Arylamino-derivatives of syndiotactic 1,2-polybutadiene

The chemical modification of syndiotactic 1,2-polybutadiene via interaction of the polymer with aromatic amines in the presence of sodium tetrachloroaluminate Na[AlCl₄] has been studied. With the use of IR and NMR spectroscopy data, the structure of the modified 1,2-polydiene has been examined.     

Chlorine derivatives of syndiotactic 1,2-polybutadiene

It is shown that chlorine-containing polymeric products may be produced on the basis of the syndiotactic 1,2-polybutadiene by incorporating chlorine atoms into macromolecules via double carbon-carbon bonds. The functionalization of the polydiene with halogen atoms markedly changes the viscosity of solutions, flowability of the melt, and thermal stability of polymeric products. Chlorine derivatives of the syndiotactic 1,2-polybutadiene may be used as high-molecular-mass modifiers improving rheological properties of polymeric compounds in poly(vinyl chloride)-based polymeric composites.     

Dichlorocyclopropane derivatives of syndiotactic 1,2-polybutadiene

Polymeric products containing hem-dichlorocyclopropane units with a degree of functionalization of up to 97% are synthesized via the reaction of syndiotactic 1,2-polybutadiene with dichlorocarbene obtained by the interaction of chloroform with an aqueous solution of sodium hydroxide in the presence of a phase-transfer catalyst. The incorporation of dichlorocyclopropane groups into units of polydiene substantially changes its molecular mass and polydispersity, the solution viscosity, the polymer melt flowability, and the glass-transition temperature and flow temperature of the polymer.     

Hydrochlorinated derivatives of syndiotactic 1,2-polybutadiene

Chlorine-containing polymeric products with a degree of functionalization of up to 70% are synthesized through the hydrochlorination of syndiotactic 1,2-polybutadiene via carbon-carbon double bonds. The introduction of chlorine atoms into polydiene units causes substantial changes in the viscosity of polymer solutions, the flowability of the polymer melt, the glass-transition and flow temperatures, and the thermal stability of polymers. The hydrochlorinated derivatives of syndiotactic 1,2-polybutadiene demonstrate good adhesion with respect to steel and can be used in adhesive compositions.     

Epoxidation of syndiotactic 1,2-polybutadiene with peracids

The epoxidation of syndiotactic 1,2-polybutadiene (84 and 16% 1,2 and 1,4 units, respectively) with carboxylic peracids prepared in situ and m-chloroperbenzoic acid was studied. In the course of epoxidation in the presence of carboxylic peracids, oxirane groups are formed only through epoxidation of double bonds in the macromolecular backbone, whereas m-chloroperbenzoic acid is responsible for the chemical modification of 1,2 and 1,4 units of polybutadiene. The basic kinetic parameters of 1,2-polybutadiene epoxidation with peracids of various chemical structures were determined.     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. III. 1H- and 13C-NMR study of highly syndiotactic 1,2-polybutadiene

The ¹H and ¹³C-NMR spectra of highly crystalline syndiotactic 1,2-polybutadiene (s-PB) are discussed in order to clarify the mechanism of butadiene polymerization with cobalt compound–organoaluminum–CS₂ catalysts. Cis opening of the double bonds in the syndiotactic polymerization is affirmed by the study of the copolymer from perdeuteriobutadiene and cis,cis-1,4-dideuteriobutadiene. S-PB (mp 210°C) has 99.7% 1,2 units, 0.3% isolated cis-1,4 units, and 99.6% syndiotacticity. Polymer ends (2-methyl-3-butenyl group and conjugated diene structure) are also determined. The differences in free energy of activation between 1,2 and cis-1,4 propagation and between syndiotactic and isotactic propagation are 14.0 and 9.6 kcal/mol, respectively, for Co(acac)₃-AlEt₃-AlEt₂Cl-CS₂, and 6.7 and 5.7 kcal/mol, respectively, for the aluminum-free Co(C₄H₆)(C₈H₁₃)CS₂ system. The conformation of s-PB in o-dichlorobenzene at 150°C is described by the sequence (tt)_1.6(gg)(tt).     

Viscoelastic and rheological properties of syndiotactic 1,2-polybutadiene

The physicomechanical, viscoelastic, and rheological characteristics of syndiotactic 1,2-polybutadiene were studied and compared with those of the analogs produced in other countries.     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. I. Preparation,properties, and application of highly crystalline syndiotactic 1,2-polybutadiene

Highly crystalline syndiotactic 1,2-polybutadiene (s-PB) having melting point (mp) up to 216°C was obtained by using a Co(acac)₃-AIEt₃-CS₂ catalyst. The polymer with mp 208°C was found to have 99.7% 1,2 content and 99.6% syndiotacticity by ¹H and ¹³C-NMR measurements. The s-PB can be molded by addition of a stabilizer such as 2,6-di-t-butyl-4-hydroxymethylphenol into fiber, film, and various shaped articles. The physical properties presented in the present article include stress-strain and dynamic mechanical behavior. The highly crystalline syndiotactic 1,2-polybutadiene was applied to a carbon fiber and UBEPOL VCR (cis-1,4-polybutadiene reinforced by fibrous syndiotactic 1,2-polybutadiene).     

Thermal degradation of halogen derivatives of syndiotactic 1,2-polybutadiene

Thermal degradation of halogen derivatives of syndiotactic 1,2-polybutadiene, differing in the kind of the halogen, its content in the polymeric product, and its position in the monomeric unit, was studied by thermal gravimetric analysis. Comparative evaluation of the heat resistance of the halogenated polymers under consideration was made.     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. II. Catalysts for stereospecific polymerization of butadiene to syndiotactic 1,2-polybutadiene

Butadiene is polymerized by cobalt compound–organoaluminum–CS₂ catalysts to give highly crystalline syndiotactic 1,2-polybutadiene (s-PB) having melting point up to 216°C. An aluminum-free catalyst, Co(C₄H₆)(C₈H₁₃)-CS₂, is also effective. Syndiotactic polymerization with Co(C₄H₆)(C₈H₁₃)-CS₂ is not interrupted by the addition of protic substances such as water and alcohol, but is influenced by donor or acceptor substances. The donor molecule, e.g., dimethylsulfoxide or dimethylformamide, decreases the stereoregularity, i.e., syndiotacticity and 1,2 content. An acceptor molecule of organoaluminum with appropriate acidity such as AlEt₃-AlEt₂Cl or tetraethylaluminoxane increases the molecular weight, stereoregularity, and yield of the polymer. In the presence of CS₂ a mixture of cis-PB and s-PB was obtained by using Co(octoate)₂-AlEt₂Cl-H₂O, with molar ratio H₂O/Co less than unity. In the case of H₂O/Co > 1, only cis-PB was obtained. By the addition of donor substances such as ester, ether, nitrile, and AlEt₃, s-PB was obtained even when H₂O/Co > 1. The amount and ratio of cis-PB and s-PB are dependent upon the nature and amount of the additives.     

Properties of modified polymers based on syndiotactic 1,2-polybutadiene

The influence of the chemical modification on the properties of syndiotactic 1,2-polybutadiene derivatives that contain various functional groups in macromolecules and show promise for practical use was studied. The dependence of the glass transition point and the fluidity and rheological properties of modified polydiene melts on the nature of the functional group in the macrochain and on the degree of the polymer functionalization was revealed. The possibility of directional synthesis of modified polymer products with the required operation characteristics on the basis of syndiotactic 1,2-polybutadiene was demonstrated.     

The preparation, properties and application of carbon fibers for SPME

The conditions of preparation of new types of carbon fibers for solid phase micro extraction (SPME) prepared by methylene chloride pyrolysis (at 600 °C) on the quartz fiber (100 μm) as well as by supporting synthetic active carbon (prepared especially for this purposes) supported in a special epoxide-acrylic polymer is described. The properties of such carbon fibers for SPME were defined by determination of the partition coefficient of the tested substances (i.e., benzene, toluene, xylenes, trichloromethane and tetrachloromethane) and by the microscopic investigations with the application of the optical and scanning electron microscope.

The obtained carbon SPME fibers were applied to the analysis of some volatile organic compounds from its aqueous matrix. During chromatographic GC test, at the investigated SPME carbon fibers, we obtained different but mostly high partition coefficients for the determined compounds (Kfs from 120 for trichloromethane up to 11,500 for tetrachloromethane).

Owing to the high partition coefficients of the studied substances obtained on carbon fibers, it was possible to do the analysis of organic substances occurring in trace amounts in different matrices. In this paper, we present the analysis of BTX contents in the petrol analyzed with the application carbonized with CH₂Cl₂ SPME fiber (C1NM) and a headspace over the petrol sample (concentration of each BTX g/dm³).     

Synthesis and properties of epoxy derivatives of syndiotactic 1,2-polybutadiene

Samples of modified 1,2-polybutadiene were prepared by the reaction of the polymer with peracetic acid or tert-butyl hydroperoxide in the presence of a catalyst, hexacarbonylmolybdenum. The hydrodynamic characteristics of dilute solutions and the rheological properties of concentrated solutions of the starting and epoxidized polydiene in hydrocarbon solvents were studied. The Huggins constant K _x, second virial coefficient A ₂, root-mean-square size of macromolecular coils $(\overline {R^2 } )^{1/2} $ , and the enthalpy, entropy, and Gibbs energy of activation of the viscous flow of solutions of the starting and modified polydiene were estimated.     

Thermal stability, crystallization, structure and morphology of syndiotactic 1,2-polybutadiene/organoclay nanocomposite

Syndiotactic 1,2-polybutadiene/organoclay nanocomposites were prepared and characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), respectively. The XRD shows that exfoliated nanocomposites are formed dominantly at lower clay concentrations (less than 2%), at higher clay contents intercalated nanocomposites dominate. At the same time, the XRD indicates that the crystal structures of sPB formed in the sPB/organoclay nanocomposites do not vary, only the relative intensity of the peaks corresponding to (0 1 0) and (2 0 0)/(1 1 0) crystal planes, respectively, varies. The DSC and POM indicate that organoclay layers can improve cooling crystallization temperature, crystallization rate and reducing the spherulite sizes of sPB. TGA shows that under argon flow the nanocomposites exhibit slight decrease of thermal stability, while under oxygen flow the resistance of oxidation and thermal stability of sPB/organoclay nanocomposites were significantly improved relative to pristine sPB. The primary and secondary crystallization for pristine sPB and sPB/organoclay (2%) nanocomposites were analyzed and compared based on different approaches. The nanocomposites exhibit smaller Avrami exponent and larger crystallization rate constant, with respect to pristine sPB. Primary crystallization under isothermal conditions displays both athermal nucleation and three-dimensional spherulite growth and under nonisothermal processes the mechanism of primary crystallization becomes very complex. Secondary crystallization shows a lower-dimensional crystal growth geometry for both isothermal and nonisothermal conditions. The activation energy of crystallization of sPB and sPB/organoclay nanocomposites under isothermal and nonisothermal conditions were also calculated based on different approaches.     

GeO2 fibers: preparation, morphology and photoluminescence property

Nanomicron to submicron fibers of GeO(2) have been prepared using poly(vinyl acetate) and germanium dioxide sol by electrospinning followed by high temperature calcination. The morphology of the fibers have been studied by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. X-ray diffraction indicates that the fibers are single crystal with hexagonal alpha-phase quartz-like structure. At room temperature, the fibers show photoluminescence under excitation at 325 nm. The fibers may have potential applications in one-dimensional optoelectronic nanodevices.     

Melt spinning of poly(3-hydroxybutyrate) fibers for tissue engineering using alpha-cyclodextrin/polymer inclusion complexes as the nucleation agent

This paper reports on an attempt to use CD and CD/PHB ICs as nucleation agents for PHB in a high-speed melt spinning process. At first rheological and thermal properties of the nucleated melts are determined in order to assess the influence of the nucleating agents. Then spinning tests are carried out. Thermal and textile properties of the spun PHB fibers are also determined. An estimation of the improvement of inhibition of the secondary crystallization from use of the described blood compatible nucleating agents is given.     

A simple method for the preparation of activated carbon fibers coated with graphite nanofibers

A simple method is described for the preparation of activated carbon fibers (ACFs) coated with graphite nanofibers (GNFs). Low-pressure-plasma mixed-gas (Ar/O2) treatment of the ACFs led to the growth of GNFs on their surface. The growth was greater at higher power inputs, and from TEM observations the GNFs were seen to be of herringbone type. It was found that the N2 adsorption capacity of the ACFs did not sharply decrease, and that volume resistivity of the ACFs enhanced as a result of this treatment.     

Melt spinning and mechanical properties of semirigid liquid-crystal copolyesters

Melt-spinning and mechanical properties of fibers of a new class of semirigid thermotropic liquid-crystal polymers are presented. These copolyesters are synthesized from 4-4′-dihydroxybiphenyl (B), 4-hydroxybenzoic acid (H), and flexible units provided by aliphatic diacids. The flexible units depress the melting temperature without strongly depressing the mechanical properties. These liquid-crystal polymers can be easily spun at high draw ratios. Indeed, unlike rigid liquid-crystal polymers, relatively high draw ratios are needed to attain high mechanical strength. Tensile moduli of about 28 GPa and tensile strengths of about 350 MPa are obtained. © 1993 John Wiley & Sons, Inc.