A series of nonionic, anionic, and cationic water-soluble monomers bearing the (meth)acrylate, (meth)acrylamide, or styrene moiety were polymerized in water by free-radical polymerization
via reversible addition−fragmentation chain transfer (RAFT). Several new water-soluble RAFT agents
based on dithiobenzoate were employed that are water soluble independently of the pH. One of them
bears a fluorophore, enabling unsymmetrical double end-group labeling as well as the preparation of
fluorescent-labeled polymers. The temperature-dependent stability of the new RAFT agents against
hydrolysis was studied. Controlled polymerization in aqueous solution was possible with styrenic, acrylic,
and methacrylic monomers; molar masses increase with conversion, and polydispersities are relatively
low. But RAFT polymerization failed for an anionic itaconate. Whereas polymerizations of methacrylamides
were slow at temperatures below 60 °C, such conditions proved favorable for the RAFT polymerization
of acrylates and methacrylates, to minimize hydrolysis of the dithioester end-group functionality, and to
improve the preparation of block copolymers.
Multifunctional chain transfer agents for RAFT polymerisation were designed for the one-step synthesis of amphiphilic star polymers. Thus, hydrophobically end-capped 3-and 4-arm star polymers, as well as linear ones for reference, were made of the hydrophilic monomer N,N-dimethylacrylamide (DMA) in high yield with molar masses up to 150 000 g mol
À1, narrow molar mass distribution (PDI # 1.2) and high end group functionality ($90%). The associative telechelic polymers form transient networks of interconnected aggregates in aqueous solution, thus acting as efficient viscosity enhancers and rheology modifiers, eventually forming hydrogels. The combination of dynamic light scattering (DLS), small angle neutron scattering (SANS) and rheology experiments revealed that several molecular parameters control the structure and therefore the physical properties of the aggregates. In addition to the size of the hydrophilic block (maximum length for connection) and the length of the hydrophobic alkyl chain ends (stickiness), the number of arms (functionality) proved to be a key parameter.
The aim of this work was the synthesis of starch macroinitiators for cationic polymer grafted starches that: W are free of cationic homopolymer, and (ii) display a high degree of conversion of the cationic monomer. We show that this can be achieved by a free-radical polymerization reaction using the cationic monomer N-methaeryloyloxyethyl-N,N-dimethyl-N-benzylammonium chloride (XLADAM-BQ) and a new starch-based macroazoinitiator. For this purpose, the acid chloride of 4-tert-butylazo-4-cyanovaleric acid was synthesized and bound covalently to starch (predominantly in the C6 position) to form a nonsymmetrically substituted macroinitiator that was used to polymerize MADAM-BQ in aqueous media. Essentially no MADAM-BQ homopolymer was formed. The initiator decomposes thermally to starch radicals of high reactivity and low-molar mass radicals that do not initiate polymerization. The reason for the different reactivities of the radicals is presumably due to the nonsymmetric constitution of the starch-bound azo groups. The graft polymerization of MADAM-BQ in aqueous solution performs according to an ideal overall kinetic. The structure of the synthesized starch-graft-poly(MADAM-BQ) products is similar to that of block copolymers because of the low radical efficiency of the starch initiators in aqueous solution. Especially, starch substrates with a higher content of azo groups did not lead to graft products with shorter graft distances because the state of solution of these macroinitiators becomes worse and aggregation occurs with an increasing degree of substitution
Microprocess engineering is an alternative approach to design reactors for CO2 methanation, which are used in power‐to‐gas applications. Microreactors offer advantages, e.g., in terms of heat removal. In the present work, design criteria evolved from transport phenomena are applied to derive preliminary reactor dimensions. The developed 1D model is used for parametric studies and reveals heat transport as limiting factor. More detailed 3D models confirm the results and demonstrate the effect of the metal matrix on heat transport. For further optimization a multi‐stage reactor design is proposed.
The analysis of the porosity of materials is an important and challenging field in analytical chemistry. The gas adsorption and mercury intrusion methods are the most established techniques for quantification of specific surface areas, but unfortunately, dry materials are mandatory for their applicability. All porous materials that contain water and other solvents in their functional state must be dried before analysis. In this process, care has to be taken since the removal of solvent bears the risk of an incalculable alteration of the pore structure, especially for soft materials. In the present paper, we report on the use of small-angle X-ray scattering (SAXS) as an alternative analysis method for the investigation of the micro and mesopores within cellulose beads in their native, i.e., water-swollen state; in this context, they represent a typical soft material. We show that even gentle removal of the bound water reduces the specific surface area dramatically from 161 to 109 m(2) g(-1) in cellulose bead sample type MT50 and from 417 to 220 m(2) g(-1) in MT100. Simulation of the SAXS curves with a bimodal pore size distribution model reveals that the smallest pores with radii up to 10 nm are greatly affected by drying, whereas pores with sizes in the range of 10 to 70 nm are barely affected. The SAXS results were compared with Brunauer-Emmett-Teller results from nitrogen sorption measurements and with mercury intrusion experiments.
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