (25–100 Hz) to high (300–500 Hz) values, all of the data fulfill the required consistency criteria and thus are combined into a benchmark set covering the temperature range of 5–70 °C. The data are fitted well by an Arrhenius relation resulting in a pre‐exponential factor of 1.35 × 10 7 L mol −1 s −1 and an activation energy of 20.4 kJ mol −1 , with 95% confidence ellipsoids for the parameters also presented. image

Photomediated controlled radical polymerization is a versatile method to prepare, under mild conditions, various well-defined polymers with complex architecture, such as block and graft copolymers, sequence-controlled polymers, or hybrid materials via surface-initiated polymerization. It also provides opportunity to manipulate the reaction through spatiotemporal control. This review presents a comprehensive account of the fundamentals and applications of various photomediated CRP techniques, including atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), nitroxide mediated polymerization (NMP) and other procedures. In addition, mechanistic aspects of other photomediated methods are discussed.

Detailed knowledge of the polymerization mechanisms and kinetics of academically and industrially relevant monomers is mandatory for the precision synthesis of tailor-made polymers. The IUPAC-recommended pulsed-laser polymerization-size exclusion chromatography (PLP-SEC) approach is the method of choice for the determination of propagation rate coefficients and the associated Arrhenius parameters for free radical polymerization processes. With regard to specific monomer classes-such as acrylate-type monomers, which are very important from a materials point of view-high laser frequencies of up to 500 Hz are mandatory to prevent the formation of mid-chain radicals and the occurrence of chain-breaking events by chain transfer, if industrially relevant temperatures are to be reached and wide temperature ranges are to be explored (up to 70 °C). Herein the progress and state-of-the-art of high-frequency PLP-SEC with pulse repetition rates of 500 Hz is reported, with a critical collection of to-date investigated 500 Hz data as well as future perspectives for the field.

Abstract: The synthesis and characterization of a series of dibenzhydryl-based -diimineNi(II) complexes bearing a range of electron-donating or -withdrawing groups are described.Polymerization with ethylene is investigated in detail, involving the activator effect, influenceof polymerization conditions on catalyst activity, thermal stability, polymer molecular weight andmelting point. All of these Ni(II) complexes show great activity (up to 6 10 6 g of PE (mol ofNi) 1 h 1 ), exceptional thermal stability (stable at up to 100 C) and generate polyethylene withvery high molecular weight (M n up to 1.6 10 6 ) and very narrow molecular weight distribution.In the dibromo Ni(II) system, the electronic perturbations exhibit little variation on the ethylenepolymerization. In the Ni(acac) system, dramatic ligand electronic effects are observed in terms ofcatalytic activity and polyethylene molecular weight. Keywords: -diimine; Nickel; dibenzhydryl; ethylene polymerization; electronic effect; cocatalyst

The synthetic scope of photo-induced copper-mediated polymerization (photoCMP) in continuous-flow reactors is further explored. A series of monomers, namely, methyl (MA), ethyl (EA), n-butyl (nBA), 2-hydroxyethyl (HEA), and di(ethylene glycol) ethyl ether (DEGA) acrylate are investigated, all showing high livingness (dispersity in the range of 1.1 and linear first order kinetics) in the polymerizations and high conversions within 20-min reaction time. Next to the commonly used solvent (dimethyl sulfoxide [DMSO]), also a water-ethanol mixture was used as greener alternative, without any loss in reaction control. Upscaling the reactor from 2 to 16 mL allows for production of over 200 g of high-definition material (3000 g/mol, 1.1 dispersity) in overnight operation (18 h), demonstrating that the photoprocess can be run under very stable conditions even for extended reaction times. Via coupling of two reactors, direct chain extension of copolymers in a single reaction step is also demonstrated.

Benzaldehyde-functional cellulose paper sheets have been synthesized via tosylation of cellulose (Whatman No 5) followed by addition of p-hydroxy benzaldehyde. Via UV-induced Paterno-Büchi [2+2] cycloaddition reactions, these aldehyde functional surfaces are grafted with triallylcyanurate, trimethylolpropane allyl ether, and vinyl chloroacetate. In the following, allyl-functional polymers (poly(butyl acrylate), pBA, Mn = 6990 g mol(-1) , Đ = 1.12 and poly(N-isopropyl acrylamide), pNIPAAm, Mn = 9500 g mol(-1) , Đ = 1.16) synthesized via reversible addition fragmentation chain transfer polymerization are conjugated to the celloluse surface in a UV-induced grafting-to approach. With pBA, hydrophobic cellulose sheets are obtained (water contact angle 116°), while grafting of pNIPAAm allows for generation of "smart" surfaces, which are hydrophilic at room temperature, but that become hydrophobic when heated above the characteristic lower critical solution temperature (93° contact angle). The Paterno-Büchi reaction has been shown to be a versatile synthetic tool that also performs well in grafting-to approaches whereby its overall performance seems to be close to that of radical thiol-ene reactions.

The copolymerization of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-p-phenylene vinylene] (MDMO-PPV) with poly[2-methoxy-5-(carboxypentyloxy)-PPV] (CPM-PPV) and poly[2,5-dicyano-PPV] (CN-PPV) is studied and postpolymerization modification with water soluble substituents is demonstrated.

[Junkers, Thomas] Hasselt Univ, Polymer React Design Grp, Inst Mat Res IMO, Martelarenlaan 42, BE-3500 Hasselt, Belgium. [Junkers, Thomas] IMEC, Associated Lab IMOMEC, Wetenschapspk 1, BE-3590 Diepenbeek, Belgium. [Hoogenboom, Richard] Univ Ghent, Supramol Chem Grp, Dept Organ & Macromol Chem, Krijgslaan 281 S4 Bis, BE-9000 Ghent, Belgium.

Poly(p-phenylene vinylene)s (PPVs) are an important class of highly fluorescent polymeric semiconductor materials. Despite their somewhat declining use in optoelectronic applications, PPV synthesis routes were in recent years significantly improved towards controlled/living polymerization. In this way, nowadays well-defined PPV structures that can be implemented in advanced polymer structures have become accessible, finding a potential application in new fields of research. This review summarizes the advances made and the types of polymers that have recently become available. Most notably, two polymerization approaches are compared, living polymerization towards well-defined PPVs via ring-opening metathesis polymerization (ROMP) and chain-transfer radical and anionic polymerization in the so-called sulfinyl precursor polymerization route.

Molecularly imprinted polymers (MIPs) in the micron and submicron scale based on the bifunctional cross-linker N,O-bismethacryloylethanolamine (NOBE) have been synthesized using bulk and miniemulsion polymerization, respectively. MIPs with distinct selectivity for the template testosterone were obtained. Colloidal MIP particles made using the miniemulsion technique have significant advantages compared to bulk MIP counterparts owing to their small size, homogeneity, and increased surface, as is demonstrated by optical batch rebinding studies using a non imprinted polymer (NIP) as a negative control. Affinity and selectivity studies were also performed with the miniemulsion colloidal MIPs. These MIPs display largely increased imprint factors (6.8 vs 2.2) when compared to their bulk MIP counterparts. Further, selectivity studies by using analogue steroids show that colloidal MIPs also display a higher selectivity. In summary, miniemulsion MIPs show much better performance with respect to molecular recognition in aqueous solution, while providing at the same time the possibility for a water-based MIP synthesis.

Conjugated polymers have attracted significant interest in the bioimaging field due to their excellent optical properties and biocompatibility. Tailor-made poly(p-phenylenevinylene) (PPV) conjugated polymer nanoparticles (NPs) are in here described. Two different nanoparticle systems using poly[2-methoxy-5-(3',7'-dimethoxyoctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and a functional statistical copolymer 2-(5'-methoxycarbonylpentyloxy)-5-methoxy-1,4-phenylenevinylene (CPM-MDMO-PPV), containing ester groups on the alkoxy side chains, were synthesized by combining miniemulsion and solvent evaporation processes. The hydrolysis of ester groups into carboxylic acid groups on the CPM-MDMO-PPV NPs surface allows for biomolecule conjugation. The NPs exhibited excellent optical properties with a high fluorescent brightness and photostability. The NPs were in vitro tested as potential fluorescent nanoprobes for studying cell populations within the central nervous system. The cell studies demonstrated biocompatibility and surface charge dependent cellular uptake of the NPs. This study highlights that PPV-derivative based particles are a promising bioimaging probe and can cater potential applications in the field of nanomedicine.

The polymerization of cyclic phosphates to poly(phosphoester)s, PPEs, is optimized for chip-based microreactors under continuous flow conditions. The anionic ring-opening polymerization of 2-isobutyoxy-2-oxo-1,3,2-dioxaphospholane (iBP) via the use of two organocatalytic systems allowed to polymerize to nearly quantitative monomer conversion within 10 or 3 min, respectively at a reaction temperature of 40 degrees C. Further, the optimized polymerization protocol was applied to 2-butenoxy-2-oxo-1,3,2-dioxaphospholane (BP) which yields a polymer that carries an alkene functionality per monomer repeating unit. This material can be postmodified in an UV-induced radical thiol-ene reaction, which was also shown to proceed with very high efficiency under UV-flow conditions. Eventually, both reactions were coupled in a two-stage reactor setup, showing that the thermally-activated polymerization can be coupled with high efficiency to the UV-activated post-polymerization modification reaction. The introduced reactor setup can in the future be used to produce and screen a broad variety of functional PPE materials with various functionalities and physical properties. (C) 2016 Elsevier Ltd. All rights reserved.

An acid-induced cydohexanone/tert-butylhydroperoxide initiation system for ambient temperature reversible addition fragmentation transfer (RAFT) polymerization of vinyl monomers is presented. The reaction system is optimized for the synthesis of poly(n-butyl acrylate) of various chain length. The polymerization shows typical living characteristics and polymers with dispersities close to 1.1 are obtained. Analysis of the polymer end groups by means of soft ionization mass spectrometry reveals the typical distribution of polymer containing both R and Z RAFT end groups and a minor distribution of a RAFT polymer carrying a cyclohexanone end group in alpha position. This observation demonstrates that the polymerization is initiated solely by ketone radicals despite a relatively complex initiation mechanism that involves several intermediates. The room, temperature-derived homopolymers are successfully chain extended with tert-butyl acrylate resulting in well-defined block copolymer structures. To demonstrate the versatility of the approach, the room temperature RAFT polymerization is also applied to synthesize styrene and N-isopropylacrylamide, yielding best results for polystyrene. Finally, also a bisperoxide structure is tested as an alternative for the ketone/peroxide mixture. Polymerization proceeds substantially faster in this case and successful controlled polymerization to full conversion is achieved even at 0 degrees C. In general the proposed room temperature RAFT technique is very easy to carry out, in principle easily up scalable, metal free and shows high potential toward the synthesis of well-defined temperature sensitive materials.

For the first time, a 1000 Hz pulse laser has been applied to determine detailed kinetic rate coefficients from pulsed laser polymerization-size exclusion chromatography experiments. For the monomer tert-butyl acrylate, apparent propagation rate coefficients kp (app) have been determined in the temperature range of 0-80 °C. kp (app) in the range of few hundreds to close to 50 000 L·mol(-1) ·s(-1) are determined for low and high pulse frequencies, respectively. The apparent propagation coefficients show a distinct pulse-frequency dependency, which follows an S-shape curve. From these curves, rate coefficients for secondary radial propagation (kp (SPR) ), backbiting (kbb ), midchain radical propagation (kp (tert) ), and the (residual) effective propagation rate (kp (eff) ) can be deduced via a herein proposed simple Predici fitting procedure. For kp (SPR) , the activation energy is determined to be (17.9 ± 0.6) kJ·mol(-1) in excellent agreement with literature data. For kbb , an activation energy of (25.9 ± 2.2) kJ·mol(-1) is deduced.