Dispersion of polymer-grafted magnetic nanoparticles in homopolymers and block copolymers

The dispersion of magnetic nanoparticles (NPs) in homopolymer poly(methyl methacrylate) (PMMA) and block copolymer poly(styrene-b-methyl methacrylate) (PS-b-PMMA) films is investigated by TEM and AFM. The magnetite (Fe3O4) NPs are grafted with PMMA brushes with molecular weights from M = 2.7 to 35.7 kg/mol. Whereas a uniform dispersion of NPs with the longest brush is obtained in a PMMA matrix (P = 37 and 77 kg/mol), NPs with shorter brushes are found to aggregate. This behavior is attributed to wet and dry brush theory, respectively. Upon mixing NPs with the shortest brush in PS-b-PMMA, as-cast and annealed films show a uniform dispersion at 1 wt%. However, at 10 wt%, PS-b-PMMA remains disordered upon annealing and the NPs aggregate into 22 nm domains, which is greater than the domain size of the PMMA lamellae, 18 nm. For the longest brush length, the NPs aggregate into domains that are much larger than the lamellae and are encapsulated by PS-b-PMMA which form an onion-ring morphology. Using a multi-component Flory–Huggins theory, the concentrations at which the NPs are expected to phase separate in solution are calculated and found to be in good agreement with experimental observations of aggregation

Emulsion Polymerization of Dihydroeugenol-, Eugenol-, and Isoeugenol-Derived Methacrylates

International audienc

Poly(fluoroacrylate)s with tunable surface hydrophobicity via radical copolymerization of 2,2,2-trifluoroethyl α-fluoroacrylate and 2-(trifluoromethyl)acrylic acid

International audienceThe synthesis of poly(fluoroacrylate)s with tunable wettability and improved adhesion for potential applicationas functional coatings was achieved via radical copolymerization of 2,2,2-trifluoroethylα-fluoroacrylate (FATRIFE) with 2-(trifluoromethyl)acrylic acid (MAF), an adhesion-promoting monomer.These copolymerizations, initiated by tert-butyl peroxypivalate at varying comonomer feed ([FATRIFE]0/[MAF]0) ratios led to a series of poly(FATRIFE-co-MAF) copolymers with different molar compositions infair to good conversions (32–87%) depending on the MAF feed content. The microstructures of the synthesizedpoly(FATRIFE-co-MAF) copolymers were determined by 19F NMR spectroscopy. Even at MAFfeed contents higher than 50%, MAF incorporation into the copolymers was lower than 50%, since MAFdoes not undergo any homopolymerization under radical polymerization conditions. The reactivity ratiosof the (FATRIFE; MAF) monomer pair were also determined (rFATRIFE = 1.65 ± 0.07 and rMAF = 0 at 56 °C)evidencing the formation of statistical copolymers. Initiation involving a highly branched perfluorinatedradical that released a •CF3 radical enabled the demonstration of the regioselective attack of the latterradical onto the CH2 of FATRIFE. The resulting poly(FATRIFE-co-MAF) copolymers exhibited various glasstransition temperatures (Tgs) depending on their compositions. Tg values increased with increasing MAFcontents in the copolymer. In addition, their thermal stability (the temperature for 10% weight loss in air,Td10%) increased with increasing FATRIFE content in the copolymer and reached 348 °C (for that containing93 mol% FATRIFE). Finally, a high copolymer MAF content led to both a good adhesion onto metalsubstrates and to improved hydrophilicity, as revealed by the decrease of the water contact angle from107° (for a reference PFATRIFE homopolymer) to 81° (for a copolymer containing 42 mol% MAF)

Micromechanics of root development in soil

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Fluorinated nanotubes : synthesis and self-assembly of cyclic peptide–poly(vinylidene fluoride) conjugates

The synthesis of cyclic peptide–poly(vinylidene fluoride) (CP–PVDF) conjugates comprising (D-alt-L)-cyclopeptides as building blocks and their self-assembly into tube-like structures is described. By growing two PVDF polymeric chains from opposite sides of a preassembled cyclic-peptide macro-chain transfer agent, a PVDF–CP–PVDF conjugate was prepared. This “grafting-from” strategy, allowed the synthesis of the conjugate with high purity and using facile purification steps. The controlled self-assembly of the conjugate from DMF or DMSO solutions was carried out by addition of THF. This triggered the aggregation process that led to formation of tube-like structures. The mean length and width of the PVDF–CP–PVDF tubes were measured using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Surprisingly, the self-assembly of the CP–PVDF conjugates in DMF/THF allowed the preparation of long (up to 25 μm) tube-like structures. The formation of such long tubular peptide–polymer aggregates, based on the stacking of cyclopeptides, is unprecedented and is believed to rely on synergetic effects between the stacking of the cyclic peptide and the interactions of the fluoropolymer–peptide conjugates

Neighboring Group Participation and Internal Catalysis Effects on Exchangeable Covalent Bonds: Application to the Thriving Field of Vitrimer Chemistry

Vitrimers constitute a fascinating class of polymer materials that make the link between the historically opposed 3D networks (thermosets) and linear polymers (thermoplastics). Their chemical resistance, reshaping ability, and unique rheological behavior upon heating make them promising for future applications in industry. However, many vitrimers require the use of high catalyst loadings, which raises concerns for their durability and limits their potential applications. To cope with this issue, internal catalysis and neighboring group participation (NGP) can be used to enhance the reshaping ability of such materials. A few studies report the effect of activating groups on the exchange reactions in vitrimers. Nevertheless, knowledge on this topic remains scarce, although research on vitrimers would greatly benefit from NGP already known in organic chemistry. The present Perspective presents the different types of exchangeable bonds implemented in vitrimers and discusses chemical groups known to have or potentially capable of an enhancing effect on exchange reactions. This analysis is underpinned by a thorough mechanistic discussion of the various exchangeable bonds presented

Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution

Reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate was used to prepare three poly(glycerol monomethacrylate)x–poly(2-hydroxypropyl methacrylate)y (denoted Gx-Hy or PGMA-PHPMA) diblock copolymers, namely G37-H80, G54-H140, and G71-H200. A master phase diagram was used to select each copolymer composition to ensure that a pure worm phase was obtained in each case, as confirmed by transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) studies. The latter technique indicated a mean worm cross-sectional diameter (or worm width) ranging from 11 to 20 nm as the mean degree of polymerization (DP) of the hydrophobic PHPMA block was increased from 80 to 200. These copolymer worms form soft hydrogels at 20 °C that undergo degelation on cooling. This thermoresponsive behavior was examined using variable temperature DLS, oscillatory rheology, and SAXS. A 10% w/w G37-H80 worm dispersion dissociated to afford an aqueous solution of molecularly dissolved copolymer chains at 2 °C; on returning to ambient temperature, these chains aggregated to form first spheres and then worms, with the original gel strength being recovered. In contrast, the G54-H140 and G71-H200 worms each only formed spheres on cooling to 2 °C, with thermoreversible (de)gelation being observed in the former case. The sphere-to-worm transition for G54-H140 was monitored by variable temperature SAXS: these experiments indicated the gradual formation of longer worms at higher temperature, with a concomitant reduction in the number of spheres, suggesting worm growth via multiple 1D sphere–sphere fusion events. DLS studies indicated that a 0.1% w/w aqueous dispersion of G71-H200 worms underwent an irreversible worm-to-sphere transition on cooling to 2 °C. Furthermore, irreversible degelation over the time scale of the experiment was also observed during rheological studies of a 10% w/w G71-H200 worm dispersion. Shear-induced polarized light imaging (SIPLI) studies revealed qualitatively different thermoreversible behavior for these three copolymer worm dispersions, although worm alignment was observed at a shear rate of 10 s–1 in each case. Subsequently conducting this technique at a lower shear rate of 1 s–1 combined with ultra small-angle x-ray scattering (USAXS) also indicated that worm branching occurred at a certain critical temperature since an upturn in viscosity, distortion in the birefringence, and a characteristic feature in the USAXS pattern were observed. Finally, SIPLI studies indicated that the characteristic relaxation times required for loss of worm alignment after cessation of shear depended markedly on the copolymer molecular weight

Synthesis and characterization of poly(amino acid methacrylate)-stabilized diblock copolymer nano-objects

Amino acids constitute one of Nature's most important building blocks. Their remarkably diverse properties (hydrophobic/hydrophilic character, charge density, chirality, reversible cross-linking etc.) dictate the structure and function of proteins. The synthesis of artificial peptides and proteins comprising main chain amino acids is of particular importance for nanomedicine. However, synthetic polymers bearing amino acid side-chains are more readily prepared and may offer desirable properties for various biomedical applications. Herein we describe an efficient route for the synthesis of poly(amino acid methacrylate)stabilized diblock copolymer nano-objects. First, either cysteine or glutathione is reacted with a commercially available methacrylate-acrylate adduct to produce the corresponding amino acid-based methacrylic monomer (CysMA or GSHMA). Well-defined water-soluble macromolecular chain transfer agents (PCysMA or PGSHMA macro-CTAs) are then prepared via RAFT polymerization, which are then chain-extended via aqueous RAFT dispersion polymerization of 2-hydroxypropyl methacrylate. In situ polymerization-induced self-assembly (PISA) occurs to produce sterically-stabilized diblock copolymer nano-objects. Although only spherical nanoparticles could be obtained when PGSHMA was used as the sole macro-CTA, either spheres, worms or vesicles can be prepared using either PCysMA macro-CTA alone or binary mixtures of poly(glycerol monomethacrylate) (PGMA) with either PCysMA or PGSHMA macro-CTAs. The worms formed soft free-standing thermo-responsive gels that undergo degelation on cooling as a result of a worm-to-sphere transition. Aqueous electrophoresis studies indicate that all three copolymer morphologies exhibit cationic character below pH 3.5 and anionic character above pH 3.5. This pH sensitivity corresponds to the known behavior of the poly(amino acid methacrylate) steric stabilizer chains