Автоматизация научных исследований

We report the synthesis and characterization of a novel azobenzene-containing miktoarm star polymer AB3 (Mn=9700 gmol-1, M = 1.10) as well as its self-assembly properties in water. The miktoarm copolymer is composed of a hydrophobic azopolymer and three hydrophilic PEG arms (Mn = 600 g mol-1). The hydrophobic/hydrophilic ratio of the amphiphilic miktoarm polymer is 78/22, leading to the formation of stable polymeric vesicles in water evidenced via TEM and cryo-TEM imaging. The photoresponse of these vesicles has been investigated by irradiation with UV light (= 350-400 nm) causing the disruption of the self-assemblies. Encapsulation of both hydrophilic and hydrophobic fluorescent probes, i.e., Nile Red and Rhodamine B, and the use of light as an external stimulus to trigger the release of the probes have also been demonstrated. © 2014 American Chemical Society

A novel interpretation of measured and simulated PLP data

Figure 1 - Simulated ν dependency of the observed kp in vinyl acetate PLP at 323 K. Case 1 (♦): chain length independent head-to-tail prop., Case 2 (■): chain length dependent head-to-tail prop., Case 3 (●): chain length dependent head-to-tail, head-to-head, tail-to-tail, and tail-to-head prop., and Case 4 (▲): Case 3 with backbiting by head and tail radicals, and mid-chain prop. Pulsed laser polymerization (PLP) is an interesting technique to study individual reactions.1-4 In PLP, photoinitiator radical fragments are generated at laser pulses with a frequency ν (or dark time Δt = ν-1). Depending on the PLP conditions and the monomer type, the molar mass distribution (MMD) can possess specific characteristics, allowing the determination of intrinsic rate coefficients. Most known is that under well-chosen conditions a multimodal MMD with inflection points Lj (j = 1, 2, …) is obtained, allowing the determination of the propagation rate coefficient kp ([M]0: initial monomer concentration): (1) In this contribution, kinetic Monte Carlo (kMC) modeling is applied to allow a further understanding and exploitation of PLP. For PLP of acrylates, regression analysis to low frequency inflection point data at various solvent volume fractions is proposed as an additional new method to estimate the backbiting rate coefficient kbb.5 Moreover, it is demonstrated that photodissociation, chain initiation and termination reactivities can be extracted from the complete PLP MMD.6 For the first time, the ratio of MMD peak heights has been used for the fast and reliable estimation of the photodissociation quantum yield,Φ.7 For PLP of vinyl acetate a unique combination of ab initio calculated rate coefficients and kMC simulations is considered to explain the experimental8 ν dependency of the observed kp (cf. Case 4 in Figure 1; Eq. (1) with kpobs). Via a stepwise extension of the kMC model (cf. 4 cases in Figure 1), the ν dependency is attributed to backbiting of tail radicals formed via head-to-head propagation.9 In contrast to acrylates, backbiting of head radicals is shown to be kinetically insignificant in VAc PLP, further highlighting the chemical difference between both vinyl monomer types. Please click Additional Files below to see the full abstract

Versatile Synthesis of Stable, Functional Polypeptides via Reaction with Epoxides

Methodology was developed for efficient alkylation of methionine residues using epoxides as a general strategy to introduce a wide range of functional groups onto polypeptides. Use of a spacer between epoxide and functional groups further allowed addition of sterically demanding functionalities. Contrary to other methods to alkylate methionine residues, epoxide alkylations allow the reactions to be conducted in wet protic media and give sulfonium products that are stable against dealkylation. These functionalizations are notable since they are chemoselective, utilize stable and readily available epoxides, and allow facile incorporation of an unprecedented range of functional groups onto simple polypeptides using stable linkages

Nitrosocarbonyl Hetero-Diels–Alder Cycloaddition: A New Tool for Conjugation

It is demonstrated that nitrosocarbonyl hetero-Diels-Alder chemistry is an efficient and versatile reaction that can be applied in macromolecular synthesis. Polyethylene glycol functionalized with a hydroxamic acid moiety undergoes facile coupling with cyclopentadiene-terminated polystyrene, through a copper-catalyzed as well as thermal hetero-Diels-Alder reaction. The mild and orthogonal methods used to carry out this reaction make it an attractive method for the synthesis of block copolymers. The resulting block copolymers were analyzed and characterized using GPC and NMR. The product materials could be subjected to thermal retro [4 + 2] cycloaddition, allowing for the liberation of the individual polymer chains and subsequent recycling of the diene-terminated polymers. © 2014 American Chemical Society

Diels-Alder reactions for carbon material synthesis and surface functionalization

To meet the ever growing demand for carbon nanomaterials with tailored properties, Diels-Alder reactions are emerging as an efficient alternative to other synthetic methods. From an application perspective, the development of convenient surface functionalization strategies for carbon nanostructures is of paramount importance. Pristine carbon nanostructures display a natural tendency to undergo Diels-Alder reactions with a range of functional dienes and dienophiles without the need of a catalyst. This has sparked significant scientific interest in exploiting the Diels-Alder reaction as a powerful strategy for their synthesis as well as for their subsequent surface functionalization. The present review highlights the remarkable role of Diels-Alder reactions for the synthesis of fullerenes, carbon nanotubes and graphene, and its promise as a facile carbon nanostructure functionalization strategy with small molecules and polymer chains. A critical overview of the recent developments evidencing the potential of Diels-Alder reactions as an efficient route to carbon based functional materials is presented. © 2013 The Royal Society of Chemistry

Living radical polymerization of ethylene: A challenge overcome?

It's alive! A significant step forward in the controlled radical polymerization of ethylene through the reversible addition–fragmentation chain‐transfer process was reported recently by Monteil and co‐workers. Control over molecular weight, dispersity of the molecular weight distribution, and polymer end groups were investigated. DMC=Dimethyl carbonate