Effect of fullerene C60 branching center on the conformational properties of arms and the structure of star-shaped polystyrenes in solutions

The effect of the fullerene C₆₀ branching center on the structure and conformation of star-shaped polystyrenes with different arm lengths at equal concentrations in deuterotoluene (c = 1 g/dL) is studied by the method of small-angle neutron scattering. The analysis of neutron scattering for linear PS precursors and stars (the molecular masses of arms are ～7 × 10³ and ～4 × 10⁴) shows that the stars have ～6 arms that form a dense excluded-volume zone around a core inaccessible to other macromolecules. In low-molecular-mass stars (the molecular mass of the arm is ～7 × 10³), strengthening of the static rigidity of arms is observed; as a result, the size of arms increases relative to the size of free PS chains in a good solvent. At a greater length of arms (M ～ 4 × 10⁴), their individual properties are weakly pronounced in the correlation spectrum of the arm because of the interpenetration of arms, thereby demonstrating similarity in the structures of stars and their linear analogs. The mechanism controlling the effect of fullerene C₆₀ on the conformations of stars via solvent structuring by fullerene is discussed.     

Hydrodynamic and conformational properties of a hyperbranched polymethylallylcarbosilane in dilute solutions

The hydrodynamic and conformational properties of a hyperbranched polymethylallylcarbosilane in hexane solutions have been studied by light scattering, sedimentation, translational diffusion, and viscometry. Fractions with M = (1–75) × 10³ have been used in experiments. The solution behavior of the hyperbranched polymer significantly differs from the properties of both spherical particles and linear polymers. The shape of hyperbranched polymethylallylcarbosilane macromolecules differs from spherical—the asymmetry factor is p ≤ 1.5. Polymethylallylcarbosilane macromolecules in solutions are characterized by compact structure—the hydrodynamic radius is not higher than 4 nm at M = 75 × 10³.     

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.     

Synthesis and properties of hyperbranched copolymers based on perfluorinated germanium hydrides

Hyperbranched copolymers of various structures and molecular masses in the range 2.0 × 10⁴?4.4 × 10⁵ are prepared via the activated copolycondensation of tris- and bis(pentafluorophenyl)germane in tetrahydrofuran performed in the presence of triethylamine as an activator. The kinetics of copolycondensation is studied via the method of heat-conduction reaction calorimetry. It is found that tris(pentafluorophenyl)germane shows a higher activity in copolycondensation than bis(pentafluorophenyl)germane. Shear moduli, loss factors, and glass-transition temperatures of the copolymers are determined by dynamic mechanical analysis and differential-scanning calorimetry. The copolymers feature glass-transition temperatures up to 250°C. These values are considerably higher than those of perfluorinated polyphenylenegermane (162°C).     

Molecular and hydrodynamic characteristics of star-shaped polystyrenes with one or two fullerene (C<Subscript>60</Subscript>) molecules as a branching center

The molecular properties of regular star-shaped polystyrenes with different numbers of arms (6, 12, and 22) and different structures of the branching center (one or two covalently bonded fullerene C60 molecules) are studied by static light scattering; translational diffusion; and viscometry in toluene, THF, and chloroform. The lengths of the arms for the studied polymer stars are found to be the same. (The molecular mass of the arm is 8.1 × 10³.) The molecular mass and hydrodynamic sizes of macromolecules are estimated. It is shown that the conformational and hydrodynamic characteristics of polymer stars remain practically unchanged on passage from THF to chloroform. Compared to the linear analog, star-shaped fullerene-containing PSs are characterized by a higher density of the molecular coil. The shape of their macromolecules differs insignificantly from spherical, in consistence with theoretical predictions for polymer stars with relatively short arms.     

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.     

Macromolecular properties and topological structure of spruce dioxane lignin

Samples of spruce dioxane lignin were isolated by means of six-stage extraction from spruce sawdust, their macromolecular characteristics were determined, and the hydrodynamic properties of the fractions were studied. The conformational properties and the topological structure of dioxane lignin were characterized. The heterogeneity of spruce dioxane lignin isolated in the successive steps of organosolv delignification was established, a property that is confirmed by the variability of the Tsvetkov-Klenin hydrodynamic invariant and a departure from linearity of the logarithmic dependence of the diffusion coefficient on the molecular mass. It was assumed that dioxane lignin macromolecules exist as branched polymers at M _w< 2 × 10⁴ and a network structure is formed at M _w > 2 × 10⁴.     

Dynamooptical and electrooptical properties of poly(methylphenylsiloxane) in solution and bulk

The dynamooptical, electrooptical, and hydrodynamic properties of a low-molecular-mass poly(methylphenylsiloxane) containing 33% phenyl radicals (with respect to the total amount of side groups) in dilute solutions and in bulk are studied. The size of macromolecules, as well as the molecular mass of the polymer, its shear optical coefficients Δn/Δτ = (0.29 ± 0.3) × 10^?10 (in decalin) and (0.43 ± 0.03) × 10^?10 cm s²/g (in bulk), and the specific Kerr constants K = (2.30 ± 0.02) × 10^?12 (in benzene), (2.23 ± 0.02) × 10^?12 (in decalin), and (2.24 ± 0.09) × 10^?12 cm⁵/[g (300 V)²] (in bulk), are estimated and compared with the corresponding characteristics of poly(dimethylsiloxane). The effect of solvents on the intramolecular mobility, optical anisotropy, and dipole structure of polymer macromolecules is considered.     

Direct two-step synthesis of <Emphasis Type="Italic">n</Emphasis>-butyl acrylate–acrylic acid block copolymer by RAFT polymerization

A series of narrow-MMD polymers with the molecular mass from 33 × 10³ to 123 × 10³ (polydispersity coefficient 1.08–1.16) were synthesized by bulk polymerization of n-butyl acrylate [2,2′-azobis(isobutyronitrile), 60°C] in the presence of a low-molecular-mass RAFT agent, dibenzyl trithiocarbonate. Then, polymerization of acrylic acid was performed in aqueous-alcoholic solution (ammonium persulfate, 70°C) in the presence of the obtained polymers, and a series of n-butyl acrylate–acrylic acid block copolymers with the molecular masses from 22 × 10³ to 81 × 10³ (polydispersity coefficient 1.07–1.13) were prepared. In aqueous-alcoholic solutions of the synthesized copolymers, there are nanoparticles whose size varies from 5 tо 65 nm and increases with an increase in the molecular mass of the copolymer and in the concentration of water in the solvent.     

Preparation,characterization and morphological study of poly(<Emphasis Type="Italic">m</Emphasis>-toluidine-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="Italic">m</Emphasis>-aminoacetophenone) conductive copolymer

A new series of copolymers of poly(m-toluidine-co-m-aminoacetophenone) were synthesized by the chemical oxidative method in acid medium. The copolymers were characterized by UV–Vis and FTIR spectroscopy. X-ray diffraction analysis revealed the partial crystalline nature of copolymer. The morphological study by SEM analysis indicated that the surface of the copolymer had the granular structure of agglomerated morphology with average particle size of 200 nm. The conductivity of the copolymers ranged from 2 × 10^–4 to 3.3 × 10^–8 S/cm and the conductivity decreased with the increase of comonomer concentration. The resultant copolymers showed an enhanced solubility and an improved processability when compared with pure polyaniline.     

Properties of Methacrylic Acid–Methyl Acrylate Copolymers of Varied Structure

Physicomechanical and surface properties of films of copolymers of methacrylic acid with methyl acrylate, which have close compositions and molecular masses (M_n ≈ 5.7 × 10⁴) and various chain structures (gradient copolymer and statistical copolymer), were studied. The thermodynamic characteristics of the copolymers were determined; two glass-transition points (29.6 and 141.0°C) were found for the gradient copolymer, and one glass-transition point of 40.1°C, for the copolymer with a statistical distribution of units along the chain. It was found that more mechanically strong films with tensile stress of 2.8 MPa are characteristic of the gradient copolymer. The wetting method was used to determine by using the Hood–Kaelble–Dann–Fowkes approach the surface Gibbs energies of the films and their polar and dispersion components. Atomic-force microscopy was used to find heterogeneities (0.1–0.3 μm) on the surface of a film of a statistical copolymer, whereas the film of a gradient polymer has a homogeneous structure.     

Solution properties of styrene-p-chlorostyrene diblock copolymers—II. Light scattering studies in a selective solvent

Conformational behaviour of styrene-p-chlorostyrene diblock copolymers in cumene (a good solvent for polystyrene but a θ solvent for poly-p-chlorostyrene) was studied over the temperature range 15–60° by light scattering, osmotic pressure and intrinsic viscosity measurements. Two samples of copolymer (AB-4 and AB-2) were used. The composition of the samples was c. 50 mol% of styrene and the number-average molecular weights were 27.7 × 10⁴ for the AB-4 and 19.5 × 10⁴ for the AB-2. It was found that below 40° the number-average molecular weight of the AB-4 sample seemed to increase gradually with decreasing temperature and around 40°, marked decreases in the osmotic second virial coefficient and intrinsic viscosity were observed. The Zimm plot for the AB-2 sample was fairly normal at 40°. It seems that the temperature where an anomaly becomes evident in Zimm plots is dependent on the molecular weight of the sample. The experimental results for the diblock copolymers could be understood from the view that intermolecular association took place to some extent in the solutions on lowering the temperature giving rise to multi-molecular micelles.     

Bidentate Pyridyl-Amido Hafnium Catalysts for Copolymerization of Ethylene with 1-Octene and Norbornene

Polyolefin elastomers ( POEs ) and cyclic olefin copolymers ( COCs ) are high-performance polyolefin materials of wide interest. It is crucial to develop low-cost and high-performance transition metal catalysts to prepare these polyolefin materials. In this contribution, we designed and synthesized a series of bidentate pyridyl-amido hafnium catalysts and used them in ethylene polymerization and copolymerization with comonomers including 1-octene and norbornene. These catalysts exhibited high activities of up to 16.3×10⁶ g mol⁻¹ h⁻¹ and produced polyethylene with a high molecular weight of up to 24.5×10⁴ g mol⁻¹ in ethylene polymerization at 150 °C. More importantly, these catalysts produced ethylene/1-octene copolymers with incorporation of up to 13.7 mol % and molecular weight of up to 72.7×10⁴ g mol⁻¹, and prepared ethylene/norbornene copolymers with incorporation of up to 50.3 mol %, along with glass transition temperature of up to 184.3 °C and molecular weight of up to 187.6×10⁴ g mol⁻¹. The ease of synthesis, high versatility and great copolymerization properties of these hafnium catalysts make them highly attractive for future studies.     

INFLUENCES OF MOLECULAR WEIGHT AND BRANCHING PARAMETER OF LACQUER POLYSACCHARIDE ON THE GROWTH OF LEUCOCYTES

A method of determining branching parameter of lacquer polysaccharide wasestablished by acid-base back-titration of terminal uronic acid of branches. The branchingfactors obtained are in agreement with the values determined by colorimetric method withcarbazole and the results estimated by using Zimm-Stockmayer equation from viscositydata. Influences of molecular weights and branching factors of five fractions of lacquerpolysaccharide on the bioactivities were studied. The results show that the polysaccharideshave bioactivities in motivating the growth of leucocytes, and the effect increases with thedecrease of molecular weight and branching factor in the range studied (17×10~4 >M_w>4×10~4).     

STUDY ON CATIONIC RING-OPENING POLYMERIZATION MECHANISM OF 3-ETHYL-3-HYDROXYMETHYL OXETANE

ABSTRACT

Cationic ring-opening polymerization of 3-ethyl-3-hydroxylmethyl oxetane was carried out using BF₃·O(C₂H₅)₂ as initiator, and a branched polyether was formed. Typical SEC curves show that the polymer consists of two fractions: one has higher molecular weight (11.7×10⁴～ 9.2×10⁴) and the other has lower molecular weight (3.8×10³～4.0×10³). This probably resulted from the chain-tran sfer reaction of two propagating polymer chains. The structure of the polyEHMO formed was characterized by ¹H and ¹³C NMR spectra. The degree of branching is mainly affected by the propagation mechanism. As the molar ratio of [I]₀/[EHMO]₀ in feed increased, the degree of branching also increased.     

Copolymerization of N-vinylpyrrole-2-carbaldehydes with styrene, N-vinylpyrrolidone, and ethylene glycol vinyl glycidyl ether

Polyfunctional reactive copolymers of N-vinylpyrrole-2-carbaldehydes with styrene, N-vinylpyrrolidone, and ethylene glycol vinyl glycidyl ether are synthesized in the presence of AIBN (2 wt %, 80°C, 50 h) with a yield of up to 98% and a molecular mass of up to 4800. The copolymers show paramagnetic behavior (N = 2.0 × 10¹⁵?2.0 × 10¹⁷ g^?1) and possess the properties of organic semiconductors (σ = 0.9 × 10^?11–2.8 × 10^?7 S/cm after doping with I₂).     

聚环氧乙烷大单体与丙烯酸乙酯的共聚及其规整接枝共聚物的表征

 本工作研完了末端为甲基丙烯酸酯型的聚环氧乙烷大单体与丙烯酸乙酯的溶液自由基共聚。结果表明,大单体接枝效率和共聚物分子量受单体总浓度、投料比、大单体分子量及引发剂等的影响,接枝效率最高可达90％以上,分子量可在5-15×10⁴范围内变化。丙烯酸乙酯与大单体共聚的竞聚率为0.83。共聚物用萃取法精制后,用IR、¹H-NMR、裂解色谱、GPC和膜渗透压计等进行了表征。证实产物有预期的规整接枝共聚物结构。平均接枝数为2—11。     

Structural features of films based on star-shaped fullerene-containing polystyrenes: Small-angle neutron-scattering study

The structuring of films based on regular six-arm and twelve-arm polystyrenes with the arm characteristics M_n = 118 × 10³ and M_w/M_n = 1.06 and a fullerene (С₆₀) branching center in a weakly swollen state in a mixture of deuterated solvents (90 vol % D-methanol and 10 vol % D-toluene) is studied by small-angle neutron scattering. Analogous studies are performed for films based on linear polystyrene (M_n = 280 × 10³, M_w/M_n = 1.07) and its composites with fullerene С₆₀ (0.5 wt %). It is shown that, during saturation of the samples with the solvent D-toluene, filling of the free volume that forms chain-transport channels that have gyration radii of the order of diameters of macromolecules and unite to form submicron and micron structures occurs. The degree of filling of the free volume, which is maximum for the linear polymer, becomes minimum for polystyrene with the inserted free fullerene. In addition, the transition from the linear polymer to the six-arm polymer is related to a smaller degree of filling of the free volume due to the formation of thinner migration channels. As the amount of arms in macromolecules is increased to 12, permeability of the polymer matrix improves because molecular order partially appears in accordance with the model of the densest packing of solid spheres.     

Internal organization and conformational characteristics of star-shaped polystyrene with fullerene C<Subscript>60</Subscript> as a branching center in deuterotoluene

The internal organization of star-shaped polystyrene macromolecules containing fullerene C₆₀ as a branching center is studied via small-angle neutron scattering in deuterotoluene. Analysis of the experimental data according to the Debye-Benoit approximation and the Fourier transformation of the momentum transfer dependences of scattering cross sections for the linear PS precursor and stars is used to determine their molecular masses (9 × 10³ and 5 × 10⁴) and gyration radii (∼2.7 and ∼5.5 nm), the gyration radius of the arm (∼3.4 nm), and the average functionality of the star (5.7). The behavior of scattering cross sections for the fullerene-containing polymer on the whole is described by the law of scattering for stars with Gaussian arms (the Benoit model). However, at the local level (within one chain segment), the fullerene center exerts a specific effect on the conformation of arms. As a result, their statistical flexibility decreases and eventually the size of the star increases by ∼30%. This finding conflicts with the Daoud-Cotton theory.     

Synthesis of side‐chain liquid‐crystalline homopolymers and triblock copolymers with p‐methoxyazobenzene moieties and poly(ethylene glycol) as coil segments by atom transfer radical polymerization and their thermotropic phase behavior

A series of side‐chain liquid‐crystalline (LC) homopolymers of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with different degrees of polymerization were synthesized by atom transfer radical polymerization (ATRP), which were prepared with a wide range of number‐average molecular weights from 5.1 × 10³ to 20.6 × 10³ with narrow polydispersities of around 1.17. Thermal investigation showed that the homopolymers exhibit two mesophases, a smectic phase, and a nematic phase, and the phase‐transition temperatures of the homopolymers increase clearly with increasing molecular weights. A series of novel LC coil triblock copolymers with narrow polydispersities was synthesized by ATRP, and their thermotropic phase behavior was investigated with differential scanning calorimetry and polarized optical microscopy. The LC coil triblocks were designed to have an LC conformation of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with a wide range of molecular weights from 3.5 × 10³ to 1.7 × 10⁴ and the coil conformation of poly(ethylene glycol) (PEG) (number‐average molecular weight: 6000 or 12,000) segment. Their characterization was investigated with ¹H NMR, Fourier transform infrared spectra, and gel permeation chromatography. Triblock copolymers exhibited a crystalline phase, a smectic phase, and a nematic phase. The phase‐transition temperatures from the smectic to nematic phase and from the nematic to isotropic phase increased, and the crystallization of PEG depressed with increasing molecular weight of the LC block. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2854–2864, 2003