Linear Polybutadiene Research Articles

Surface Nanopatterning Using the Self-Assembly of Linear Polymers on Surfaces after Solvent Evaporation

The morphology of linear polybutadiene physisorbed on freshly cleaved mica from a dilute polymer solution is investigated through atomic force microscopy. A fine-structure study shows that the monolayer morphology in air (after rapid solvent evaporation) depends strongly on the molecular weight (Mw) of the linear polymer, the adsorbed amount, and the conformation adopted by the adsorbed polymer chains under good solvent conditions. The dependence of the observed polymer structure on Mw is most significant for samples with high surface density, where the intermolecular interactions among the adsorbed polymers are important. For high surface density, the adsorbed polymers tend to aggregate and minimize unfavorable contacts with air for all of the different Mw samples, leading to an isotropic structural pattern. These structural phenomena with increasing surface density are explained on the basis of the intermolecular interactions of the adsorbed polymers under good solvent conditions, and after the abrupt solvent evaporation corresponding to poor solvent conditions. The experimental observations are further discussed using the results obtained from molecular dynamics simulations of a simple coarse-grained model.

Synthesis and properties of thermoplastic polyethylene based polyurethanes (PE-PUs)

Polyethylene based polyurethanes (PE-PUs) with 20% ethyl branches were synthesized through hydrogenation reaction of linear and thermoplastic hydroxyl-terminated polybutadiene based polyurethanes (HTPB-PUs), which has not been explored widely. Linear and thermoplastic HTPB-PUs with M w ranged from 130~280 kg/mol were synthesized by microwave-assisted reaction. More importantly, we systematically researched a series of reaction conditions to ensure the degree of hydrogenation meanwhile slow down the extent of degradation reaction of urethane bond. In addition, structure and thermal performance of PE-PUs have been investigated in the present work by NMR, FT-IR, DSC and TGA. The M w of PE-PUs ranging from 120~207 kg/mol were carried out with a high temperature GPC. Moreover, the degree of crystalline of PE-PUs with 20% ethyl branches at the range of 10% to 33% were further explored by X-ray diffraction, which in turn certify that the PE-PUs possess certain strength but lower than polyethylene with no branches.

Normal-phase (temperature gradient) interaction chromatography – A powerful tool for the characterisation of high molecular weight chain-end functionalised polymers

We report here, for the first time, quantitative analysis of end-group functionalisation and the extent of end-group modification of polymers with molar mass up to 200,000gmol−1, using a combination of isothermal and temperature gradient interaction chromatography. At such high molecular weights, other common analytical techniques such as MALDI-ToF-MS and NMR spectroscopy are simply unable to offer any quantitative insight into the end-group functionality of polymers. Thus, normal phase isothermal interaction chromatography (NP-IIC) has been used to characterise a series of polystyrene samples, with identical molar mass (c. 90,000gmol−1), each carrying a single chain-end functionality of varying polarity, introduced via a series of end-group transformation reactions – from silyl-protected alcohol→primary alcohol→alkyl bromide. It is shown that the polarity of the functional group dictates the elution volume of the polymers and that NP-IIC could be used to monitor the quantitative end-group transformation. Thus, rather than estimating the success of the transformation reaction from the very small peaks observed in 1H NMR spectra, NP-IIC gives clear chromatographic peaks, whose retention volumes change dramatically only as a consequence of each new chain-end functional group. We also describe the analysis, by a combination of normal phase isothermal and temperature gradient interaction chromatography, of a series of linear polybutadiene samples of varying molar mass (28,000–200,000gmol−1) each carrying a single primary alcohol functionality at the chain-end. The primary alcohol functionality enabled the separation of functionalised and non-functionalised polymers, which eluted at different retention volumes despite identical molecular weights. It is all the more remarkable that complete (baseline) resolution can be achieved for two polymers with an identical molar mass (<200,000gmol−1), which differ only in that one sample is functionalised with a single primary alcohol group.

Field-Cycling NMR Relaxometry Probing the Microscopic Dynamics in Polymer Melts

Field-cycling (FC) 1H and 2H NMR relaxometry is applied to linear polybutadiene (PB) of different molar mass (M) in order to test current polymer theories. Applying earth field compensation, five decades in the frequency dependence of the spin–lattice relaxation rate T1–1(ν) = R1(ν) are accessed (200 Hz - 30 MHz), and we focus on the crossover from Rouse to entanglement dynamics. A refined evaluation is presented, which avoids application of frequency–temperature superposition as well as Fourier transformation. Instead, the power-law exponent e in the entanglement regime is directly determined from the susceptibility representation χNMR″(ω) = ω/T1(ω) ∝ ωe by a derivative method. Correspondingly, a power-law t–e characterizes the decay in the time domain, i.e., the dipolar correlation function. For the total 1H relaxation, comprising intra- and intermolecular relaxation, a high-M exponent etotal = 0.31 ± 0.03 is found. An isotope dilution experiment, which yields the intramolecular relaxation reflecting so...

Preparation of Hydroxyl-Terminated Polybutadiene with High Cis-1,4 Content

Hydroxyl-terminated polybutadiene (HTPB) with high cis-1,4 content (>95.0%) has been prepared via a two-step method by taking commercial butadiene rubber (BR9000) as a starting material, including the one-pot synthesis of aldehyde-group-terminated polybutadiene (ATPB) in high efficiency and the subsequent reduction reaction. The double bonds distributed in linear polybutadiene were first epoxidized and then cleaved at the exact epoxidized sites. The epoxidation reaction by 3-chloroperbenzoic acid and chain-cleavage reaction by periodic acid are controllable, highly efficient, selective, and quantitative. Along with an epoxy percent increase, the molecular weight of ATPB prepared via a one-pot method decreased with a relatively narrow polydispersity index. The aldehyde groups in the chain ends were reduced by NaBH4 to produce HTPB, in which the high cis-1,4 content of BR was retained.

Synthesis and polymerization of cyclobutenyl-functionalized polylactide and polycaprolactone: a consecutive ROP/ROMP route towards poly(1,4-butadiene)-g-polyesters

Efficient preparation of cyclobutenyl end-functionalized polyester macromonomers bearing polylactide (PLA) or poly(ε-caprolactone) (PCL) arms was achieved by organocatalyzed ring-opening polymerization (ROP) of L-lactide or ε-caprolactone in the presence of cis-3,4-bis(hydroxymethyl)cyclobutene or cis-4-benzyloxymethyl-3-hydroxymethylcyclobutene acting as an initiator. Cyclobutenyl end-functionalized PLA and PCL macromonomers having one or two arms were obtained in high yields with excellent control over molecular weights (up to 11 000 g mol−1) and dispersity (PDI < 1.25) by organocatalyzed ROP using 4-(N,N-dimethylamino)pyridine (DMAP) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), respectively. Ring-opening metathesis polymerization (ROMP) of the macromonomers using ruthenium-based Grubbs' second generation catalyst afforded well-defined polybutadiene-g-polyester copolymers having an exclusively linear polybutadiene backbone with a strictly 1,4-type microstructure, with molecular weights ranging from 20 000 to 170 000 g mol−1 and low dispersities (PDI ≤ 1.30). The products resulting from this consecutive ROP/ROMP route represent the first examples of poly(1,4-butadiene)-g-polyesters through the macromonomer route.

Dynamics of Linear Polybutadienes in Solution Studied by Field Cycling 1H NMR.

Field cycling 1H NMR relaxometry is utilized to investigate dynamics in solutions of monodisperse polybutadienes of different molecular mass (M) and deuterated toluene. Broad temperature and polymer mass fraction ranges (c = 5-100%) are studied. By applying frequency-temperature superposition, susceptibility master curves χ″DD(ωτs) are constructed. They cover the segmental relaxation and polymer chain dynamics, and provide the concentration dependence of the segmental time constant τs(T). The relaxation strength of polymer dynamics is reduced similarly for all M with decreasing c; for the lowest c, almost no polymer dynamics shows up, that is, the dipolar correlation function obtained via Fourier transform decays almost completely due to segmental dynamics. The dipolar correlation function is decomposed into contributions of segmental and polymer dynamics. Its long-time power-law exponent associated with entanglement dynamics is increased from its bulk value with reduced c. This is interpreted as a continuous increase of the effective entanglement molecular mass.

Universal Polymer Dynamics Revealed by Field Cycling 1H NMR

We apply fast field cycling 1H NMR to study segmental reorientation dynamics in melts of linear polybutadiene, polyisoprene, and polydimethylsiloxane in the high molecular weight limit. Measuring fully protonated as well as partially deuterated polymers, we show that in contrast to previous reports the relaxation behavior at low frequencies, for which polymer-specific contributions show up, is not universal but depends on the particular internuclear vectors of the 1H spin pairs in the monomer unit. Only after extracting the polymer specific contributions from the overall susceptibility spectra by accounting for the glassy contribution, the “polymer spectra” reveal universal behavior which can be described by two power law regimes: one attributed to free Rouse dynamics and one, at lower frequencies, to entanglement effects. Yet the predictions of the tube-reptation model are not observed.

Wall slip and spurt flow of polybutadiene

Spurt occurs in the flow of entangled melts in a capillary rheometer in which the driving pressure is controlled. As the driving pressure increases, at a critical value there is a sudden increase in flow rate, often called spurt. This discontinuity is followed by another regime of smoothly increasing flow rate. A phenomenon that may contribute to this instability is a curve of wall shear stress versus slip velocity that has a maximum followed by a minimum, and there are models that predict such behavior. We used a sliding plate rheometer (SPR) to study wall slip for a highly entangled, linear polybutadiene at 1atm and at 46MPa. By varying the plate speed, we were able to explore the entire curve of shear stress versus slip velocity. This curve exhibited a maximum and a minimum in the stress, providing support for theories predicting this behavior and an explanation for the spurt effect in capillary rheometry. The spurt flow of the same polymer was also observed, and slip velocities were estimated and compared with those determined using the SPR. The slip velocities obtained using the two instruments were in good agreement.

Direct Rheological Evidence of Monomer Density Reequilibration for Entangled Polymer Melts

The monomer density reequilibration relaxation is directly observed for the first time from the linear viscoelastic data of very high molecular weight linear polybutadiene, polyisobutene and polyisoprene. We use a simple procedure of subtracting contributions of the high-frequency Rouse-like modes from the curves. The stress decay of the monomer redistribution process is characterized by a single exponential (Maxwell form), and the observed relaxation strength is one-fourth of the plateau modulus. Moreover, the characteristic relaxation time is close to the equilibration time tau(e) of an entanglement segment. The observed reequilibration dynamics appears to be independent of polymer species. The high-frequency relaxation modes can be reconstructed as a superposition of power law Rouse-like dynamics and Maxwell monomer reequilibration. The dynamic moduli curves calculated in this way show excellent agreement with the results in the high-frequency region. We further propose a possible experimental definition for tau(e). It corresponds to an easily observable cross-point between the extended plateau modulus and the power law region of the loss modulus.

Viscoelastic behavior of fullerene end-capped linear polymers

Viscoelastic behavior of C 60-end-capped linear polybutadiene and C 60-end-capped poly(butadiene- co-styrene) with molecular weight ( M n) ranging from 30 to 130 kg/mol and with polydispersity index ( M w/ M n) ranging from 1.02 to 1.08 was investigated. These polymers were synthesized through anionic polymerization of butadiene and styrene in hexane, in which the living ends were capped with the C 60 via an alcoholate bridging. Rheological measurements showed that the polymer dynamics in the terminal zone were profoundly affected by the presence of fullerene, while the dynamics in the entanglement-plateau and at the terminal relaxation were nearly unaffected.

Unified application of the coupling model to segmental, Rouse, and terminal dynamics of entangled polymers

The temperature dependence and relaxation function breadth of segmental dynamics ( α-relaxation) for 1,2-polybutadiene and 1,4-polybutadiene are used to predict their respective temperature-dependent terminal relaxation times by unified application of the Ngai coupling model. Literature results for the terminal flow of near-monodisperse linear polybutadienes having widely varying molecular weights are successfully represented using the coupling model by variation of only a single parameter, C, which is the proportionality constant between the longest Rouse relaxation time and the primitive relaxation time which underlies the cooperative segmental process. The value of C varies with molecular weight ( M) according to C ∝ M b where b is found to range from 1.8 to 2.1, in close agreement with the expected exponent of 2. Contrary to experimental data and coupling model predictions, reptation theory predicts identical influences of temperature on Rouse and terminal relaxation processes; we suggest that invoking a temperature dependence for contour length fluctuations, and hence number of effective entanglements per chain, may resolve this deficiency of the tube model.

Development of a Kinetic Model for Thermal Crosslinking of Rubbery Polymers

AbstractSummary: A kinetic model for the thermal crosslinking of rubbery polymers is presented. The reaction mechanism used to develop the model includes thermal radical generation producing a polymeric radical and a primary radical, crosslinking from attack of a polymer radical to any inactive polymer molecule, bimolecular radical termination among chains of any degree of branching, and radical termination between a polymer radical and a primary radical from the thermal radical generation. The overall polymer population is divided into “generations”, which are defined in terms of the number of primary (linear) chains of original rubbery polymer attached to the polymer molecule. Mass balances for each generation are written down, and expressions to calculate fraction of branched molecules, gel fraction, and number and weight average chain lengths are derived. Model simulations, parameter sensitivity analyses and preliminary parameter estimation studies are presented, taking the thermal crosslinking of linear polybutadiene as a case study.Development of a kinetic model for thermal crosslinking of rubbery polymers: reaction mechanism, model equations and parameter sensitivity analyses.magnified imageDevelopment of a kinetic model for thermal crosslinking of rubbery polymers: reaction mechanism, model equations and parameter sensitivity analyses.

Formation and Development of Phase Morphology and Structure on Polystyrene Blends. II. Study of Phase Behavior and Structure Character of PS/PS‐g‐MAH/LEPB/PcBR Semimiscible System During Melt Blending by Scanning Electron Microscopy

In this paper, polystyrene (PS)/poly(cis‐butadiene) rubber (PcBR) blends were prepared by melt blending. Polystyrene‐graft‐maleic anhydride (PS‐g‐MAH) and linear epoxy polybutadiene (LEPB) were added to the blends to increase the compatibility. The blends were shown to be semimiscible by small‐angle X‐ray scattering (SAXS). The morphology of the blends was examined by partial extraction of material. The form and the distribution of the phases were studied by scanning electron microscopy (SEM). The mixing process of the blends was characterized through the characteristic length, L, and the average characteristic length, L m . The distribution of the characteristic length, L, was shown to be consistent with the log normal Gaussian distribution. The mixing system was shown to possess self‐similarity in a certain range of time, as shown through a scale function. Furthermore, the fractal dimension, D, was calculated at different times and shown to be a parameter that can be used to describe the process of melt blending. The PS‐g‐MAH and LEPB were shown to increase the compatibility by comparison with the immiscible blend PS/PcBR.

Coupling Model Interpretation of Thermorheological Complexity in Polybutadienes with Varied Microstructure

Small-amplitude oscillatory shear rheology was used to investigate relaxation dynamics for two linear polybutadienes with low-vinyl (7% 1,2-addition; PBd-L) and high-vinyl (94% 1,2-addition; PBd-H) microstructures. The Mw values were equal to 38.7 and 80.1 kg/mol for PBd-L and PBd-H, respectively, and both polymers were near-monodisperse (Mw/Mn < 1.05). These molecular weights were selected in order to keep the number of entanglements per chain, and hence the plateau length, fairly equivalent for these two polymers. Well-defined terminal flow and segmental relaxation (α-relaxation) loss modulus peaks in the isothermal linear viscoelastic data were used to determine relaxation times, thus the necessity of time−temperature superposition was avoided. These results are interpreted in the context of the Ngai coupling model (CM). We apply the model to both relaxation processes in a unified approach by adopting the CM framework which contends that the primitive relaxation which underlies the cooperative α-relaxa...

Polystyrene Nanoparticles with Anionically Polymerized Polybutadiene Brushes

Model hairy nanoparticles of highly cross-linked polystyrene (PS) cores and linear polybutadiene (PBd) brushes were synthesized. The PS cores were obtained using conventional microemulsion polymerization. The linear PBd brushes were synthesized using surface initiated living anionic polymerization. The PS core nanoparticles of 44 ± 12 nm in diameter (volume weight average) were first lithinated using a combination of butyllithium and N,N,N‘,N‘-tetramethylethylenediamine. Butadiene was subsequently polymerized at the surface of the particles. Two series of samples were synthesized with different degrees of polymerization (N) and grafting densities (σ). In the first series, while σ was constant at ∼0.14 chains/nm2 (∼500 chains per particle), N changed from 37, 74, 139, to 198. Accordingly, the Mw of brushes changed from 2.0, 4.0, 7.5, to 10.7 kg/mol. In the second series, the weight ratio between PS and PBd was fixed at PS/PBd ≅ 5/2 (σN was constant in this case) and σ varied from 0.15 to 0.08 chains/nm2 an...

Nanoscale Cooperative Length of Local Segmental Motion in Polybutadiene

The influence of molecular weight between cross-links, Mc, on the segmental α-relaxation of polybutadiene (PBd) networks was probed using dynamic mechanical spectroscopy. Linear polybutadiene (Mw =...

Experimental characterization of extrudate swell behavior of linear polybutadiene

This paper describes an experimental study of the time-dependent extrudate swell behavior of a series of linear polybutadienes as a function of molecular weight (MW) and molecular weight distribution (MWD). The “initial” extrudate swell, i.e., the extrudate swell measured near the die exit, is universally found to be around 1.10, independent of MW, MWD and the extrusion rate. Like the initial extrudate swell, the extrudate surface velocity at the die exit, Vs, when normalized by the average capillary flow velocity, Vp, is also a relatively universal function of the distance X from the exit plane. It increases from 0.3 to 1 over a normalized distance from X/D=0 to X/D=0.035 regardless of MW, MWD, and the extrusion rate. In the presence of exit slip, which can be produced by coating the exit wall with a fluoropolymer, Vs is nearly equal to Vp even at x=0. The extrudate swell at a given distance from the exit is shown to be independent of the molecular weight for monodisperse samples. A small tail in the MWD at the high end produces considerably larger extrudate swell. Although the extrudate swell increases with increasing applied stress for a given sample, a series of polymer solutions of different concentrations show that the real controlling variable is the applied stress normalized by the material’s elastic plateau modulus. The extrudate swell is also found to depend systematically on the die diameter at all stages of its growth. Moreover, the extrudate swell is greater when it is allowed to grow in media (other than the air) such as oil and water. These two last effects can be understood in terms of the free-surface-to-volume ratio of the extrudate: the larger this ratio is more rapidly the residual molecular deformation in the extrudate can relax. A proper understanding of these interfacial effects will have important implications in processes such as injection/blow molding and film blowing from the viewpoints of both industrial practice and numerical simulations.

Nonuniversal Behavior of the Thermodynamic Interaction Parameter in Blends of Star and Linear Polybutadiene

Values of the bulk thermodynamic interaction parameter, χ eff , for blends of anionically polymerized star (number of arms = 4, 6, 8, 12) and linear polybutadienes (PB) of well-defined architecture and molecular weight were measured as a function of temperature using small-angle neutron scattering. Comparison of these measured values of χ eff -with results from comparable polystyrene (PS) blends suggests the existence of nonuniversal aspects in the thermodynamic interaction due to entropic contributions, χ e , arising from architectural differences in chains. While the value of χ e , for PS star/linear blends increases monotonically with number of arms in the star, the value of χ e in the PB star/linear blends does not, a result which cannot be anticipated by the Gaussian field theory (GFT) of Fredrickson et al. 1 An important discrepancy between theory and experiment is also found for the variation of χ e , with linear chain length. Theory anticipates the value of χ e , should decrease with increasing linear chain size, but in fact it increases. Qualitative agreement with the GFT is found on two counts: χ e , decreases with increasing concentration of star (when assuming χ isotpic for linear/linear blends is constant with concentration), and χ e decreases with increasing length of the star arm. In general, the value of χ e for a PB blend of star and linear components is larger than the value of χ e for a comparable PS blend. Indeed, phase separation is observed in one particular PB blend of a six-arm star with a sufficiently large linear chain.

Polyurethane elastomers made from linear polybutadiene diols

Segmented polyurethane elastomers made from linear polybutadiene diols terminated with primary (Krasol LBH-P) or secondary (Krasol LBH) hydroxy groups, alicyclic diisocyanate, and aliphatic chain extender were prepared and tested. The system was chemically crosslinked either through isocyanurate, that is, hexahydro-1,3,5-triazine-2,4,6-trione groups (formed by catalyzed cyclotrimerization of isocyanate groups), or by low molecular weight triols. The best balance of stress-strain properties and reasonable thermal stability was obtained for systems in which only a small amount of chemical crosslinks was present in predominantly physically crosslinked networks. The influence of the type of polymer diol, chemical crosslinking, diisocyanate, and technique of preparation on mechanical, thermal, and swelling properties is discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 84–91, 2002