High Molecular Weight Polybutadiene Research Articles

Anti-turbulent efficiency of oil-soluble polymer solutions and colloid systems flowing through cylindrical channel

Relevance. The use of anti-turbulent additives for transporting hydrocarbon liquids through main pipelines allows reducing significantly the energy consumption of pumping power stations. Aim. Comparative analysis of the anti-turbulent efficiency of high-molecular polymers and compositions of surfactants. Methods. Laboratory-scale experimentation aimed to study the flow of dilute polymer solutions and dispersed surfactant systems through a cylindrical channel of a turbulent rheometer. Results. The author has carried out the comparative experimental studies of the anti-turbulent efficiency of extremely dilute solutions of polymers and colloidal systems. The results were obtained that suggest a higher anti-turbulent efficiency of high-molecular-weight polymers compared to micellar surfactant systems. Solutions of high molecular weight polybutadiene and aluminum polyhydroxydicarboxylates in gasoline were used as samples for the experimental comparison of hydrodynamic efficiency. The paper describes the laboratory setup, on which the studies were carried out, and introduces the formulas used for quantitative calculations. The structure of polymer solutions and colloidal systems is considered and a theoretical explanation is given for the preferential use in industrial practice of high-molecular polymers in extremely low concentrations in real pipelines. It was found out that the mechanisms of degradation of antiturbulent properties of polymer solutions and dispersed surfactant systems are different. This is due to the difference in the structure of macromolar coils of polymer with an immobilized solvent and that of micelles from low molecular amphiphilic compounds. The paper introduces the arguments that explain the degradation of the antiturbulent properties of polymers not by the destruction of carbon-chain macromolecules, but by decomposition in a turbulent flow of the original large associates, consisting of a large number of chains, into individual and smaller macromolecular coils with an immobilized solvent.

Regio- and Stereo-Specific Chemical Depolymerization of High Molecular Weight Polybutadiene and Polyisoprene for Their Analysis by High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Comparison with Pyrolysis-Comprehensive Two-Dimensional Gas Chromatography/Mass Spectrometry, Atmospheric Solid Analysis Probe, Direct Inlet Probe-Atmospheric Pressure Chemical Ionization Mass Spectrometry, and Ion Mobility Spectrometry-Mass Spectrometry.

Polybutadiene (PB) and polyisoprene (PI), the two most common polydienes (PD), are involved in a large number of materials and used in a wide variety of applications. The characterization of these polymers by mass spectrometry (MS) continues to be very challenging due to their high insolubility and the difficulty to ionize them. In this work, a cross-metathesis reaction was used to generate end-functionalized acetoxy ionizable oligomers for the structural deciphering of different commercial PB and PI samples. A cross-metathesis reaction was carried out between polymers and the Z-1,4-diacetoxy-2-butene as a chain transfer agent in dichloromethane using a Hoveyda-Grubbs second-generation catalyst. Well-defined acetoxy telechelic structures were obtained and analyzed by Fourier transform ion cyclotron resonance (FTICR) high-resolution MS. However, after depolymerization, low molar mass polyolefins contained some units with different configurations, suggesting an olefin isomerization reaction due to the decomposition of the catalyst. The addition of an electron-deficient reagent such as 2,6-dichloro-1,4-benzoquinone suppressed this isomerization in the case of both Z- and E-PB and PI. Ion mobility spectrometry-mass spectrometry (IMS-MS) and energy-resolved tandem mass spectrometry (ERMS) analyses confirmed a successful isomerization suppression. For comparing the results obtained by depolymerization with classical methods for polymer analysis, pyrolysis-comprehensive two-dimensional gas chromatography/mass spectrometry (Py-GC × GC-MS), atmospheric solid analysis probe (ASAP), and direct inlet probe-atmospheric pressure chemical ionization (DIP-APCI) analyses were performed on the same polymers. This strategy can be applied on a variety of synthetic and natural not yet characterized polymers.

CoFe2O4 Nano-particles for Radical Oxidative Degradation of High Molecular Weight Polybutadiene

Polymer waste production increased dramatically in the last decades, and has reached to 380 million tons (Mt.) in 2015. Due to their long-term stability, these materials impose a serious environmental challenge. Currently, recycling of polymer waste focuses on re-use of actual products, mechanical processing, chemical recycling, and bio-degradation into environmentally friendly materials. In our previous work, we proposed a new approach for radical-initiated oxidative degradation of polymers using cobalt ferrite (CoFe2O4) nanoparticles. In our current work, we focus on the use of CoFe2O4 nanoparticles as catalysts for radical degradation of high molecular weight polybutadiene. Cobalt ferrite nanoparticles were embedded into the polybutadiene polymeric matrix, with the aim of studying degradation in polymeric products that can be manufactured with catalytic nanoparticles. The polymer degradation process was characterized using gel permeation and size exclusion chromatography measurements, thermogravimetric analysis, FTIR, NMR, and mass spectroscopy. Based on the results from these diverse measurements, we propose a mechanism for the degradation process. Overall, our results show that the radical processes within the polybutadiene polymer lead to two parallel processes: polymer crosslinking and polymer scission. Moreover, we show that the ratio between crosslinking and degradation can be controlled by the reaction duration and catalyst concentration.

DISPERSION OF NANOCLAY IN 1,4-POLYBUTADIENE

ABSTRACT Two approaches to obtaining better dispersion of organo-modified nanoclay in high-molecular weight polybutadiene were assessed: (1) chemical modification of the polymer to increase its affinity for the silicate layers and (2) increasing the stretching component of the flow field used to mix the materials. As expected, the degree of dispersion, that is, the extent of intercalation of the polymer into the clay galleries and amount of exfoliation of the clay layers, increased with closer matching of the respective solubility parameters of the components. The efficiency of mechanical mixing was greater for flow fields dominated by stretching (extensional flow); less mix energy had to be expended to achieve a given level of reinforcement. However, without sufficient affinity of the polymer for the clay, complete exfoliation could not be obtained solely by mixing. Nevertheless, incomplete dispersion of the nanoclay still yields more than 40-fold increases in viscosity with 5% clay.

Molecular dynamics-based selectivity for Fast-Field-Cycling relaxometry by Overhauser and solid effect dynamic nuclear polarization

In the last decade nuclear spin hyperpolarization methods, especially Dynamic Nuclear Polarization (DNP), have provided unprecedented possibilities for various NMR techniques by increasing the sensitivity by several orders of magnitude. Recently, in-situ DNP-enhanced Fast Field Cycling (FFC) relaxometry was shown to provide appreciable NMR signal enhancements in liquids and viscous systems. In this work, a measurement protocol for DNP-enhanced NMR studies is introduced which enables the selective detection of nuclear spin hyperpolarized by either Overhauser effect or solid effect DNP. Based on field-cycled DNP and relaxation studies it is shown that these methods allow for the independent measurement of polymer and solvent nuclear spins in a concentrated solution of high molecular weight polybutadiene in benzene doped with α,γ-bisdiphenylene-β-phenylallyl radical. Appreciable NMR signal enhancements of about 10-fold were obtained for both constituents. Moreover, qualitative information about the dynamics of the radical and solvent was obtained. Selective DNP-enhanced FFC relaxometry is applied for the measurement of the 1H nuclear magnetic relaxation dispersion of both constituents with improved precision. The introduced method is expected to greatly facilitate NMR studies of complex systems with multiple overlapping signal contributions that cannot be distinguished by standard methods.

Single-chain polybutadiene organometallic nanoparticles: an experimental and theoretical study.

High molecular weight polybutadienes and rhodium complexes were used to produce single chain organometallic nanoparticles. Irradiation of high cis-polybutadiene in the presence of a photosensitizer isomerised the double bonds to produce differing cis/trans ratios within the polymer. Notably, a higher cis percentage of carbon-carbon double bonds within the polymer structure led to faster binding of metal ions, as well as their faster removal by competing phosphine ligands. The experimental results were supported and rationalized by DFT computations.

The component miscibility evolution during polymerization of the polybutadiene containing styrene solutions

In situ graft copolymerization of polystyrene (PS) on polybutadiene (PB) during polymerization of PB solution in styrene monomer was investigated to determine the performance of grafting process, chain structure of generated copolymers, and their effectiveness as compatibilizing agents for incompatible PS-rich and PB-rich phases. The amount of copolymers and their chain structures at different stages of polymerization were determined by gel permeation chromatography (GPC) curves of the reactive blends (taken directly from the reaction) and physical blends (physically prepared based on total composition of reactive blends). It was demonstrated that copolymer formation started from the early stage of polymerization and continued up to the phase inversion stage. In addition, PS grafting on PB occurred initially via single-chain attachment and then converted to a double-chain scenario later on. Compatibilizing efficiency of the copolymers was evaluated by Huggins coefficient (k H) obtained by performing dilute solution viscometry (DSV) on samples taken at different stages of conversions. The effect of molecular weight of PB on the grafting process and the effectiveness of copolymers generated were also studied. It was found that while compatibilizing role of the copolymers produced from high molecular weight PB (HPB) increases as conversion goes further, the compatibilizing efficiency of the copolymers produced from low molecular weight PB (LPB) shows a very sharp variation in a small range of conversion. Plotting k H of physical blends against weight fraction of PB molecules in solid content of the solutions (w PB) showed negative deviation from mixture law with a W-like pattern containing two minima with a maximum in between. While a negative deviation was assumed as indication of immiscibility of the components, upward deviation at middle values of w PB was attributed to molecular segregations that reduce the interface between the incompatible PS-rich and PB-rich phases.

Advanced rheological characterization of soft colloidal model systems

The complex flow behavior of polymer-based soft colloidal model systems was investigated using steady and oscillatory shear to prove new concepts for advanced rheological characterization. In the very dilute regime we investigated high molecular weight polybutadiene star polymers to quantify the internal relaxation time arising from the polymeric nature of these ultra-soft colloids. The observed shear-induced brush deformation is interpreted in terms of the internal Zimm time τz. The observed dependence of τz on matrix viscosity can be explained by shrinkage of the star polymer due to an increasing incompatibility with increasing matrix molecular weight. The influence of the polymeric nature on the characteristic structural relaxation time in the concentrated regime was investigated using non-linear rheology following Wyss et al (SRFS) (2007 Phys. Rev. Lett. 98 238303). Here we used star-like block copolymer micelles to systematically tune the ‘softness’ of the colloids by variation of the block ratio. A master curve with proper scaling parameters could be generated independent of the degree of colloidal ‘softness’. However, the obtained strain-rate independent structural relaxation time τ0 was not observed in the linear regime. In addition, a high frequency discrepancy was clearly found in all our experimental data. Both reflect the shortcomings of the SRFS approach.

Microstructural and property changes in high pressure treated carbon nanotube/polybutadiene composites

In a comprehensive investigation of carbon nanotube (CNT) filled liquid and solid polybutadienes of molecular weights 2600 and 100000, respectively, we report results of thermal conductivity (κ), glass transition temperature (Tg), interfacial interaction and microstructure before and after simultaneous high-pressure and high-temperature (HP&HT) treatment. The HP&HT treatment changed polybutadiene from a liquid or solid to a highly cross-linked, ebonite-like, state. Concurrently, the microstructure changed from randomly dispersed CNTs to a web-like structure of coated and/or wrapped CNTs, with a permanent shift in their D*-band by as much as ∼16 cm−1. Moreover, κ of the recovered state of a 2.9 wt% –COOH functionalized multi-wall carbon nanotube (MWCNT) composite increased by ∼34% predominantly due to an irreversible densification and a consequentially increased phonon velocity. Results prior to treatment show that single-wall carbon nanotube (SWCNT) fillers promote κ better (17%/wt%) than –SH functionalized MWCNT fillers (8%/wt%), which is accounted for by their higher aspect ratio, whereas their about twice as high κ appears to be unimportant. The SWCNTs also raise Tg slightly more than MWCNTs and, in particular, under the most densified conditions and for the high molecular weight polybutadiene, which may be due to more favorable conditions for coating/wrapping.

Phase Structure Changes in a Sheared Blend of High Molecular Weight Polybutadiene and Polyisoprene Elastomers

Abstract The flow-induced phase behavior of polyisoprene—polybutadiene elastomer blends is of concern to the rubber industry because of the wide practical applications of these blends. We have been investigating examples of these blends using a Rheo-SALS instrument in conjunction with light microscopy. The subject of this work was a high molecular weight, near-critical blend (35/65 ratio) comprising polybutadiene (Mn=413, 000) and polyisoprene (Mn=177, 000) (Blend II). The results were contrasted with those for a previously studied blend (Blend I) comprising polybutadiene (Mn=164, 000) and polyisoprene (Mn=125, 000), also near the critical composition at a 40/60 ratio. Both featured the same microstructure. Each was examined under quiescence and flow conditions. For Blend I at a 24 °C quench depth, the scattering pattern was the expected spinodal ring; which, upon shearing, changed to an H-shaped pattern and then to a bright streak in the vorticity direction. Direct observation showed that these patterns corresponded to a fibrillar structure aligned in the flow direction. Similar light scattering patterns were obtained after a temperature jump (24 °C) under steady-state shearing. With Blend II at a 40 °C quench depth, the scattering pattern was again a spinodal ring, but this changed on shearing to an anisotropic pattern having the shape of an “8” or a “butterfly.” The shape of this pattern depended on shear rate, and its origin was hypothesized to be phase domains following helical paths with axes aligned in the vorticity direction. The corresponding micrographs are consistent with this supposition, as is an instability phenomena observed in the parallel-plate rheometer at higher shear rates. These purely hydrodynamic phenomena should be kept in mind when interpreting observations of “flow-induced mixing” at lower quench depths.

The gel point as reference state: A simple kinetic model for crosslinking polybutadiene via hydrosilation

Abstract Kinetic data can be described in a simple model when using the gel point as reference state. This has been shown for crosslinking data on five high molecular weight polybutadienes (18 100–97 000 g/mol). Experiments were carried out under isothermal conditions with a constant amount of catalyst. Crosslinking took place by a hydrosilation reaction at vinyl sites which were randomly distributed along the backbone of the polybutadiene precursor molecules using the bifunctional aromatic silane p-bis(dimethylsilyl) benzene as connector. FTIR measurements showed that the hydrosilation reaction followed first order kinetics. The critical gel time, tc, was determined by the instant at which power law relaxation behavior was observed (i.e. tan δ = constant) over the two lowest decades in frequency. The main parameters that were observed to affect tc were the stoichiometric ratio, r, and the functionality of the polybutadiene, f. It was observed that the time to reach the gel point decreased with increasing precursor molecular weight (~f) of the polybutadiene. The gel time also decreased when increasing the initial amount of silane crosslinker. We were able to find a relationship between the gel time measured by the CFS technique and r and f by coupling the Flory-Stockmayer gelation theory with a simple first order kinetic curing scheme.

On the nature of static interactions between surfaces separated by a polymer solution

Abstract Experiments with a surface force apparatus have been performed on static interactions between solid surfaces separated by solutions of high molecular weight polybutadiene. Static forces have been defined at the end of the dynamic component relaxation created by the sphere displacement. Measurements of interaction forces have been performed both as a function of solution concentration and surface separation. Concentration has been varied from the dilute to the semi-dilute regime. Two distinct types of behaviour were observed when the concentration was varied. Below C ∗ , the threshold of the semi-dilute regime, the structure of the adsorbed layers was found to be mainly responsible for the force variations. Above C ∗ , a depletion of free chains at the surface of the adsorbed layers will contribute to the measured attraction. These experiments are closely related to stabilisation and destabilisation by depletion, phenomena which are observed in suspensions.

Onset of excluded-volume effects in chain dynamics

The infinite-dilution oscillatory flow birefringence properties of five high molecular weight polybutadienes (M=3.55×10 5 , 9.25×10 6 , 2.95×10 6 , 3.14×10 6 , and 1.6×10 7 ) have been determined in dioctyl phthalate at 18.0, 21.5, 25.0, and 30.0°C. The θ temperature for this system has been estimated as 21.5°C, and thus the results extend from the θ into the marginal solvent regime. At the highest temperature, the onset of excluded-volume effects is clearly evident. The data are interpreted in terms of the bead-spring model incorporating five distinct approaches to treating excluded-volume interactions

Spectroscopic studies of an ambient-pressure process for the selective hydrogenation of polybutadienes

The effectiveness of a low-pressure hydrogenation process for the selective hydrogenation of the vinyl-1,2, cis-1,4 and trans-1,4 structural units in high molecular weight polybutadienes was explored. The NMR, FTIR and Raman results indicate that it is possible to monitor the hydrogenation process by analysis of partially hydrogenated polybutadienes. NMR data made it possible to see the incorporation of an aromatic impurity in the polymer. The first report is made of the use of Raman spectroscopy for analyzing the hydrogenation of a polydiene.

Effects of concentration and thermodynamic interaction on the viscoelastic properties of polymer solutions

Linear viscoelastic measurements are reported for solutions of a high molecular weight polybutadiene covering the entire range of concentration from pure polymer to pure solvent at 25°C in a nearly θ solvent (dioctyl phtalate) and a good solvent (phenyloctane). Three regimes of concentration are found for the viscosity in each solvent. Elastic response is also identical for the two solvents, with G° N (inferred from G″ m ) ∞1/J° e ∞φ 2.3 for φ>0.02. The results in semidilute solution compare favorably with the predictions of a recent two-parameter scaling theory

Nuclear magnetic resonance and temporary elasticity in molten polybutadiene: Concentration, chain length, and microstructure dependences

This work deals with effects of variations of chain length and polymer concentration observed upon the gel-like behavior of high molecular weight polybutadiene. The relaxation rate σ of the transverse magnetization of protons attached to polymer chains was found to be governed by the residual dipole–dipole interaction of nuclear spins, a pseudosolid mechanism already observed in several concentrated polymer solutions. The rate σ corresponding to a given microstructure was measured at room temperature; it was found to be a function of both the chain molecular weight M̄w and the polymer volume fraction φ, according to the formula σ−1(φ,M̄w)=φ−1[1+2400(1−0.85φ) (M̄w)−1/2]σ−1∞, which applies within the ranges of 0.5×105<M̄w<5.45×105 g mole−1 and 0.4<φ<1.0. Here σ−1∞ corresponds to infinite chain length. The microstructure of pure polybutadiene chains was varied by keeping a constant length (M̄w=2×105 g mole−1). Measurements were performed at several constant temperature intervals above the glass transition. The isofree volume relaxation time σ−1f was found to be a linear function of the inverse of the values of the modulus of temporary elasticity G0N, which are reported in the literature for similar microstructures. It is suggested to associate the network structure perceived from NMR to the transient network responsible for the temporary elasticity of polybutadiene.

Extensional stresses during polymer flow in ducts

During the flow of high molecular weight, narrow-, and broad-distribution polybutadienes and polyisoprenes rheo-optical measurements were conducted of extensional stresses acting along the flow axis in the preentrance and entrance regions of the duct and of their subsequent relaxation in the duct. The extensional stresses increase in the preentrance region, reach their maximum values at a distance of two or three tenths of the duct width from its edges, and then relax. The position of the maximum extensional stress is independent of polymer characteristics, shear stresses in the duct, and shape of the entrance and dimensions of the rectangular duct. The dependence of the maximum extensional stress on the shear stress of the duct wall can be assumed to be linear for small values. The length of the stress relaxation zone depends on the shear stress at the duct wall and the molecular mass distribution. It is independent of the molecular masses in narrow-distribution polymers. For the polymers investigated, a generalized dependence was obtained for the reduced duct length over which the extensional stresses relax to zero from the reduced deformation rate. This dependence takes into account the characteristic polymer relaxation times and the value of the molecular mass of the chain between the fluctuation entanglement. A considerable decrease in the duct's length-to-width ratio leads to an increase in the maximum values of the extensional stresses. A decreases in the duct entrance angle causes a reduction in the rate of increase of extensional stresses, the maximum values, and the acceleration of the relaxation processes in the duct. A decrease in the ratio of the width of the preentrance region to the duct width leads to a reduction in the maximum in extensional stresses. It is shown that one of the causes for the instability of the polymer flow in the ducts can be the rupture of polymers due to their extension in the preentrance and entrance regions. Calculations were done that describe satisfactorily the relationship between the values of the maximum extensional stresses and the shear rate and stresses on the duct wall.

Anionic polymerization. III. Polymerization of butadiene with alkali metal alkoxide‐modified alkali metal system

AbstractA high molecular weight polybutadiene was prepared in hexane solvent by using alkali metal (Li, Na, K) and metal tert‐butoxide (Li, Na, K) as a polymerization initiator. The microstructure of polybutadiene varies, depending on the type of modifiers and polymerization and temperatures. The results and mechanistic implications of this study are discussed.

Polarization‐optical investigation of normal and shear stresses in flow of polymers

AbstractA method has been suggested for calculating the first difference of normal stresses characterizing the flow of polymers at high shear stresses. The calculations are based on the results of rheooptical measurements in a slit of rectangular cross section. It has been found, for several samples of high molecular weight polybutadienes and polyisoprenes, that the flow behavior of the representatives of the given polymer homologous series having different molecular weights is characterized by a general relationship between the first normal stress differences and the shear stresses in those cases where the polymers are characterized by narrow molecular weight distributions. It has also been established that the first normal stress difference sharply increases in the region of shear stresses which immediately precedes the spurt—a jumpwise increase of the flow rate at a certain critical value of shear stress; while for polymers of wide molecular weight distribution the increase of the normal stress difference in the region of high values of shear stresses is retarded. Equilibrium swell of the extrudate has been measured and the first normal stress difference determined by the rheo‐optical method has been found to agree satisfactorily with the values calculated from the swelling ratios according to theoretical models.

Use of gel‐permeation chromatography in the determination of the composition of two‐polymer mixtures

AbstractThe possibility of evaluating with acceptable accuracy the composition of a two‐polymer mixture which is well separated by GPC, was studied by using mixtures of high molecular weight polybutadiene (M̄w = 4.5 × 105) and low molecular weight polyiso‐butylene (M̄n in the range of 103). It was concluded that a satisfactory evaluation of the composition of a polymer mixture can be achieved, provided that the variations of the refractive index with the molecular weight are taken into account for the low molecular weight polymer (the polyisobutylene).