Polystyrene-b-poly(tert-butyl acrylate) and polystyrene-b-poly(acrylic acid) dendrimer-like copolymers: two-dimensional self-assembly at the air-water interface

The two-dimensional self-assembly at the air/water (A/W) interface of two dendrimer-like copolymers based on polystyrene and poly(tert-butyl acrylate) (PS-b-PtBA) or poly(acrylic acid) (PS-b-PAA) was investigated through surface pressure measurements (isotherms, isochores, and compression-expansion hysteresis experiments) and atomic force microscopy (AFM) imaging. The two dendrimer-like block copolymers have an 8-arm PS core (Mn = 10 000 g/mol, approximately 12 styrene repeat units per arm) with a 16-arm PtBA (Mn = 230 000 g/mol, approximately 112 tert-butyl acrylate repeat units per arm) or PAA (Mn = 129 000 g/mol, approximately 112 acrylic acid repeat units per arm) corona. The PS-b-PtBA sample forms stable Langmuir monolayers and aggregates into circular surface micelles up to a plateau observed in the corresponding isotherm around 24 mN/m. Beyond this threshold, the monolayers collapse above the interface, resulting in the formation of large and irregular desorbed aggregates. The PS-b-PAA sample has ionizable carboxylic acid groups, and its A/W interfacial self-assembly was therefore investigated for various subphase pH values. Under basic conditions (pH = 11), the carboxylic acid groups are deprotonated, and the PS-b-PAA sample is therefore highly water-soluble and does not form stable monolayers, instead irreversibly dissolving in the aqueous subphase. Under acidic conditions (pH = 2.5), the PS-b-PAA sample is less water-soluble and becomes surface-active. The pseudoplateau observed in the isotherm around 5 mN/m corresponds to a pancake-to-brush transition with the PAA chains dissolving in the water subphase and stretching underneath the anchoring PS cores. AFM imaging revealed the presence of circular surface micelles for low surface pressures, whereas the biphasic nature of the pseudoplateau region was confirmed with the gradual aggregation of the micellar PS cores above the PAA chains. The aggregation numbers for both samples were estimated around 3-5 dendrimer-like copolymers per circular surface micelle. These rather low values confirmed the tremendous influence of molecular architecture on the two-dimensional self-assembly of block copolymers.     

Radical polymerization and preliminary microbiological investigation of new polymer derived from myrtenol

A new methacrylic monomer derived from myrtenol, an essential oil possessing biocidal properties extracted from Myrtus communis L., was prepared in one step and named myrtenyl methacrylate. Conventional radical polymerization was performed in solution with 2,2′-azobis(2-methylpropionitrile) as thermal initiator in the temperature range 60–80 °C. Influences of reaction time, temperature and initiator concentration on monomer conversion and molar masses were studied. Controlled radical polymerization experiments were performed using the Atom Transfer Radical Polymerization techniques, leading to the formation of polymers with controlled molar masses and narrow molar mass distribution. Microbiological tests of these (macro)molecules were carried out using planktonic and adhesion tests with gram-positive and gram-negative bacteria in order to evaluate their antibacterial properties.     

Chemical surface modification of poly(ethylene terephthalate) fibers by aminolysis and grafting of carbohydrates

PET is a semicrystalline thermoplastic polyester used in many fields. For a variety of applications, however, it is necessary to impart desired properties by introducing specific functional groups on the surface. Aminolysis of PET fibers with diamines (1,2-diaminoethane, 1,6-diaminohexane, 3,6-dioxa-1,8-diaminooctane, and 4,9-dioxa-1,12-diaminododecane) gives amino functional groups on the surface. The effects of temperature, reaction time, diamine concentration, and solvent employed for the grafting were studied. The graft yield was observed to increase with temperature, reaction time, and diamine concentration. Aminolysis affects greatly the geometry and surface morphology of PET fibers as observed by scanning electronic microscopy and atomic force microscopy in tapping mode. A decrease of fibers diameter and an increase of surface heterogeneity and roughness due to chemical degradation is observed. Amino groups on the surface were used to prepare glycosylated fibers by reductive amination or amidation with different carbohydrates as maltose, maltotriose, and maltohexaose. The study reveals that the yield is dependent on the initial amino groups' surface concentration and the molar mass of the carbohydrate. These surfaces could benefit to a wide range of applications in the biomedical field. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2172–2183, 2007     

Synthesis of multicyclic and grafted polystyrenes

Well‐defined multicyclic polystyrenes are prepared in two steps. The first step is the preparation of a cyclic difunctional polystyrene by the reaction of α,ω‐dilithiopolystyrene chains with 1,3‐bis(phenylethenyl)benzene. Then, this product is covalently grafted to poly(chloromethylstyrene) chains leading to the formation of a high molar mass product containing linear and cyclic parts. As a model reaction and to optimize the previous reaction, a study of coupling of the linear difunctional model polystyrene with poly(chloromethylstyrene) is performed leading to grafted polystyrene. The grafted products are analyzed by size‐exclusion chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, and liquid chromatography at the exclusion‐adsorption transition point. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2723–2730, 2001     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Synthesis and Photoreaction of a-Methylene-γ-Butyrolactone-Psoralen Heterodimers

Three double-headed molecules were synthesized by linking a photoreactive linear (1, 2) or angular (3) furocou-marin via a linear 10- or 5-carbon chain to an electro-philic α-methylene-γ-butyrolactone. The photochemical behavior of these molecules was investigated in ethanol at 365 nm and the photocycloadducts obtained from each compound were isolated and characterized. In all cases, the photoreactivity results showed the 3,4-pyrone double bond of the psoralen (linear or angular) to be the most reactive and [2 + 2] intramolecular photocycloadducts between the 3,4-pyrone and the exomethylenic double bonds were obtained. With compounds 1 and 2, two kinds of intramolecular photocycloadducts were obtained, namely cissyn-exo derivatives in 46% and 36% yield, respectively, and trans-syn-exo derivatives in 14% and 18% yield, respectively. With compound 3, only the trans-syn-exo derivative was obtained in 33% yield.     

CNSL,a Promising Building Blocks for Sustainable Molecular Design of Surfactants: A Critical Review

Surfactants are crystallizing a certain focus for consumer interest, and their market is still expected to grow by 4 to 5% each year. Most of the time these surfactants are of petroleum origin and are not often biodegradable. Cashew Nut Shell Liquid (CNSL) is a promising non-edible renewable resource, directly extracted from the shell of the cashew nut. The interesting structure of CNSL and its components (cardanol, anacardic acid and cardol) lead to the synthesis of biobased surfactants. Indeed, non-ionic, anionic, cationic and zwitterionic surfactants based on CNSL have been reported in the literature. Even now, CNSL is absent or barely mentioned in specialized review or chapters talking about synthetic biobased surfactants. Thus, this review focuses on CNSL as a building block for the synthesis of surfactants. In the first part, it describes and criticizes the synthesis of molecules and in the second part, it compares the efficiency and the properties (CMC, surface tension, kraft temperature, biodegradability) of the obtained products with each other and with commercial ones.     

Long-range ordering in the Bi1−xAexFeO3−x/2 perovskites: Bi1/3Sr2/3FeO2.67 and Bi1/2Ca1/2FeO2.75

Two-ordered perovskites, Bi_1/3Sr_2/3FeO_2.67 and Bi_1/2Ca_1/2FeO_2.75, have been stabilized and characterized by transmission electron microscopy, Mössbauer spectroscopy and X-ray powder diffraction techniques. They both exhibit orthorhombic superstructures, one with a≈b≈2a_p and c≈3a_p (S.G.: Pb2n or Pbmn) for the Sr-based compound and one with a≈b≈2a_p and c≈8a_p (S.G.: B222, Bmm2, B2mm or Bmmm) for the Ca-based one. The high-resolution transmission electron microscopy (HRTEM) images evidence the existence of one deficient [FeO_x]_∞ layer, suggesting that Bi_1/3Sr_2/3FeO_2.67 and Bi_1/2Ca_1/2FeO_2.75 behave differently compared to their Ln-based homolog. The HAADF-STEM images allow to propose a model of cation ordering on the A sites of the perovskite. The Mössbauer analyses confirm the trivalent state of iron and its complex environment with three types of coordination. Both compounds exhibit a high value of resistivity and the inverse molar susceptibility versus temperature curves evidence a magnetic transition at about 730 K for the Bi_1/3Sr_2/3FeO_2.67 and a smooth reversible transition between 590 and 650 K for Bi_1/2Ca_1/2FeO_2.75.     

Moderate pressure synthesis of rare earth nickelate with metal-insulator transition using polymeric precursors

Rare earth nickelates exhibit a reversible metal-semiconductor phase transition that is, in the infrared range, responsible for a thermo-optical contrast. The state of the art synthesis of these compounds usually requires high oxygen pressure to stabilize Ni in the oxidation state 3⁺. In this work, using polymeric precursor associated with moderate pressure annealing, we show that it is possible to obtain fully oxidized rare earth nickelate with metal-insulator transition. Using thermogravimetric analysis, X-ray diffraction and transmission electronic microscopy we compare different samples synthesized at different oxygen pressures and demonstrate their structural similarity. Thermo-optical properties were measured, in the infrared range, using reflectance measurements and confirmed the metal-insulator transition at 60 °C in both samples.TEM observations lead to the conclusion that the structure commonly obtained at 175 bar is perfectly observed in the 20 bar sample without major structural defects. The two samples exhibit a thermochromic behavior and thermo-optical properties of the two samples are equivalent.