Star-shaped polymers with a doubled fullerene (C60) branching center

Star-shaped regular homopolystyrenes with 22 arms and heteroarm polymers with 12 PS arms and 10 poly(2-vinypyridine) arms have been synthesized by consecutive coupling-functionalization-coupling reactions. The synthesis includes the following stages: the exhaustive grafting of fullerene C₆₀ by polystyryllithium chains (living hexaadducts); the coupling of hexaadducts with the use of dimethyldichlorosilane or 1,4-dibromobutane into twelve-arm macromolecules, where the branching center is composed of two covalently bonded fullerene C₆₀ molecules; functionalization of twelve-arm double-core PS stars during the action of excess dihalides (the replacement of lithium atoms with groups containing chlorine or bromine atoms); and the coupling of living chains of PS or poly(2-vinylpyridine) via reactions with halogen-containing groups at the branching center of double-core PS stars. Linear living polymers used as arms have been prepared by anionic polymerization. Exclusion chromatography has been used to control the individual stages of synthesis. The molecular characteristics of the PS precursor and of star-shaped polymers have been studied in terms of hydrodynamics and light scattering.     

Structure and supramolecular structures of star-shaped fullerene-containing heteroarm polymers in deuterotoluene

Self-organization of star-shaped polymers containing six PS arms and six polar polymer arms on a common C₆₀ branching center is studied by means of small-angle neutron scattering in deuterotoluene. The results are compared with the corresponding characteristics of six-arm star-shaped fullerene-containing PSs. It is shown that the incorporation of additional polar arms into a six-arm macromolecule leads to its compression due to an increase in the degree of coiling of polar chains in the nonpolar solvent. In solution, heteroarm stars give rise to supramolecular structures in the form of clusters whose dimensions and density depend on the nature of the polar arms. Stars containing PS and poly(2-vinylpyridine) arms are weakly associated, and the mean number of particles in an associate is ∼1.3. Hybrid polymers containing PS and poly(tert-butyl methacrylate) arms demonstrate capability for mutual penetration that favors the appearance of large structures that have a diameter of ∼50 nm and that include up to 12 macromolecules. Hybrid stars containing PS and diblock copolymer (poly(2-vinylpyridine)-poly(tert-butyl methacrylate)) arms exhibit moderate self-organization that manifests itself in the formation of chain associates built from four macromolecules.     

Structural features and initiating properties of the hexaadduct of polystyryllithium and fullerene C60 in tetrahydrofuran and their role in synthesis of heteroarm star-like polymers

Structural transformations of the hexaadduct of polystyryllithium and fullerene C₆₀ in the course of interaction with a proton donor or 1,1-diphenylethylene and at initiation of styrene polymerization were studied, and their role in the formation of heteroarm star-like polymers with C₆₀ center of branching and arms of polystyrene and poly-2-vinylpyridine was elucidated.     

Effect of the length of branches on hydrodynamic and conformational properties of hyperbranched polycarbosilanes

The hydrodynamic and conformational properties of hyperbranched polycarbosilanes with different lengths of branches, namely, poly(methyl(allyl)carbosilane) containing three CH₂ groups between branching centers and poly(methyl(undecenyl)carbosilane) whose branches are composed of 11 CH₂ groups, have been studied in dilute solutions in hexane using the methods of molecular hydrodynamics and optics. Fractions with M < 17.5 × 10⁴ have been used in experiments. The hydrodynamic properties of the above polycarbosilanes differ significantly from those of linear polymers since hyperbranched macromolecules are compact and their shape differs only slightly from spherical. The lengthening of chains between branching centers causes a change in the hydrodynamic characteristics, and the difference between hyperbranched polymers and dendrimers becomes more pronounced. As the length of branches increases, their conformation changes from an extended trans chain to a more or less bent rod.     

Star-shaped polymers with the fullerene C60 branching center

The anionic methods for the synthesis of homo- and heteroarm (hybrid) star-shaped polymers using fullerene C₆₀ aPre considered. The possibilities of fullerene C₆₀ as an agent of combination of living polymer chains and the procedures of transformation of polymer derivatives of C₆₀ (hexaadducts) into polyfunctional macroinitiators of anionic polymerization of vinyl monomers are shown. The methods for functionalization of polymer fullerene derivatives and their combinations into structures of complex controlled architecture are presented. The structural features and initiating properties of the living polymer fullerene derivatives and their role in the formation of heteroarm star-shaped macromolecules with the controlled number of branches and predetermined molecular weight characteristics of the arms are discussed. The hydrodynamic properties of the star-shaped fullerene-containing polymers are considered. The data on the small-angle neutron scattering study of self-organization of the stars in solutions are presented.     

Synthesis and characterization of “umbrella” shaped polymers

A new strategy has been developed to prepare umbrella polymer, i.e. star polymers with one heteroarm. The synthesis uses living anionic polymerization to prepare a short segment of 1,2-polybutadiene at the end of a linear polystyrene. The vinyl groups of 1,2-polybutadiene are hydrosilylated with dichloro(methyl)silane. The umbrella polymer is then formed by nucleophilic displacement of the silicon-chlorine with 1,4-polybutadienyllithium. An umbrella polymer with poly(2-vinylpyridine) arms is prepared in the same way after hydrosilylation with chlorodimethylsilane. The umbrella polymers are characterized by light scattering, size-exclusion chromatography (SEC), ultraviolet/visible spectroscopy (UV/vis), nuclear magnetic resonance (NMR) and intrinsic viscosity.     

Synthesis of heteroarm star polymers comprising poly(4-methylphenyl vinyl sulfoxide) segment by living anionic polymerization

<正>A series of 3-arm ABC and AA'B and 4-arm ABCD,AA'BC and AA′A″B heteroarm star polymers comprising one poly(4-methylphenyl vinyl sulfoxide) segment and other segments such as polystyrene,poly(α-methylstyrene), poly(4-methoxystyrene) and poly(4-trimethylsilylstyrene) were synthesized by living anionic polymerization based on diphenylethylene(DPE) chemistry.The DPE-functionalized polymers were synthesized by iterative methodology,and the objective star polymers were prepared by two distinct methodologies based on anionic polymerization using DPE-functionalized polymers.The first methodology involves an addition reaction of living anionic polymer with excess DPE-functionalized polymer and a subsequent living anionic polymerization of 4-methylphenyl vinyl sulfoxide(MePVSO) initiated from the in situ formed polymer anion with two or three polymer segments.The second methodology comprises an addition reaction of DPE-functionalized polymer with excess sec-BuLi and a following anionic polymerization of MePVSO initiated from the in situ formed polymer anion and 3-methyl-1,1-diphenylpentyl anion as well.Both approaches could afford the target heteroarm star polymers with predetermined molecular weight,narrow molecular weight distribution (M_w/M_n1.03) and desired composition,evidenced by SEC,~1H-NMR and SLS analyses.These polymers can be used as model polymers to investigate structure-property relationships in heteroarm star polymers.     

Precise Synthesis of New Triblock Co- and Terpolymers by a Methodology Combining Living Anionic Polymers with a Specially Designed Linking Reaction

Five A-B-A′, A-C-A′, B-A-B′, C-A-C′, and C-B-C′ triblock terpolymers with block orders difficult to synthesize by sequential polymerization have been successfully synthesized by a new methodology combining living anionic polymers with a specially designed linking reaction using α-phenylacrylate as the reaction site. Here, A(A′), B(B′), and C(C′) represent groups of polymers (having chain-end anions with different nucleophilicities), which are only polymerizable from A(A′) to B(B′) to C(C′) via sequential polymerization. The corresponding polymers are polystyrene (A) and poly(α-methylstyrene) (A′), poly(2-vinylpyridine) (B) and poly(4-vinylpyridine) (B′) and polymers from methacrylate type monomers like poly(methyl methacrylate) (C), poly(tert-butyl methacrylate) (C′), poly(2-hydroxyethyl methacrylate) (C′), poly(2,3-dihydroxypropyl methacrylate) (C′), and poly(ferrocenylmethyl methacrylate) (C′). Furthermore, three synthetically difficult B-A-B, C-A-C, and C-B-C triblock copolymers with molecular asymmetry in both side blocks have also been synthesized by the developed methodology. All of the polymers thus synthesized are quite new triblock terpolymers and copolymers with well-defined structures, i.e., precisely controlled molecular weights, compositions and narrow molecular weight distributions (M_w/M_n ≤ 1.05).     

Hydrodynamic, electrooptical, and conformational properties of fullerene-containing poly(2-vinylpyridines) in solutions

For C₆₀ fullerene-containing poly(2-vinylpyridines) synthesized by anionic polymerization, the molecular mass and hydrodynamic size of macromolecules in solutions have been determined by molecular hydrodynamics (translational diffusion and viscometry) and electrooptics in dilute benzene and THF solutions. Under the same conditions in the molecular mass range (9.8–123) × 10³, the hydrodynamic behavior of linear poly(2-vinylpyridines) and their molecular-mass dependences have been examined and the conformational characteristics of macromolecules have been established. The branching of macromolecules has been characterized by comparing the properties of star-shaped fullerene-containing and linear poly(2-vinylpyridines). With consideration of the hydrodynamic data interpreted within the framework of regular star model, it is inferred that on average three to four linear polymer chains with a molecular mass of (8 ± 3) × 10³ for each chain are attached to a fullerene core of C₆₀ in molecules of fullerene-containing poly(2-vinylpyridines). The specific Kerr constant of fullerene-containing poly(2-vinylpyridines) in dilute benzene solution is ?(14 ± 1) × 10^?12 cm⁵/[g (300 V)²]. As evidenced by the electrooptical data, the incorporation of fullerene into the polymer weakens self-association of macromolecules in solution.     

Anionic Synthesis of Heteroarm,Star-Branched Polymers. Scope and Limitations

Abstract

The scope and limitations of the following methods for the synthesis of heteroarm star-branched polymers are presented: (a) divinylbenzene linking reactions; (b) coupling reactions with macromolecular silyl halides; and (c) 1,1-diphenylethylene-based living linking reactions. The methodology of using l, 3-bis(1-phenylethenyl)benzene to prepare A₂B₂ hetero 4-armed stars is reviewed, and the synthesis of well-defined (polystyrene)₂(1,4-polybutadiene)₂ heteroarm stars is described. The synthesis of well-defined ABC heteroarm star polymers using macromonomers functionalized with 1, 1-diphenylethylene groups is described.     

Structural rigidity control in arborescent graft polymers

Successive chloromethylation-anionic grafting sequences on polystyrene have led to well-defined hyperbranched macromolecules. Polymers with branching functionalities f > 5000 and molar masses over 10⁷ g/mol were thus prepared while maintaining a ratio of mass- to number-average molar masses M_w/M_n = 1,1-1,3. Three series of styrene polymers were prepared by varying the density of grafting sites along the chain, resulting in controllable stiffening of the molecular structure. Characterization of the branched molecules by size-exclusion chromatography/low-angle laser light scattering and light scattering confirmed a geometric increase in molar mass for successive generations, and a low ratio of mass- to number-average molar masses. Static and dynamic light scattering experiments showed that the molecules behave like hard spheres in dilute solutions. Measurements in the semidilute range, however, showed a progressive structural stiffening effect as the branching density increases.     

The influence of the molecular mass of two incompatible polymers on their miscibility in the solid state without compatibilizer after casting from solution

The influence of the molecular mass of two incompatible polymers on their miscibility in the solid state has been studied using Scanning Electron Microscopy and Optical Microscopy. Two pairs of incompatible polymers, polystyrene/poly(methyl methacrylate) and polystyrene/poly(oxyethylene) were cast from a nonselective solvent. When the two polymers are of comparable and relatively high molecular mass (M_w ∼ 60,000) we obtain films in which the domains of the two phases are reduced to 7 μm, without the use of any compatibilizer. On the contrary, when the two polymers present very different molecular masses, a lamellar structure is obtained due to the high repulsion between them. This repulsion has already been observed in solution (Refs. 4 and 5). In the case of polymers with comparable but very low molecular masses the repulsion between them, in solution, is also high, leading to phase separation in the films obtained after removal of the solvent. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 379–387, 1999     

Molecular mass characteristics and hydrodynamic and conformational properties of hyperbranched poly-L-lysines

Hydrodynamic and conformational properties of hyperbranched poly(amino acids) based on lysine have been studied by static and dynamic light scattering, velocity sedimentation, translational diffusion, and viscometry in dilute aqueous-saline solutions (0.2 M NaCl). The effects of synthesis conditions of hyperbranched poly(amino acids), modification of their end groups by histidine fragments, and incorporation of diacylated lysine residues between branching points of oligomers and polymers composed of lysine and glutamic acid on the molecular mass characteristics of the hyperbranched polymers have been ascertained. The hydrodynamic properties of the hyperbranched poly(amino acids) differ appreciably from the behavior of both linear polylysine and lysine dendrimers due to conformational features of their macromolecules.     

From smart polymer molecules to responsive nanostructured surfaces

A heteroarm star block copolymer made from seven polystyrene and seven poly(2-vinylpyridine) arms was grafted onto a solid substrate to fabricate a responsive polymer surface consisting of a densely packed monolayer of copolymer molecules. The grafted layer demonstrates a two-level hierarchical response upon external stimuli combining core-shell transitions of single stars with cooperative transitions of the interacting arms between "dimple" and "ripple" morphologies of the monolayer. The response allows for the switching of the surface properties upon changing solvent selectivity or pH of the aqueous environment.     

Preparation of Graft Copolymers By Means of Uv Photolysis of Poly(Methyl Vinyl Ketone) and Reverse Osmosis Performance of the Membranes from the Oximes of the Copolymers

ABSTRACT

An attempt was made to prepare a graft copolymer consisting of poly(methyl vinyl ketone) (PMVK) as a backbone chain and polyacrylonitrile, poly(4-vinylpyridine), or polystyrene as a graft chain by UV irradiation of a solution of PMKV in the presence of acrylonitrile, 4-vinylpyridine, or styrene. the influence of reaction conditions on the yield, composition, and viscosity of the resulting graft copolymers was investigated. It was suggested from NMR and gel permeation chromatography that those graft copolymers contained a high molecular weight fraction of narrow distribution and block copolymers as well. the reverse osmosis membranes derived from the oxime and amidoxime of the graft copolymers showed a characteristic performance of exhibiting a maximal difference between rejections against NaCl and CoCl₂ at a certain addition ratio of crosslinking agent, which was not observed in the membranes from copolymers by conventional radical copolymerization. the relationship between these phenomena and the branching structure of the graft copolymers was discussed.     

Stereoregularity of poly(2-vinylpyridine) and poly-(4-vinylpyridine)

In order to determine the stereoregularity of poly(4-vinylpyridine), 4-vinylpyridine-β,β-d₂ was synthesized from 4-acetylpyridine. The ¹H-NMR spectra of the deuterated and nondeuterated polymers were measured and analyzed. From the ¹H-NMR spectra of poly(4-vinylpyridine-β,β-d₂), triad tacticity can be obtained, while the ¹H-NMR spectra of nondeuterated poly(4-vinylpyridine) give the fraction of isotactic triad. The ¹³C-NMR spectra of poly(4-vinylpyridine) were also observed, and the spectra of C₄ carbon of polymers were assigned by the pentad tacticities. The fraction of isotactic triad of poly(2-vinylpyridine) and poly(4-vinylpyridine) obtained under various polymerization conditions were determined. The radical polymerization and anionic polymerizations with phenylmagnesium bromide and n-butyllithium as catalysts of 4-vinylpyridine gave atactic polymers.     

Anionic synthesis of polystyrene and polybutadiene heteroarm star polymers

The use of living linking reactions of poly(styryl)lithium with 1,3-bis(1-phenylvinyl)benzene followed by crossover reactions with styrene or butadiene monomers has been used to prepare four-armed heteroarm, star-branched polymers. Bimodal molecular weight distributions have been observed for crossover reactions with both styrene and butadiene. Addition of THF ([THF]/[Li]=14–32) for crossover to styrene and lithium sec-butoxide for crossover to butadiene produces monomodal molecular weight distributions. Symmetrical, four-armed star polystyrenes have been synthesized; properties have been compared with a corresponding polymer prepared via a silicon tetrachloride linking reaction. Heteroarm, star-branched polymers with two polystyrene arms and two polybutadiene arms with high 1,4-microstructure have been prepared.     

Core-shell-corona au-micelle composites with a tunable smart hybrid shell

Micelles having a core of polystyrene and a mixed shell of poly(ethylene glycol) and poly(4-vinylpyridine) were formed through self-assembly of a triblock copolymer poly(ethylene glycol)- block-polystyrene- block-poly(4-vinylpyridine) in acidic water (pH 2). Reducing the HAuCl(4)-treated micelle solution leads to the formation of the Au-micelle composites with a core of polystyrene, a hybrid shell of poly(4-vinylpyridine)/Au/poly(ethylene glycol), and a corona of poly(ethylene glycol). The gold nanoparticles with controlled sizes were anchored to poly(4-vinylpyridine) to form the physically cross-linked hybrid shell. In aqueous solution, the hybrid shell is swollen and the swollen degree is sensitive to the pH condition. Under basic conditions, the channel in the hybrid shells of the composite is produced, which renders the composites a good catalytic activity. In addition, the composites also show good stability, unchanged hydrodynamic diameter, and surface plasmon absorption under different pH conditions.     

Triblock and Radial Star-Block Copolymers Comprised of Poly(ethoxyethyl glycidyl ether), Polyglycidol,Poly(propylene oxide) and Polystyrene Obtained by Anionic Polymerization Initiated by Cs Initiators

The anionic polymerization of ethoxyethyl glycidyl ether (EEGE) initiated by cesium alkoxide was studied. The ring-opening polymerization of EEGE in the presence of cesium alkoxide of 1-methoxy-2-ethanol does not involve any side reactions. The presence of an additional alcohol leads to a significant increase of the initiator efficiency. Aqueous solutions of poly (ethoxyethyl glycidyl ether) (PEEGE) exhibit lower critical solution temperature (LCST), and the polymer solubility in water is extremely sensitive to its MW. Two novel types of block copolymers based on PEEGE were synthesized: triblock-copolymers of ABA (A′:BA′) structure, where A is the PEEGE block, A′ polyglycidol (PG) and B the polypropylene oxide (PPO) block, and A₂S (A′₂S) and A₄S (A′₄S) heteroarm stars, where S is the polystyrene block. The synthesis of the ABA block was performed by polymerization of EEGE initiated by bi-functional PPO/Cesium alkoxide macroinitiator. The PEEGE blocks were converted into PG blocks by successful cleavage of the ethoxyethyl group. Polystyrene/PEEGE and polystyrene/PG three- and five- heteroarm star copolymers were synthesized by a coupling reaction between well-defined chain-end-functionalized polystyrenes carying dendritic benzyl bromide moieties with living anionic polymers of PEEGE with one cesium alkoxide terminal group. The coupling reaction proceeds quantitatively without any side reactions, and thus series of star-branched polymers can be systematically synthesized. Polystyrenes with two or four PG arms have been obtained after the cleavage of the protecting group. The compact structure of these multi-arm star polymers and their amphiphilic character leads to the formation of nanoparticles in aqueous solution with rather uniform size distribution and a mean diameter of 15 nm.     

Conformations of sodium poly(styrene-4-sulfonate) macromolecules in solutions with different ionic strengths

Translational friction and viscosity of dilute solutions of sodium poly(styrene-4-sulfonate) with molecular masses of M = (5 × 10⁴)−(85 × 10⁴) are studied at different concentrations of low-molecular-mass salts. Molecular masses of the polymer are determined from the sedimentation-diffusion data. The study of the correlation between molecular masses and hydrodynamic characteristics resulted in ascertainment of the Kuhn-Mark-Houwink-Sakurada relationships for salt-free aqueous solutions of the polymer and solutions of the polymer in 0.2 M NaCl, 4.17 M NaCl, and 1.0 M KCl. It is shown that, as the ionic strengths of solutions are varied from minimum (H₂O) to maximum (4.17 M), macromolecules of the strong polyelectrolyte sodium poly(styrene-4-sulfonate) change their conformations from rigid rods to coils and, then, approach a globular conformation. In terms of the Gray-Bloomfield-Hearst and Yamakawa-Fujii theories and within the framework of the weakly bent cylinder model, the statistical Kuhn segment length and the hydrodynamic diameter of sodium poly(styrene sulfonate) chains are estimated in 0.2 and 4.17 M NaCl, 1.0 M KCl, and salt-free aqueous solutions. The electrostatic component of the equilibrium rigidity is taken into account within the framework of the Odijk-Fixman-Skolnick and Dobrynin theories.