The synthesis of crosslinked copolymers of maleilated chitosan and acrylamide

By acylating chitosan with maleic anhydride in formamide medium trisubstituted products (on one amine and two hydroxyl groups of the saccharide unit) have been obtained, as has been confirmed by IR spectroscopy, titration carboxylic groups, and determination of the content of olefin bonds. By copolymerizing trisubstituted maleilated chitosan and acrylamide in water solution crosslinked polymers have been obtained. Their swelling in water decreases with an increase in the share of maleilated chitosan in the initial mixture of reagents and with a decrease in dilution of the initial mixture of reaction components. Consumption of maleilated chitosan double bonds in this case varies from 40 to 70%.     

Modeling molecular weight distribution of comb-branched graft copolymers

Grafting one type polymer onto a different polymer type may yield a comb-branched copolymer. The branching density has a significant effect on its overall molecular weight distribution. A general model is derived to describe the bivariate distribution of molecular weight and branching density for such comb copolymers. The model is applicable for various grafting mechanisms provided the side chains are randomly grafted onto the backbone. The determining parameters are the molecular weight distributions of backbone and side chains, and the branching density. Analytical expressions are obtained for the cases of the side chains having uniform and Schulz–Zimm distributions. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 705–714, 1998     

Effect of synthesis conditions on molecular characteristics of acrylamide copolymers with acrylic acid,carriers of cationic biologically active substances

Methods of molecular hydrodynamics and optics were used to study properties of aqueous solutions of acrylamide copolymers with acrylic acid. Dependences of the molecular characteristics of the copolymers on their synthesis conditions were determined and conditions were found in which the process of radical copolymerization of acrylamide with acrylic acid yields water-soluble carboxyl-containing acrylamide copolymers with molecular masses not exceeding 4×10⁴ Da.     

Effect of molecular architecture on phase behavior of graft copolymers

Influence of molecular architecture on phase behavior of graft copolymer melts was studied by using a reciprocal-space self-consistent filed theory (SCFT). The phase diagrams were examined as functions of the architectural parameters describing the graft copolymers (i.e., the number of grafts and the position of first junction). In comparison with the well-known phase diagram of diblock copolymers, the phase diagrams of the graft copolymers are asymmetric. When the number of grafts or the position of first junction varies, the boundaries of order-order transitions have shifts due to the variation in the chain stretching energy. The change in molecular architecture also significantly alters the domain spacing of ordered structures but has weak impact on the density distributions of graft copolymers. For comparison of the theoretical predictions with the existing experimental results, the phase diagrams of graft copolymers were also calculated at strong segregation. The SCFT calculations can accurately capture the characteristics of the phase behavior of graft copolymer melts.     

Complexation of chitosan with maleic acid copolymers

The complexation of chitosan with alternating copolymers of maleic acid with N-vinylpyrrolidone, ethylene, or styrene is studied. It is found that the process is of a cooperative character and that the binding constants and the Hill parameters are dependent on the nature of a nonionogenic comonomer maleic acid in the synthetic polyanion and on the conditions of complexation. The data of atomic force microscopy and turbidimetric titration confirm the effect of temperature on the conformation of interacting macromolecules and the size of macromolecular aggregates. It is shown that the composition and yield of insoluble interpolyelectrolyte complexes at constant pH are determined by the reactant ratio, the temperature, and the initial concentration of polyelectrolytes.     

Cationic temperature-responsive poly(N-isopropyl acrylamide) graft copolymers: from triggered association to gelation

In this work temperature-triggered association and gel formation within aqueous solutions of a new family of cationic poly( N-isopropyl acrylamide) (PNIPAm) graft copolymers have been investigated. Five copolymers were synthesized using aqueous atom transfer radical polymerization (ATRP) involving a macroinitiator based on quaternarized N, N-dimethylaminoethyl methacrylate units (DMA+). The PDMA+) x - g-(PNIPAmn)y copolymers have x and y values that originate from the macroinitiator; values for n correspond to the PNIPAm arm length. The copolymer solutions exhibited temperature-triggered formation of nanometer-sized aggregates at the cloud point temperature, which was 33-34 degrees C. The aggregates were investigated using variable-temperature turbidity, hydrodynamic diameter, and electrophoretic mobility measurements. The aggregates were clearly evident using SEM and flowerlike or spherical morphologies were observed. Variable-temperature electrophoretic mobility measurements revealed that the zeta potentials of the aggregates increased with DMA+ content. A study of the effect of added NaNO3 showed that electrostatic interactions controlled the size of the aggregates. The concentrated graft copolymer solutions showed temperature-triggered gelation when the copolymer concentrations exceeded 5 wt %, Fluid-to-gel phase diagrams were constructed. It was found that electrostatic interactions also controlled the gelation temperature. A correlation was found between aggregate size and the minimum copolymer concentration needed to form a gel. A mechanism for the temperature-triggered structural changes leading to the formation of aggregates (in dilute solution) or gels (in concentrated solutions) is proposed.     

Synthesis and hydrodynamic and molecular characteristics of N-methacryloylglucosamine N-vinylformamide copolymers

Random 50: 50 N-methacryloylglucosamine-N-vinylformamide copolymers were synthesized, and their hydrodynamic and molecular characteristics were examined. For the copolymers with the molecular weight 70 < M × 10⁻³ g mol⁻¹ < 570 in 0.2 M NaCl, the Kuhn-Mark-Houwink-Sakurada equations were obtained, which relate the intrinsic viscosity and the translational diffusion and centrifugal sedimentation coefficients, on the one hand, to the molecular weight, on the other. The length of the statistical segment of the copolymer chains was estimated. Original Russian Text G.M. Pavlov, E.V. Korneeva, N.P. Ivanova, O.A. Pavlova, E.F. Panarin, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 5, pp. 798–803.     

Induced degradation of chitosan,conjugated with block copolymerization with acrylamide

Synthesis of block copolymers of chitosan with acrylamide, involving formation of acrylamide blocks on glucosamine blocks generated by induced degradation of chitosan macromolecules by the hydrogen peroxide-ascorbic acid system, was studied.     

Flocculation activity of anionic copolymers of acrylamide with respect to titanium dioxide suspension as influenced by their molecular properties

The kinetics of sedimentation of titanium dioxide suspension in the presence of ionic (anionic) acrylamide copolymers in the mode of free (unrestricted) sedimentation was studied. The effect of concentration and molecular properties of the copolymers on their flocculation activity was evaluated by sedimentation analysis.     

Synthesis of graft copolymers with polyisobutylene branch chains

<正>The copolymerization of 4-vinylbenzyl chloride(VBC) and vinyl acetate(VAC) was carried out in toluene at 75℃via radical polymerization using 2,2'-azo-bis-(isobutyronitrile)(AIBN) as an initiator.The random copolymers of poly(4-vinylbenzyl chloride-co-vinyl acetate)(P(VBC-co-VAC)) with number average molecular weight(M_n) from 2000 to 6900,relatively narrow molecular weight distribution(MWD,M_w/M_n ca.2.0) and with different copolymer composition of 4-vinylbenzyl chloride(VBC) from 17 mol%to 62 mol%could be obtained.The P(VBC-co-VAC) copolymers with an average number of 7 to 13 initiating sites of benzyl chloride per macromolecule could be used for the cationic polymerization of isobutylene(IB).The cationic polymerizations of IB were further conducted by using P(VBC-co-VAC) copolymers as macroinitiators in conjunction with TiCl_4 at -40℃in CH_2Cl_2.The effects of VBC/TiCl_4(molar ratio) on monomer conversion,M_n and MWD of the resultant copolymers were investigated under 3 sets of conditions.It is found that P(VBC-co-VAC)-g-PIB copolymers with relatively narrow MWD(M_w/M_n ca.2.0) and with terminal tert-chlorine functional groups in branched PIB chains could be successfully synthesized when VBC/TiCl_4(molar ratio) was set in the range from 0.10 to 1.12.The unimodal GPC curve of the P(VBC-co-VAC)-g-PIB copolymers by RI detector was almost in harmony with the GPC curve by UV detector.The TEM image of the P(VBC-co-VAC)-g-PIB copolymer stained by RuO indicated that the copolymer formed a two-phase morphology with P(VBC-co-VAC)-rich domains of 20-100 nm in size tethered by PIB branch segments.     

In-situ preparation of graft copolymers

Graft copolymers are closer to supermolecular structures than any other class of polymers. Most grafting reactions proceed in demixed blends or lead in situ to such blends The competition of chemical chain coupling and physical phase separation generates complex phase morphologies that cannot (or not so directly) be produced otherwise. To demonstrate potential and problems of graft copolymer systems, high-impact thermoplastics, block-graft copolymers and reactive blending are discussed.     

Chromatography of amphiphilic graft copolymers

Amphiphilic comb polymers were prepared through grafting poly(ethylene glycol) methyl ether (MPEG 2000) onto acrylic and methacrylic copolymers. The graft copolymers were purified from unreacted MPEG by partition chromatography on methanol pretreated fibrous cellulose using ethyl acetate and methanol as eluents. The separation was found to depend on the water contents of the cellulose and the eluents. It is proposed that one parameter of importance for the chromatographic separation is the formation of hydrated inverted micelles. The amphiphilic comb polymers were shown by gel chromatography on Sepharose to form high molecular weight aggregates in water. On addition of sodium lauryl sulphate or inorganic salts to the eluent at low ionic strengths these aggregates dissociated and were fractionated by the gel. It was also shown that on GPC in THF solution on Styragel columns the polymers exhibited apparent molecular weights equal or smaller than those of the corresponding backbones. This effect may be a consequence of the graft copolymers having relatively small hydrodynamic volumes, and this idea is supported by the fact that their intrinsic viscosities generally were lower than those of the backbones. However, adsorption on the Styragel columns also may be of importance.     

Synthesis of conducting block and graft copolymers with polyether segments

Synthesis of block and graft copolymers containing polyether and conducting polypyrrole sequences were described. Pyrrole moieties were incorporated at the chain ends of polytetrahydrofuran and polysiloxane and at the side chains of polyethyl vinylether by ionic polymerization and appropriate chemical reactions. Subsequent electropolymerization with pyrrole through these moities yielded free standing films of the corresponding block and graft copolymers. The formation copolymers was evidenced by FTIR spectroscopy and extraction with solvent of the precursor homopolymers. The thermal and morphological properties were also characterized. The two surface of the copolymer films generally differ in appearance, the surface at the solution side being cauliflowerlike or wrinkled, whereas the surface at the electrode side smooth. Conductivies of the copolymers were comparable with that of the pure polypyrrole.     

Block and graft copolymers of 2-oxazolines

The cationic ring-opening polymerization of 2-oxazolines is known to be initiated by alkyl halides, Lewis acids and esters of strong acids. The polymerization proceeds by a living mechanism. Numerous block and graft copolymers have already been described. Recently it was found that chloroformates (R-O-CO-CI) are also useful initiators. The mechanism of the initiation and propagation is discussed. This type of initiators allows the synthesis of different novel two-block and three-block copolymers, star-shape polymers, and a graft copolymer with a polyvinylacetate backbone.     

Morphologies and bridging properties of graft copolymers

Morphologies and bridging properties of graft copolymers in the bulk state were studied by using a real-space algorithm of self-consistent field theory in two dimensions. The phase transition from cylindrical to lamellar phase can be triggered by changing the position of graft points and the number of branches. The fraction of bridged conformation, f(bridge), shows a tendency to decrease with increasing the length of free end blocks, tau1, and the number of branches, m. The value of f(bridge) has a discontinuous drop when the transition from cylindrical to lamellar phase takes place. The relationship between m and the number of bridged chains per unit area, nb, which is associated with the mechanical properties of copolymers, was also examined. It was found that nb increases with increasing m in the cylindrical phase. However, in the lamellar phase, nb decreases when m increases. It is proposed that the position of graft points and the number of branches are two important parameters for material design.     

Hydrodynamic properties of model 3-miktoarm star copolymers

The synthesis of well-defined, nearly monodispersed, 3-miktoarm (from the greek word μlkτós meaning mixed) star copolymer of the A₂B type is described. A and B is either polystyrene (PS), polybutadiene (PBd), or polyisoprene (PI). The sequential controlled addition of living anionic B and A chains to methyltrichlorosilane leads to narrow molecular weight distribution miktoarm star copolymers with homogeneous composition. Characterization was carried out by size exclusion chromatography, low-angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, nuclear magnetic resonance and ultraviolet spectroscopy. Analysis of [η], R_H and R_v of the A₂B and one A₂B₂ miktoarm copolymers, suggests that a small expansion of the copolymer occurs either in a good solvent for both species or in a Θ solvent for one of them, as compared with the corresponding star homopolymers. This is in contrast to results obtained on linear block copolymers, and is due to the increased occurrence of heterocontacts in the miktoarm starshaped architecture. © 1995 John Wiley & Sons, Inc.     

Conducting graft copolymers of pyrrole and thiophene with random copolymers of methyl methacrylate and 3-methylthienyl methacrylate

Random copolymers of 3-methyl thienylmethacrylate and methyl methacrylate were synthesized via free radical polymerization. Electro-copolymerizations of random copolymers with thiophene and/or pyrrole were carried out in acetonitrile-tetrabutylammonium tetrafluoroborate (TBAFB), water-p-toluene sulfonic acid (PTSA) solvent-electrolyte couples. Oxidative polymerization of thiophene functionalized random copolymer was also achieved by constant current electrolysis and chemical polymerization. The characterizations were done by conductivity measurements, cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermal gravimetry analysis (TGA), scanning electron microscopy (SEM).