Competing reactions in anionic gel-poly(propylene imine) dendrimer-surfactant ternary systems

Competitive interactions in ternary systems including a lightly crosslinked polyanionic hydrogel, a protonated Astramol? poly(propylene imine) dendrimer (of first to fifth generation), and an ionic surfactant were studied. It was found that the direction of the substitution reactions in systems containing cationic surfactants depends on the length of the aliphatic radical in the surfactant molecule as well as on the dendrimer generation number. Depending on these parameters, the interpolyelectrolyte complex formed by the network polyanion and the cationic dendrimer is either capable or incapable of sorbing surfactant cations from aqueous solutions, thereby transforming into the network polyanion-cationic surfactant complex with the release of dendrimers to the surrounding solution. It was shown that the substitution reaction in systems containing anionic surfactants leads to the formation of a polyanionic gel reinforced by particles of the dendrimer-anionic surfactant complex.     

The effect of the charge of astramol™ poly(propylene imine) dendrimers on interaction with polyanionic gels

The effect of the charge of Astramol^? poly(propylene imine) dendrimers of the third and fourth generations on activated sorption of dendrimer molecules by weakly crosslinked polyanionic networks was studied. It was shown that the formed interpolyelectrolyte complex was markedly enriched in the weakly charged dendrimer as the degree of dendrimer neutralization decreased. As was found, depending on the conditions of sorption of dendrimers by oppositely charged networks, this process leads to the formation of either macroscopically heterogeneous “shell-core” structures or microheterogeneous composites with uniform distribution of micrometer-sized clusters of dendrimer molecules in the gel matrix. The structure of such systems separated at the microphase level was studied by the laser scattering technique. Their high ordering was established, and the reasons behind the formation of various alternative heterophase systems were discussed.     

增塑化学微交联聚氯乙烯中化学交联和物理交联的协同作用

由氯乙烯／ 邻苯二甲酸二烯丙基酯（ＶＣ／ＤＡＰ） 悬浮共聚合成了化学微交联聚氯乙烯（ＰＶＣ） 树脂,并进行增塑加工．共聚得到的化学交联ＰＶＣ 具有溶胶／ 凝胶分配特性,交联密度较低;化学交联ＰＶＣ 的溶胶和凝胶均存在分子链缠结作用,尤其当凝胶含量较高时,物理缠结对凝胶交联密度有较大贡献．化学交联对增塑ＰＶＣ 结晶性的影响较小,因此在增塑化学微交联ＰＶＣ 中同时存在化学交联网络和以分子链物理缠结点和微晶为交联点的物理交联网络,两者协同影响增塑ＰＶＣ 材料的性能．     

Sorption of anionic amphiphilic block copolymers by a network polycation

The interaction of amphiphilic block copolymers comprising an anionic block (polyacrylate or polymethacrylate) and a hydrophobic block (polystyrene, poly(butyl acrylate) or polyisobutylene) with lightly crosslinked poly(N,N-diallyl-N,N-dimethylammonium chloride) is studied for the first time. It is shown that the cationic hydrogel can sorb anionic amphiphilic block copolymers via electrostatic interaction with the corona of block copolymer micelles. The rate of sorption of block copolymer polyelectrolytes is significantly lower than the rate of sorption of linear polyions and is controlled by the lengths of the hydrophilic and hydrophobic blocks and the flexibility of the latter blocks. The sorption of amphiphilic block copolymers is accompanied by their self-assembly in the polycomplex gel and formation of a continuous hydrophobic layer impermeable to water and the low-molecular-mass salt dissolved in it.     

Interaction of ampholyte dendrimers with network polycations and polyanions

The interaction of polyampholyte propylenimine dendrimers of five generations containing peripheral carboxyl and inner tertiary amino groups with lightly crosslinked highly swelling polyelectrolyte gels has been studied. It has been shown that the polyampholyte dendrimers of all five generations are efficiently sorbed by a polyanion sulfur-containing hydrogel (below the isoelectric point) and a polyamine hydrogel (above the isoelectric point) to give rise to interpolyelectrolyte complexes. The composition of interpolyelectrolyte complexes and the equilibrium concentration of the dendrimer in the surrounding solution are appreciably affected by the pH of the medium. Amount of zwitterion pairs in a dendrimer molecule significantly influence the formation of interpolymer salt bonds. The polyampholyte dendrimer can pass from an anionic hydrogel to a cationic one upon a small change in pH near the isoelectric point.     

Rheological analysis as a means for determining the silane crosslink network structure and content in crosslinked polymer composites

For evaluating the crosslink content of a polymer, gel content determination is a commonly used method. However, for crosslinked polymer composites containing particulate filler, the gel content may be overestimated due to partly trapping filler inside the gel portion. In this paper, parallel-plate rheology was used, together with the gel determination and FTIR measurement, for determining the silane crosslink network structure and content in crosslinked ethylene–octene copolymer composites. The effects of filler surface property on structure and content of silane crosslink are also discussed. The results show that a correlation plot between gel content, IR absorption index and crosslink density provides useful information on changes in silane network structure and properties of the crosslinked composites. The network structure formed (loose or tight network) shows a strong influence on the final tensile properties of the crosslinked products.     

Self-assembly of ionogenic surfactants during their interaction with poly(propylenimine) dendrimers

The structure of complexes formed by poly(propylenimine) dendrimers of five generations and anionic micelle-forming surfactants is studied by X-ray diffraction. It is shown that, in complexes of lower generation dendrimers, the lamellar packing of surfactants is dominant. In complexes formed by dendrimers of the fourth and fifth generations, packing typical of compact dendrimer molecules prevails. This packing can be attributed to the distorted dense packing of ball-like complex species. Structural models of complexes that allow for penetration of surfactants into the dendrimer molecule and the size ratio of the aliphatic radical of a surfactant and a dendrimer are advanced.     

Measurement of concentration gradients in swelling crosslinked polymer beads

The concentration of solvent in the gel phase of a swelling polystyrene–divinylbenzene copolymer bead has been measured as a function of the radius by optical interference techniques. It is found that an appreciable gradient exists even shortly after the core disappears. Results are presented for two cases: a very lightly crosslinked bead that exhibits negligible birefringence while swelling, and a more tightly crosslinked network in which the birefringence must be considered. It is also found that the refractive index of the unswollen bead is considerably less than that found by extrapolation from the swollen state; this effect is reasonable when the “free volume” in the bulk polymer is considered.     

SAXS study on complexes formed by anionic poly(sodium methacrylate‐co‐N‐isopropylacrylamide) gels with cationic surfactants

Small‐angle X‐ray scattering (SAXS) has been used to study the nanostructures of complexes formed by slightly crosslinked anionic copolymer gels of poly(sodium methacrylate‐co‐N‐isopropylacrylamide) [P(MAA/NIPAM)] interacting with cetylpyridinium bromide (CPB), and alkyltrimethylammonium bromide (C_nTAB, 10 ≤n ≤ 18), respectively. Both the charge density of polyelectrolyte gels and the surfactant alkyl tail length could induce the phase structure transition from Pm3n space group cubic to hexagonal close packing of spheres (HCP), while the different polar groups of pyridinium and trimethylammonium with the same hydrophobic cetyl chain in surfactants had no significant effects on the structures of complexes formed with the same gels. The highly ordered structures were shown to be formed by the self‐assembly of ionic surfactants inside the anionic gel network, driven by both electrostatic and hydrophobic interactions. Freeze drying the water‐equilibrated complexes could collapse the formed ordered structures. However, the highly ordered structures could be restored after the dried complexes were reswollen by water under the same conditions, indicating that the highly ordered water‐equilibrated complexes were thermodynamically stable. Copyright © 2000 John Wiley & Sons, Ltd.     

Polyurethane/polystyrene one-shot interpenetrating polymer networks with good damping ability: Transition broadening through crosslinking,internetwork grafting and compatibilization

Good damping materials should exhibit a high loss factor value over a broad temperature range. Polyurethane and polystyrene are highly immiscible polymers with glass transition regions far apart. The interpenetrating polymer network topology can restrict phase separation and result in materials with a broad transition region. Simultaneous polyurethane/polystyrene interpenetrating polymer networks were synthesized by the one-shot route. Different methods of improving the miscibility of the two polymers were investigated. These included the vanation of the crosslink level in both polymer networks, the controlled introduction of internetwork grafting and the incorporation of compatibilizers into the polystyrene network. Dynamic mechanical thermal analysis indicated that the latter two were successful in achieving a compatibilization of the polymer components. With some materials, a high, broad transition region exhibiting a loss factor > 0.3 over more than 135°C was obtained. The morphology observed via transmission electron microscopy ranged from macrophase separated materials in the lightly crosslinked IPNs to a fine, microheterogeneous morphology in the grafted ones. Modulated differential scanning calorimetry measurements confirmed the trend of the glass transition locations observed with dynamic mechanical thermal analysis.     

The Study of Formation of Amphiphilic Network Block Copolymer of <Emphasis Type="Italic">N</Emphasis>-Isopropylacrylamide

The regularities of formation of the structure of amphiphilic network copolymers on radical copolymerization of N-isopropylacrylamide and polyester dimethacrylate are investigated. The kinetic laws of the consumption of functional groups and the increase in the gel content during formation of a crosslinked product are studied. It is shown that the synthesis of crosslinked amphiphilic copolymers proceeds via competing reactions of N-isopropylacrylamide homopolymerization and its copolymerization with polyester dimethacrylate. With the excess of the monofunctional monomer, a homogeneous rubber-like network copolymer is formed, whereas the excess of the bifunctional reagent results in the morphological inhomogeneity of the reaction product.     

Microphase Structure of Oligoesteracrylate Networks Obtained by Anionic Polymerization in Various Solvents

The microheterogeneous structure of network polymers obtained from oligoestercrylates of anionic polymerization has been studied. The parameters of microheterogeneity of these networks were calculated in the basis of wide- and small-angle x-ray diffraction. The causes of a very distinct microheterogeneity of oligoestercrylate gels and a model of microphase structure of such gels were found within the scope of nonlinear thermodynamics of the irreversible processes.     

Structure formation and gelation phenomena in solutions of ternary interpolyelectrolyte complexes

The representative of the new family of mechanically reversible gels is described. The gel is formed by mixing of an aqueous solution of non-stoichiometric interpolyelectrolyte complex of poly (sodium methacrylate) and poly(N-ethyl-4-vinylpyridinium bromide) containing a certain amount of covalent links between oppositely charged polyions, with aqueous solution of poly(potassium vinylsulfate). The gelation mechanism arises to the partial replacement of the electrostatic contacts between the polycation and poly(methacrylate) anion in the original polycomplex with those between the polycation and poly(vinylsulfate) polyanion. The network of the gel is most probably formed by the nodes consisting of covalent links and interpolyelectrolyte double-strand electrostatic clusters, united by poly(sodium methacrylate) tie-chains.     

Formation and transformations of polyelectrolyte gel-ampholyte dendrimer-surfactant ternary complexes

The reactions of complex gels formed via the sorption of a poly(propylenimine) ampholyte dendrimer of the fourth generation by oppositely charged lightly cross-linked polyelectrolyte hydrogels with ionogenic micelle-forming surfactants have been studied. The sorption of surfactant ions likely charged relative to the complexed ampholyte dendrimer by complex gels is associated with two parallel chemical reactions controlled by the concentration of the surfactant and pH which give rise to the formation of network-dendrimer-surfactant tertiary complexes. The reactions of complex gels with surfactant ions likely charged relative to the network polyelectrolyte make it possible at different solution pHs to prepare both negatively and positively charged hydrogels reinforced by disperse particles of the dendrimer-surfactant complex.     

Fluorescence study of peptide and protein containing interpolyelectrolyte complexes

Four polyelectrolyte (PE)-protein and PE-peptide systems were selected for fluorescence experiments. The mode of binding of proteins to PE and structure of forming polycomplexes depends upon the ratio of components and chemical composition of polymer macromolecules. Complex formation of proteins with oppositely charged polycations is realized by the self-assembly of non-stoichiometric polycomplex particles with characteristic composition. These polycomplex particles have a rigid rod-like carcass structures in which protein molecules are practically exposed to the solvent. Two types of ternary polyanion-Cu²⁺-protein polycomplex particles are formed depending on the monomer composition of the copolymer. At higher content of hydrophobic N-isopropylacrylamide monomer unites, the protein globules in the structure of ternary polycomplex particles are densely covered by the shell of a polymer coil and practically “fenced of” from the water environment. At higher content of acrylic acid unites, polycomplex particles have more friable structures in which protein molecules are practically exposed to the solution. The PE-peptide conjugate species can be represented rather as a macromolecule of a segmented (block) copolymer in which the hydrophobic blocks, i.e. the sequences of copolymer and peptide unit pairs, which have formed the covalent and salt bonds alternate with hydrophilic ones, i.e. the sequences of the copolymer chain not participating in the formation of double strand blocks.     

Preparation of Dendrimers from Macromolecular Cores and Papain Immobilization

Recently,stIJdyonpreparationandpotentialapplicationofdendrimersisquiteactivel-3.StrIJcturally,therearealotoffunctionalgroupsonthesurfaceofadendrimer,whicharepossiblyusedtoconnectwithbiocatalystsuchasenZymeandcell.However,inmostcasesthereporteddendrimerswereviscousandcouldhardlybeusedascarrierforenZymeimmobilization.Inordertoobtainsoliddendrimers,amino-poly(ethyleneglycol)[PEG(NH,),]andamino-propylsilicagel[SG(NH,).]wereselectedastWomacroinitiatorcores(MC)toprepareMC-dendrimers(PEG-den…     

Polysiloxane network formation observed by time-resolved small-angle X-ray scattering

Time-resolved small-angle X-ray scattering was observed on systems undergoing gelation. A polysiloxane network was used as a model system, where the polysiloxane network was formed by hydrosylation of VT-M with F4-C. The Flory-Stockmayer model for gelation was found to be satisfactory to describe the polysiloxane network formation. No inhomogeneous distribution of densely crosslinked region exists, and in this respect the gel formed by the polysiloxane network is homogeneous. The invariance of the correlation length ξ evaluated from the Lorenzian term suggests that the local network architecture would not change by gelation.     

Viscoelastic properties of polybutadienes—linear and lightly crosslinked near the gel point

Viscoelastic properties of four linear and three very lightly crosslinked polybutadienes (microstructure about 50% trans) were studied. Of the latter, two had not reached the gel point, and their molecular weight distributions were determined by sedimentation velocity analysis; the third was crosslinked just past the gel point, with only 32% gel fraction present. The crosslinking agent was sulfur. Complex shear compliances were measured over a frequency range from 0.1 to 1000 cps at temperatures from ?70 to 30°C. with a Fitzgerald transducer and a Plazek torsion pendulum; and torsional creep measurements were made over time periods up to about three days. The creep data were converted to the corresponding dynamic viscoelastic functions at very low frequencies by conventional approximation methods. All data were reduced to 25°C. by shift factors calculated from a previously adopted equation of the WLF form. In the transition zone, the viscoelastic properties of linear samples were almost independent of molecular weight. The entanglement spacing, derived from the minimum in the loss tangent and the inflection in the storage compliance, was 130 to 160 chain atoms. The maximum in the retardation spectrum attributable to motions of individual network strands was closely similar to the corresponding maxima for more highly crosslinked vulcanizates previously studied, showing that even in the latter it is associated with entanglement network strands rather than strands between chemical crosslinks. For a linear sample with molecular weight 180,000, the retardation processes disappear at times beyond about 10 sec. at 25°C. With crosslinking short of the gel point (i.e., branching) the slow retardation processes are enormously increased and prolonged to longer times. With further crosslinking through the gel point and beyond, the slow retardation processes decrease progressively in magnitude. Qualitatively, this behavior resembles the sharp maximum in content of highly branched and aggregated molecular species which is predicted at the gel point by crosslinking statistics; but the slow processes (or low-frequency losses) persist farther past the gel point than would be expected on this basis. The steady-state compliances of the linear samples were smaller, but for a sample crosslinked short of the gel point were much larger, than the prediction of the Rouse theory modified for molecular weight distribution.     

Anionic polymerization of ε-caprolactam and its copolymerization with ω-dodecanelactam in the presence of aromatic polyimides

The anionic polymerization of ε-caprolactam in the presence of aromatic polyimides as activators has been studied under adiabatic conditions. It has been shown that despite the crosslinked structure the produced graft copolymers of polycaproamide and polyimides contain the crystalline phase and are characterized by better water resistance and thermal stability, a higher content of the gel fraction, and improved mechanical properties as compared to copolymers prepared under the so-called isothermal conditions. It has been demonstrated that the catalytic system MgBr-ε-caprolactam-aromatic polyimide may be used for the anionic copolymerization of ε-caprolactam with ω-dodecanelactam, and experimental conditions providing a copolymer yield of 75% have been developed.     

水解聚丙烯酰胺柠檬酸铝体系成胶行为与形态结构的研究

采用光学显微镜、扫描电镜及流变性能测试等手段 ,研究了部分水解聚丙烯酰胺 (HPAM )与柠檬酸铝 (AlCA)的成胶行为与形态结构 .结果表明 ,当AlCA浓度超过 10 0mg/L时 ,随HPAM浓度由低向高变化 ,HPAM AlCA交联体系可形成三种不同形态结构的凝胶 :分散凝胶 (由交联聚合物颗粒形成的分散体 )、两相(分散凝胶相与连续网状凝胶相 )共存凝胶和连续网状凝胶 .HPAM AlCA形成分散凝胶时 ,无明显的粘度升高现象 ,但体系中存在由HPAM大分子交联在一起的颗粒结构 .HPAM AlCA在形成连续网状凝胶时 ,体系复模量和复粘度大幅度提高 ,网状凝胶中含有粒状凝胶颗粒 .