Solution properties of dextran–polyacrylamide graft copolymers (original) (raw)
Related papers
Anomalous behaviour of comb-like dextran–polyacrylamide copolymers in mixed solvents
European Polymer Journal, 2009
Copolymers obtained by grafting polyacrylamide (PAA) onto dextran (DEX) have been synthesised by ceric-ion-reduced redox initiation method. These copolymers have been characterized by light scattering and self-exclusion chromatography. Viscometry measurements in mixed solvents, water/dimethyl formamide (DMF) have revealed an anomalous behaviour reminiscent of a polyelectrolyte behaviour, namely a strong upturn when decreasing polymer concentration, effect which is absent in pure water. The origin of this phenomenon has been studied by determining by means of SAXS the short-range molecular structure of these copolymers in the binary solvents. Comparison has been also performed with water/methyl formamide (MF) and water/formamide (FA) binary solvents where the pseudo-polyelectrolyte effect is absent. A molecular model is discussed on the basis of the results from SAXS that throws some light on the viscometry effect. This model considers the occurrence of an interdigitation process between the PAA grafts together with the formation of a PAA-DMF complex.
Star-Like Dextran-graft-(polyacrylamide-co-polyacrylic acid) Copolymers
Macromolecular Symposia, 2014
Star-like dextran-graft-(polyacrylamide-co-polyacrylic acid) (D-g-(PAAco-PAAc) copolymers in a salt form were obtained by alkaline hydrolysis of Dextrangraft-Polyacrylamide (D-g-PAA) samples. The internal structure of D-g-PAA in solution predetermined the reaction course and the conversion degree depended upon the initial architecture of macromolecules. It was shown that macromolecules of D-g-(PAA-co-PAAc) acquired extended conformation because grafted chains became greatly straightened when charged functional groups appeared. No polyelectrolyte effect for synthesized D-g-(PAA-co-PAAc) samples was registered. Star-like polyelectrolytes were proved to be more efficient matrices in comparison with linear anionic Polyacrylamide for silver nanoparticle in situ synthesis.
Branched Dextran-graft -Polyacrylamide Copolymers as Perspective Materials for Nanotechnology
Macromolecular Symposia, 2012
Branched dextran-graft-polyacrylamide copolymers (D-g-PAAn) with different number of PAA-grafts have been synthesized for further conversion them to polyelectrolytes dextran-graft-(polyacrylamide-co-polyacrylic acid). It is shown that D-g-PAAn internal structure in water solution is more compact in comparison with linear polyacrylamide and depends upon the distance between PAA grafts. The branched polyelectrolytes are obtained by alkaline hydrolysis of synthesized D-g-PAAn samples. The conversion of nonionic polymers to partial anionic form depends upon the macromolecular internal structure of D-g-PAAn. The degree of transformation of amide groups to carboxylate ones is higher for branched copolymers than for linear PAA at the same condition. The synthesized branched copolymers are shown to be perspective as flocculation agents and the matrices for synthesis of the stable Ag nanosystems.
Light Scattering and Viscosimetry Study of Star-Like Dextran-Graft-Polyacrylamide
Chemistry & Chemical Technology, 2009
Dextran-graft-Polyacrylamide copolymers (D-g-PAA) with a polysaccharide backbone having different molecular weights (Mw = 20 000 and Mw = 70 000) and with various number of PAA-grafts per one Dextran macromolecule have been synthesized. Light scattering and viscometry investigations have shown that the internal structure of D-g-PAA copolymers depends upon the distance between PAA-grafts. Compactness of D20-g-PAA copolymers is lower in comparison with D70-g-PAA samples due to different conformations of PAA grafted chains: a “mushroom” conformation for D70-g-PAA and a “worm-like” one for D20-g-PAA samples.
Express Polymer Letters
Dextrin/starch-graft-poly(butyl acrylate-co-styrene) copolymers have been synthesized by radical graft copolymerization and their structure and mechanical properties are reported. High molecular weight grafted chains formation is favored, leading to a low degree of substitution of starch hydroxyl groups. Wide-Angle-X-ray Scattering (WAXS) analysis indicates that all materials are amorphous and Transmission Electron Microscopy (TEM) investigations reveal a two-phase morphology. This is further confirmed by the presence of two glass transitions, one related to the starch/dextrin macromolecules and sensitive to water content, and one assigned to the grafted polymers that is composition dependent. Water uptake is controlled by dextrin/starch content but diffusivity increases with the butyl acrylate ratio. The mechanical behavior is dependent on monomer ratio, and water content. Increasing butyl acrylate ratio improves the ductility of the sample while materials become brittle as soon as styrene ratio is predominant in the grafted chains. While no effect of molecular weight of starch substrate on structure and thermal behavior is evidenced, dextrin-based materials are slightly more ductile than starchbased ones. The interest of using dextrin instead of starch is further highlighted by a lower viscosity of the reactive medium, together with an improved processability, as structural materials can be obtained over a wider range of composition than with native starch.
European Polymer Journal, 2009
Thermosensitive anionic block copolymers of sodium 2-acrylamido-2methylpropanesulfonate (AMPS) and N-isopropylacrylamide (NIPAAM) with different block lengths were prepared by atom transfer radical polymerization (ATRP). Controlled polymerization was achieved by using ethyl 2-chloropropionate (ECP) as initiator and CuCl/CuCl 2 /tris(2-dimethylaminoethyl)amine (Me 6 TREN) catalytic system in DMF:water 50:50 (v/v) mixtures at 20 8C. Blocks lengths ranging from 36 to 98 repeating units were obtained. The association properties in aqueous solutions at different NaCl ionic strengths were studied as a function of temperature and polymer concentration by dynamic light scattering, fluorescence spectroscopy, and energyfiltered transmission electron microscopy. The block copolymers with a higher pNI-PAAM/pAMPS ratio formed spherical core-shell type micelles independently of the ionic strength. The block copolymers with lower pNIPAAM/pAMPS ratio formed coreshell type micelles at high ionic strength. Larger particles were observed at low ionic strength, which could be due to the formation of vesicles or compound micelles/micellar clusters. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4830-4842, 2008
Macromolecules, 2006
Characteristics of polymer forming poly(isobutylcyanoacrylate) (PIBCA) nanoparticles used as drug delivery systems were investigated. The nanoparticles were prepared by emulsion polymerization of IBCA in the presence of dextran by either anionic or redox radical emulsion polymerization. These methods allowed complete polymerization of IBCA. The nanoparticles were formed by heterogeneous polymers. Characterization of PIBCA and dextran parts after selective hydrolysis of the counterpart highlighted differences in term of composition and structure of polymer. The anionic emulsion polymerization (AEP) led to the simultaneous formation of homopolymer of PIBCA and of copolymers of several short PIBCA chains grafted on a dextran chain. In redox radical emulsion polymerization (RREP), nanoparticles contained only copolymers with bloc structure in which PIBCA chains exhibited a high molecular weight and a broad distribution. These results confirmed hypothesis on formation of diblock copolymers by RREP and of grafted copolymers by AEP.
Controlled synthesis of amphiphilic biodegradable polylactide-grafted dextran copolymers
Journal of Polymer Science Part A: Polymer Chemistry, 2004
The whole controlled synthesis of novel amphiphilic polylactide (PLA)grafted dextran copolymers was achieved. The control of the architecture of such biodegradable and potentially biocompatible copolymers has required a three-step synthesis based on the "grafting from" concept. The first step consisted of the partial silylation of the dextran hydroxyl groups. This protection step was followed by the ring-opening polymerization of D,L-lactide initiated from the remaining OH functions of the partially silylated polysaccharide. The third step involved the silylether group deprotection under very mild conditions. Based on previous studies, in which the control of the first step was achieved, this study is focused on the last two steps. Experimental conditions were investigated to ensure a controlled polymerization of D,L-lactide, in terms of grafting efficiency, graft length, and transesterification limitation. After polymerization, the final step was studied in order to avoid degradation of both polysaccharide backbone and polyester grafts. The chemical stability of dextran backbone was checked throughout each step of the synthesis. PLA-grafted dextrans and PLA-grafted (silylated dextrans) were proved to adopt a core-shell conformation in various solvents. Furthermore, preliminary experiments on the potential use of these amphiphilic grafted copolymers as liquid/liquid interface stabilizers were performed.
Polymer, 2005
Potassium diperiodatocuprate-initiated graft polymerization was found to be an efficient and convenient method for grafting of acrylic acid (AAc) onto superporous polyacrylamide gels, so called cryogels (pAAm cryogels). It was possible to achieve grafting degrees as high as 70% with about 25% yield of grafted polymer with respect to the initial amount of monomer. The superporous structure of the cryogels promoted grafting by providing an ample surface of the gel for grafting, ensuring good mass transfer inside the gel sample and allowing to wash easily both homopolymer of AAc and insoluble by-products formed during the polymerization reaction. The grafted cryogels could be dried at 60 8C and re-swollen with retaining their properties. The adsorption of water vapours by dried pAAm cryogels was marginally dependent on the degree of grafting. The swelling of AAc-grafted pAAm cryogel increased pronouncedly with increasing pH. The adsorption of lowmolecular weight ligand, Cu(II), by AAc-grafted pAAm cryogels increased linearly with the degree of grafting, while binding of highmolecular weight ligand, lysozyme, increased linearly till the degree of grafting of about 40% followed by a sharp, nearly three-fold increase in lysozyme binding when the degree of grafting increased from 60 to 70%. The results indicate that a 'tentacle'-type binding of lysozyme to grafted polyAAc takes place after a certain degree of grafting has been reached. q Polymer 46 9596-9603 www.elsevier.com/locate/polymer 0032-3861/$ -see front matter q
Molecular Crystals and Liquid Crystals, 2005
The influence of poly(vinyl alcohol) matrix on stereoregularity of replica polyacrylamide chains in matrix radical graft copolymerization process when varying the grafts number and molecular weight is studied by high-resolution NMR spectroscopy. It was ascertained that the microstructure of formed polymer at homopolymerization and matrix copolymerization processes are not differed. 1 H NMR spectroscopy suggests a few contacts of graft chains with the main chain through H-bonding in intramolecular polymer-polymer complex forming in macromolecules of investigated poly(vinyl alcohol)-to-polyacrylamide graft copolymer.