Controlled synthesis of poly(neopentyl p-styrene sulfonate) via reversible addition-fragmentation chain transfer polymerisation

The controlled synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) using RAFT polymerisation has been studied. Selected experimental conditions led to the production of PNSS with variable molecular weights and low dispersities (D{stroke}≤1.50). The controlled synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) using reversible addition-fragmentation chain transfer polymerisation has been studied under a wide range of experimental conditions. PNSS can be used as an organic-soluble, thermally labile precursor for industrially valuable poly(p-styrene sulfonate), widely employed in technologies such as ionic exchange membranes and organic electronics. The suitability of two different chain transfer agents, three solvents, three different monomer concentrations and two different temperatures for the polymerisation of neopentyl p-styrene sulfonate is discussed in terms of the kinetics of the process and characteristics of the final polymer. Production of PNSS with systematically variable molecular weights and low dispersities (D{stroke} ≤1.50 in all cases) has been achieved using 2-azidoethyl 2-(dodecylthiocarbonothioylthio)-2-methylpropionate in anisole at 75°C, with an initial monomer concentration of 4.0molL-1. Finally, a poly(neopentyl p-styrene sulfonate)-b-polybutadiene-b-poly(neopentyl p-styrene sulfonate) (PNSS-b-PBD-b-PNSS) triblock copolymer has been synthesised via azide-alkyne click chemistry. Moreover, subsequent thermolysis of the PNSS moieties generated poly(p-styrene sulfonate) end blocks. This strategy allows the fabrication of amphiphilic copolymer films from single organic solvents without the need for post-deposition chemical treatment

Photophysical processes and photochemical reactions involved in poly (N-vinylcarbazole) and in copolymers with carbazole units.

LPMM UMR CNRS-UBP 6505 Université Blaise Pascal Clermont-Ferrand (63) et StateUniversity of Moldova Kishinev (Moldavie).This paper is devoted to the analysis of the photochemical behaviour of copolymers with carbazole units exposed to long-wavelength radiation. These copolymers are constitued of two types of carbazolylethyl methracrylate units (CEM) with octyl methacrylate moieties (OMA). The exposure of copolymers and PVK to UV light results in dramatic modifications of the physical and photophysical properties of the polymer. These modifications can be correlated with modifications of the chemical structure of the matrix. The photoageing of copolymers and PVK has been analysed by fluorescence, ESR, UV-vis and infrared spectroscopies. The effects of crosslinking and chain scissions were determined by gel fraction measurements and size exclusion chromotography

Multi-scale analysis of hypochlorite induced PES/PVP ultrafiltration membranes degradation

In drinking water production plants, the use of oxidants such as sodium hypochlorite during in-place cleanings may impair the membrane integrity and radically impact the ultrafiltration process efficiency, leading to potential contamination of the permeate water with pathogens. This study investigates the effects of hypochlorite exposure on the properties of a commercially available UF hollow fiber. Mechanical performances and water permeability appeared to be greatly affected by the contact with hypochlorite. Monitoring them olecular changes by X-rayphoto electron spectroscopy (XPS), attenuated total reflectance infraredspectroscopy (ATR-IR), size exclusion chromatography (SEC) and VITA-mode atomic forcemicroscopy (VITA-AFM) revealed high stability of the main polymer constituting the membrane (i.e. polyethersulfone (PES)) and very high reactivity of the additive (i.e. poly (N-vinyl pyrrolidone (PVP)) towards immersion in aqueous sodium hypochlorite solution with maximal reaction rate for neutral to slightly basic pH. Correlation of those results unexpectedly leads to the conclusion that the over all membrane properties changes are governed by the additive fate

Design, synthesis and thermal behaviour of a series of well-defined clickable and triggerable sulfonate polymers

In the printing industry, the exploitation of triggerable materials that can have their surface properties altered on application of a post-deposition external stimulus has been crucial for the production of robust layers and patterns. To this end, herein, a series of clickable poly(R-alkyl p-styrene sulfonate) homopolymers, with systematically varied thermally-labile protecting groups, has been synthesised via reversible addition-fragmentation chain transfer (RAFT) polymerisation. The polymer range has been designed to offer varied post-deposition thermal treatment to switch them from hydrophobic to hydrophilic. Suitable RAFT conditions have been identified to produce well-defined homopolymers (Đ, Mw/Mn 80% for all but one monomer) with controllable molar mass. Poly(p-styrene sulfonate) with an isobutyl protecting group has been shown to be the most readily thermolysed polymer that remains stable at room temperature, and was thus investigated further by incorporation into a diblock copolymer, P3HT-b-PiBSS, by click chemistry. The strategy for preparation of thermal modifiable block copolymers exploiting R-protected p-styrene sulfonates and azide-alkyne click chemistry presented herein allows the design of new, roll-to-roll processable materials for potential application in the printing industry, particularly organic electronics

Radiochemical ageing of ethylene-propylene-diene elastomers. 4. Evaluation of some anti-oxidants.

Editeur ELSEVIERThe preceding papers of this series were devoted to the identification and quantification of the main chemical changes resulting front the radiochemical ageing of EPDM (77.9% ethylene, 21.4% propylene, 0.7% diene) and EPR (76.6% ethylene, 23.4% propylene) films irradiated under oxygen atmosphere using 6°Co Y-rays. It was shown that two processes are involved in the EPDM radio-oxidation. The random y-radiolysis of the polymer provides a constant source of macro-alkyl radicals that are likely to initiate a selective oxidation of the polymer through free-radicals reactions involving the abstraction of labile hydrogen atouts. In the present paper, infrared spectroscopy bas been used to study the y-degradation of EPDM cross-linked with dicumyl peroxide and/or stabilised with two types of anti-oxidants (hindered phenol or amine-type). The results show that the anti-oxidants are not efficient in preventing oxidation. To understand the lack of efficiency of the stabilisers, the impacts of the various formulations on the rate of degradation of EPDM against chain oxidation involved in thermal and UV ageing were also studied

Structural modifications of polymers under the impact of fast neutrons

International audienceFast neutron irradiations were performed at room temperature on a series of 13 polymer matrixes having great practical and academic interest. Polymers were irradiated with very low doses of 14 MeV neutrons deposited at reduced dose rate. The modifications of chemical structure of the polymeric matrixes resulting from irradiation were analyzed at the molecular scale by infrared and UV-visible spectroscopy. Particular attention was given to the oxidation occurring in irradiated matrixes during storage in the absence of light at room temperature. In addition the effects of irradiation on the chain arrangements in the polymers were analyzed by Differential Scanning Calorimetry. The most significant result obtained in this preliminary work was evidence that neutron irradiation with very low doses in the range ≈130-320 cGy could provoke structural changes. Indeed, depending on the matrixes, the formation of oxidation products along the macromolecular chains or the evolution of the polymer architecture, evidenced by changes of the Tg or of the crystallinity, was observed. The perspectives of this preliminary work are discussed

Analyse multi-échelle de la dégradation de membranes polymères d'ultrafiltration au contact de l'hypochlorite de sodium

Ce travail est consacré à l étude de l impact des lavages chimiques à l hypochlorite de sodium (NaOCl) effectués sur des membranes polymères polyéthersulfone (PES)/polyvinylpyrolidonne (PVP) (95%/5%) utilisées pour la filtration de l eau ou du lait. Sur les sites d exploitation les lavages chimiques sont nécessaires pour maintenir les propriétés de filtration des membranes qui se colmatent au cours de leur utilisation. L objectif de cette étude est de déterminer les mécanismes de dégradation de ces deux polymères au contact de l agent nettoyant, puis de corréler ces évolutions aux changements de propriétés macroscopiques des membranes en réalisant une analyse multi-échelle. Dans un premier temps, l étude de l impact de NaOCl sur des polymères modèles, le PES d une part et la PVP d autre part, a montré que la PVP s oxyde lorsqu elle est dissoute dans NaOCl ce qui n est pas le cas de films de PES. A partir de l identification des produits d oxydation, un mécanisme d oxydation radicalaire de la PVP mettant en jeu les radicaux hydroxyles provenant de la solution de NaOCl a été proposé. Dans un deuxième temps, afin de s affranchir de l hétérogénéité des membranes PES/PVP, des films de mélanges modèles PES/PVP à différents pourcentages de PVP ont été préparés. Leur immersion dans une solution de NaOCl provoque non seulement l oxydation de la PVP mais aussi celle du PES montrant sans ambiguïté l effet pro-dégradant de la PVP sur le PES. Dans un troisième temps, il a été montré que le vieillissement des membranes PES/PVP peut être explicité à partir des résultats obtenus sur les mélanges modèles, et que l évolution de la structure chimique de la PVP pouvait être corrélée avec la perte des propriétés mécaniques des membranes permettant de faire le lien entre l évolution de la structure chimique et la perte des propriétés macroscopiques. Il apparait donc au final que l additif ajouté au PES pour rendre les membranes hydrophiles est le talon d Achille de la structure. Le suivi de l oxydation de la PVP contenue dans les membranes exposées à NaOCl a été proposé pour servir de marqueur moléculaire de vieillissement.This work was devoted to the study of the impact that chemical cleaning with sodium hypochlorite (NaOCl) has on polyethersulfone (PES)/polyvinylpyrrolidone (PVP) (95%/5%) membranes, commonly used for water and milk filtration processes. In onsite plants, chemical cleanings are widely used to maintain membranes filtration properties. The aim of this thesis is to determine the degradation mechanisms of these two polymers in contact with NaOCl and to correlate this information with the evolution of the macroscopic properties of the membrane through a multi scale analysis. Firstly, the study of NaOCl impact on both PVP and PES, treated separately as model polymers , showed us that dissolved PVP is oxidised, whereas PES film remains stable. Thanks to the identification of PVP oxidation products, a radical degradation mechanism by means of hydroxyl radicals from NaOCl solution has been proposed. Secondly, in order to overcome membrane heterogeneities, several films with different PES/PVP ratios were prepared by varying the amount of PVP. The immersion of these films in NaOCl solutions provoked the oxidation of both PVP and PES, allowing us to clearly identify the degrading effect that PVP has in PES oxidation. Thirdly, the evolution of PVP chemical structure was correlated with the loss of the membrane mechanical properties, demonstrating that PVP, used as an additive (5%), is the weak point of PES/PVP membranes. The monitoring of PVP oxidation in membranes in contact with NaOCl was proposed as a molecular marker of ageing.CLERMONT FD-Bib.électronique (631139902) / SudocSudocFranceF

Why does poly(acrylic acid) addition improve the quality of holograms recorded in dichromated poly(vinyl alcohol)?

International audienceHolographic measurements have shown that the addition of 0.5% of poly(acrylic acid) (PAA) can improve the quality of holograms recorded in poly(vinyl alcohol) (PVA) doped with ammonium dichromate (ADC). The purpose of this paper is to explain this improvement. First, an analytical approach investigated the structural and architectural modification of the polymeric matrix and the fate of the various chromium species within PVA/PAA/ADC films. The addition of PAA in dichromated PVA led to a pre-reticulation of the polymeric matrix. This process increased with the amount of PAA. Second, an analytical approach focused on the evolution of PVA/PAA/ADC films upon irradiation at 365 nm, which is representative of hologram formation. The improvement brought by the presence of 0.5% of PAA in PVA/ADC was assigned to an additional source of crosslinking through the formation of covalent bonds. This process paralleled the crosslinking through coordination bonds involving Cr(V) and PVA units. At 0.5% of PAA, the mobility of the medium before exposure was sufficient to allow the migration of the species involved in the reticulation process during hologram formation, whereas higher concentrations of PAA inhibited this migration