77 research outputs found
An Orthogonal Modular Approach to Macromonomers Using Clickable Cyclobutenyl Derivatives and RAFT Polymerization
A series of cyclobutene-based macromonomers
derived from monomethyl ether poly(ethylene oxide) (PEO),
poly(ethyl acrylate) (PEA), poly(N-isopropylacrylamide)
(PNIPAM), and PEO-b-PNIPAM were synthesized by
âclickâ copper-catalyzed azideâalkyne cycloaddition
(CuAAC) and reversible additionâfragmentation chain transfer
(RAFT) polymerization. First, original di- and trifunctional
cyclobutene precursors with azido, alkyne and/or chain
transfer agent were successfully obtained and fully characterized.
Azido- and alkyne-functionalized cyclobutenes were then conjugated with modified PEO bearing azido or alkyne groups,
resulting in cyclobutene-based PEOs in quantitative conversions as ascertained by NMR spectroscopy and MALDIâTOF mass
spectrometry. The new chain transfer agent-terminated cyclobutene was used to mediate the RAFT polymerization of ethyl
acrylate and N-isopropylacrylamide. Well-defined polymers with controlled molecular weights (Mn = 3700â11 500 g·molâ1) and
narrow molecular weight distributions (PDI = 1.06â1.14) were thus obtained that retain the cyclobutene functionality,
demonstrating the orthogonality of the RAFT process toward the cyclobutenyl insaturation. Combination of CuACC and RAFT
polymerization was used to afford PEO-b-PNIPAM block copolymer functionalized by a cyclobutene end-group
Cyclobutenyl macromonomers: Synthetic strategies and ring-opening metathesis polymerization
AbstractIn contrast to their (oxa)norbornenyl counterparts, cyclobutenyl derivatives have remained relatively unexplored in ring-opening metathesis polymerization (ROMP), despite ROMP of cyclobutene derivatives yields unsaturated polymers based on a strictly 1,4-polybutadiene backbone that is not easily attainable by other routes. This article summarizes work done in our group in the field of cyclobutenyl-capped macromonomers that are convenient building blocks for the synthesis of graft (bottle-brush) copolymers by ROMP via the so-called macromonomer (or grafting-through) route. Synthetic strategies employing orthogonal chemistries such as reversible deactivation radical polymerization techniques (atom transfer radical polymerization â ATRP, and reversible addition-fragmentation chain transfert (RAFT) polymerization) and recent developments using copper-catalyzed azideâalkyne cycloaddition click chemistry are highlighted. Furthermore, ROMP of the so-obtained macromonomers, including preliminary novel results regarding ROMP of cyclobutenyl-capped macromonomers prepared through RAFT polymerization and click chemistry are reported and discussed
LâAubance et le Layon, Ă©volutions paysagĂšres de deux vallĂ©es en contexte viticole
Cet ouvrage propose une analyse approfondie de la controverse environnementale portant sur le dĂ©mantĂšlement des seuils et barrages en vue de restaurer la qualitĂ© de lâeau et des milieux aquatiques. Le sujet est traitĂ© sous lâangle des sciences humaines et sociales et plus prĂ©cisĂ©ment celui de la gĂ©ographie environnemental
Novel hydrogel obtained by chitosan and dextrin-VA co-polymerization
A novel hydrogel was obtained by reticulation of chitosan with dextrin enzymatically linked to vinyl acrylate (dextrin-VA), without cross-linking agents. The hydrogel had a solid-like behaviour with GâČ (storage modulus) >> Gâł (loss modulus). Glucose diffusion coefficients of 3.9 Ă 10â6 ± 1.3 Ă 10â6 cm2/s and 2.9 Ă 10â6 ± 0.5 Ă 10â6 cm2/s were obtained for different substitution degrees of the dextrin-VA (20% and 70% respectively). SEM observation revealed a porous structure, with pores ranging from 50 ”m to 150 ”m
Synthesis and characterization of polymers for nonlinear optical applications
International audienceA difunctional NLO Azo-Dye chromophore has been synthesized and polymerization has been performed with a comonomer bearing a side-chain epoxy group. Deposition of the polymer on glass substrates was performed by spin-coating, resulting in uniform films up to 2 ”m thickness. The orientation of the chromophore was performed under a " pin-to-plane " positive corona discharge followed by a heat-treatment in order to obtain reticulation of the films. Molecular orientation has been investigated using UV-Vis. and Raman spectroscopy. Poling of the films results in a decay of absorbency as well as in a blue shift of the spectrum. At the same time, the 1600 cm-1 band disappears from the Raman spectra, indicating orientation of the chromophores. Cross-linking has been studied by FTIR and all-optical poling and showed an improved stability of the electro-optic thin films
Interplay between Structure and Dynamics in Chitosan Films Investigated with Solid-State NMR, Dynamic Mechanical Analysis, and X-ray Diffraction
Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Clâ») was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Clâ» counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content
Chitosan Hydrogels Incorporating Colloids For Sustained Drug Delivery
International audienceIn today's biomedical research, a huge effort is being made towards the development of efficient drug delivery systems, achieving sustainable and controlled delivery of drugs. Chitosan (CS) hydrogels are high water content materials with very relevant biological properties to that purpose. Their use for a local and delayed delivery has already been demonstrated for a wide variety of therapeutic agents. One relatively recent strategy to improve these CS-based systems consists in the insertion of colloids, embedding drugs, within their three-dimensional matrix. This provides a second barrier to the diffusion of drugs through the system, and allows to better control their release. The main objective of this review is to report the many existing complex systems composed of CS hydrogels embedding different types of colloids used as drug delivery devices to delay the release of drugs. The various biomedical applications of such final systems are also detailed in this review
Cell elongation is an adaptative response for clearing long chromatid arms from the cleavage plane.
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