Polybutadiene Networks Research Articles

Elastomer Composites with High Damping and Low Thermal Resistance via Hierarchical Interactions and Regulating Filler.

Modern microelectronics and emerging technologies such as wearable electronics and soft robotics require elastomers to integrate high damping with low thermal resistance to avoid damage caused by vibrations and heat accumulation. However, the strong coupling between storage modulus and loss factor makes it generally challenging to simultaneously increase both thermal conductance and damping. Here, a strategy of introducing hierarchical interaction and regulating fillers in polybutadiene/spherical aluminum elastomer composites is reported to simultaneously achieve extraordinary damping ability of tan δ>1.0 and low thermal resistance of 0.15cm2 KW-1 , which surpasses state-of-the-art elastomers and their composites. The enhanced damping is attributed to increased energy dissipation via introducing the hierarchical hydrogen bond interactions in polybutadiene networks and the addition of spherical aluminum, which also functions as a thermally conductive filler to achieve low thermal resistance. As a proof of concept, the polybutadiene/spherical aluminum elastomer composites are used as thermal interface materials, showing effective heat dissipation for electronic devices in vibration scenarios. The combination of outstanding damping performance and extraordinary heat dissipation ability of the elastomer composites may create new opportunities for their applications in electronics.

DSC investigation of chain cooperativity rearrangements and critical length scale of polybutadiene networks in glass transition range

DSC investigation of chain cooperativity rearrangements and critical length scale of polybutadiene networks in glass transition range

Toughened epoxy‐liquid polybutadiene networks cured with anhydride with outstanding thermal and mechanical properties

AbstractToughened epoxy systems cured with anhydride‐based hardener were successfully prepared by incorporating nonpolar liquid polybutadiene (PB) previously functionalized with isocyanate groups (PBNCO). The NCO groups in PBNCO react with the hydroxyl and/or epoxy groups of the matrix forming a ER‐PB‐ER triblock copolymer. The block copolymer is evidenced by transmission electron microscopy (TEM). In fact the modified epoxy resin (ER) networks presented domains with cocontinuous‐like morphology, composed by PB and ER phases in nanomeric dimensions. The effect of PBNCO on the curing process of ER was studied by rheometry. Also the resulting networks were characterized by mechanical and dynamic mechanical properties, differential scanning calorimetry, and TEM. By adding an amount of rubber as high as 20 phr, a great improvement of toughness (around 140%) and impact resistance as well as a good transparency were achieved without significantly affecting the modulus and stiffness. Also the glass transition temperature (Tg) increased around 10°C with the presence of 5 phr of PBNCO. Even with the addition of 20 phr of rubber, the Tg of the system was superior than that found for the neat epoxy network. The outstanding physic‐mechanical performance is attributed to the peculiar morphology.

Recyclable, Self-Healing, Thermadapt Triple-Shape Memory Polymers Based on Dual Dynamic Bonds

Fabricating a single polymer network with a combination of multi-shape memory effect (multiple-SME), solid-state plasticity, recyclability and self-healing behavior remains challenges. We designed imine bonds and ionic hydrogen bonds dual crosslinked polybutadiene (PB) networks. The resultant PB networks showed triple-shape memory effect (triple-SME), where imine bonds could be used to fix the permanent shape and ionic hydrogen bonds and glass transition acted as the transition segments for fixing/releasing the temporary shapes. Additionally, the dual dynamic bonds offered PB networks outstanding solid-state plasticity, recyclability and self-healing behavior. This strategy provides some insights for preparing shape memory polymers integrating multiple-SME and multi-functionality.

Depolymerization of Cross-Linked Polybutadiene Networks in Situ Using Latent Alkene Metathesis

We report a novel approach whereby cross-linked polybutadiene (PB) networks can be depolymerized in situ based on thermally activated alkene metathesis. A commercially available latent Ru catalyst,...

Recyclable polymer networks containing hydroxyurethane dynamic cross-links: Tuning morphology, cross-link density, and associated properties with chain extenders

Conventional polymer networks are incapable of being reprocessed or recycled in the melt state, leading to sustainability and economic losses associated with spent polymer networks. With the incorporation of hydroxyurethane dynamic cross-links resulting from reaction of tricyclocarbonate and telechelic amine-terminated polymer, polybutadiene (PB) networks and poly(tetramethylene oxide) (PTMO) networks are reprocessable with full property recovery after multiple molding steps. Two types of small-molecule chain extender are incorporated into these networks to tune their morphologies, cross-link densities and associated properties. Addition of m-xylylenediamine (XYL) chain extender to PTMO networks increases the hard-segment content and leads to nanophase separation, which is absent when XYL is not present, and the elimination of cold crystallization behavior that is observed in PTMO networks without XYL. Addition of XYL also increases the cross-link density and rubbery plateau modulus of both PB and PTMO networks, and the resulting materials remain fully reprocessable. In contrast, addition of divinylbenzene dicyclocarbonate (DVBDC) chain extender enhances the cold crystallization behavior of molded PTMO-based networks and their crystallinity. Addition of DVBDC reduces the cross-link density and rubbery plateau modulus of both PB and PTMO networks, and the resulting networks exhibit selective property losses after reprocessing. This study demonstrates the simple and effective use of chain extenders in achieving tunability of dynamic network properties to satisfy requirements in different potential applications. It also provides a better understanding of structure-property relationships in dynamic covalent networks from both chemical and physical standpoints.

Azide and Alkyne Terminated Polybutadiene Binders: Synthesis, Cross-linking, and Propellant Studies

In composite solid propellants, the fuel and oxidizer are held together by a polymer binder. Among the different types of polymeric binders used in solid propellants, hydroxyl terminated polybutadiene (HTPB) is considered as the most versatile. HTPB is conventionally cured using isocyanates to form polyurethanes. However, the incompatibility of isocyanates with energetic oxidizers such as ammonium dinitramide and hydrazinium nitroformate, the short “pot life” of the propellant slurry, and undesirable side reactions with moisture are limiting factors which adversely affect the mechanical properties of HTPB based propellant. With an aim of resolving these problems, HTPB was chemically transformed to azidoethoxy carbonyl amine terminated polybutadiene and propargyloxy carbonyl amine terminated polybutadiene by adopting appropriate synthesis strategies and characterizing them by spectroscopic and chromatographic techniques. This is the first report on 1,3-dipolar addition reaction involving azide and alkyne end groups for cross-linking HTPB. The blend of these two polymers underwent curing under mild temperature (60 °C) conditions through 1,3-dipolar cycloaddition reaction resulting in triazole–triazoline networks. The curing parameters were studied using differential scanning calorimetry. The kinetic parameter, viz., activation energy, was computed to be 107.6 kJ/mol, the preexponential factor was 2.79 × 1012 s–1, and the rate constant at 60 °C was computed to be 3.64 × 10–5 s–1.The cure profile at a given temperature was predicted using the kinetic parameters. Rheological studies revealed that the gel time for curing through the 1,3-dipolar addition is 280 min compared to 120 min for curing through the urethane route. The mechanical properties of the resultant cured polybutadiene network were superior to those of polyurethanes. The cured triazoline–triazole polymer network exhibited biphasic morphology with two glass transitions (Tg) at −56 and 42 °C in contrast to the polyurethane which exhibited a single transition at −60 °C. This was corroborated by associated morphological changes observed by scanning probe microscopy. The propellant processed using this binder has the advantages of improved pot life as indicated by the end of the mix viscosity which is 165 Pa·s as compared with 352 Pa·s for the polyurethane system along with a slow build-up rate. The mechanical properties of the propellant are superior to polyurethane with an improvement of 14% in tensile strength, 22% enhancement in elongation at break, and 12% in modulus.

Investigation of Anisotropic Thermal Conductivity in Polymers Using Infrared Thermography

A new experimental method based on infrared thermography (IRT) is developed to study deformation-induced anisotropic thermal conductivity in polymers. An analytic solution for the temperature field of samples heated by a point source is utilized with a robust fitting procedure allowing for quantitative measurement of two components of the normalized thermal conductivity tensor of uniaxially stretched samples. In order to validate the method, we compare measurements on a cross-linked polybutadiene network with those obtained from a previously developed technique based on forced Rayleigh scattering (FRS). We find excellent agreement between the two techniques. Uncertainty in the measurements using IRT method is estimated to be about 2–5%. The accuracy of the method and its potential application to nontransparent materials make it a good alternative to extend current research on anisotropic thermal transport in polymeric materials.

Olefin Metathesis for Effective Polymer Healing via Dynamic Exchange of Strong Carbon–Carbon Double Bonds

In this article, we demonstrate transition-metal-catalyzed olefin metathesis as a simple, effective method for healing polymers via dynamic exchange of strong carbon-carbon double bonds. Upon introducing a very low level of the Grubbs' second-generation Ru metathesis catalyst into cross-linked polybutadiene (PBD) network, the material self-heals effectively at various conditions under moderate pressures. In sharp contrast, catalyst-free control samples with identical network topology and cross-linking density show minimal healing. The healing efficiency of the materials was carefully investigated under different concentrations of the Ru catalyst, compression pressures, and temperatures. It is demonstrated for the first time that a bulk polymer could effectively heal via dynamic covalent bond formation at sub-ambient temperature. The Ru-loaded PBD samples not only heal well with themselves but also with control samples without any catalyst. Furthermore, a completely Ru-free PBD network can heal effectively upon simply applying a very small amount of Ru catalyst only at the fracture surface. The simplicity and effectiveness of this self-healing approach make it potentially applicable to a wide range of olefin-containing polymers.

Making Insoluble Polymer Networks Malleable via Olefin Metathesis

Covalently cross-linked polymers have many technological applications for their excellent properties, but they suffer from the lack of processability and adaptive properties. We report a simple, efficient method of generating adaptive cross-linked polymers via olefin metathesis. By introducing a very low level of the Grubbs' second-generation Ru metathesis catalyst, a chemically cross-linked polybutadiene network becomes malleable at room temperature while retaining its insolubility. The stress relaxation capability increases with increasing level of catalyst loading. In sharp contrast, catalyst-free control samples with identical network topology and cross-linking density do not show any adaptive properties. This chemistry should offer a possibility to combine the dimensional stability and solvent resistance of cross-linked polymers and the processability/adaptibility of thermoplastics.

Design of nonaqueous polymer gels with broad temperature performance: Impact of solvent quality and processing conditions

Polymer gels have potential use for a wide variety of applications, primarily due to the ability to tailor the gel properties by varying several material parameters. While substantial attention has focused on water-based hydrogels, the use of these materials is limited due to a narrow operational temperature range. This report describes a nonaqueous polymer gel, composed of a cross-linked polybutadiene network swollen with low volatility polymer plasticizers. Thermal, mechanical, and adhesive characterization illustrated that the gels exhibit performance over an extremely broad temperature range (−60–70 °C). Solvent quality and loading played a critical role in the operational temperature window with small solvent solubility parameter deviations dramatically reducing the operational temperature range. In addition, the processing conditions had a large impact on the gel mechanical properties. As a result, it is important to consider the influence of processing conditions and solvent quality when tailoring polymer gels for practical applications.

Deuterium NMR study of the microscopic deformation and chain dynamics of polybutadiene networks

2H NMR measurements on carbon-black-filled&crosslinked polybutadiene (PB) networks and unfilled counterpart reveal the strong uniaxial-elongation dependence of both the transverse relaxation rate (1/T 2) and the splitting distance (Δν) of NMR lineshape; furthermore, the fluctuating part, instead of the static residual part, of quadrupolar interaction is found to govern the transverse relaxation signal at large deformation ratios (e.g., λ extt1.5) or high filler loads (e.g., 25phr or higher). The comparison of the T 2's or Δν's in both unfilled and filled cases and in the cases of different λ ext's indicates that in filled cases, the rubber matrix does not undergo overstrain in a wide range of λ ext, and chain breakage is prevented. This is also supported by the environmental scanning electron microscopy evidence for the deformation of carbon black clusters/network. In contrast, the unfilled PB network tends to undergo inhomogeneous deformation as λ ext increases, as confirmed by more than one 2H NMR doublets.

Thermomechanical and Morphological Characteristics of Cross‐Linked GAP and GAP–HTPB Networks with Different Diisocyanates

AbstractThis paper describes the mechanical and thermal characterisation of cross‐linked glycidyl azide polymer (GAP) and GAP–hydroxyl terminated polybutadiene (HTPB) networks. Cross‐linked GAP and GAP–HTPB networks were prepared by reacting GAP diol and GAP–HTPB diol mixture with different diisocyanates. The physical and mechanical characteristics were found to be influenced by the type of isocyanate curing agents, [NCO]/[OH] equivalent ratios and concentration of GAP. For all the three types of curing agents, GAP–HTPB blends of 50 : 50 to 30 : 70 ratios show higher mechanical strength over the virgin networks of GAP or HTPB. Thermal decomposition of cross‐linked GAP–HTPB networks was evaluated by thermogravimetric analysis (TGA). The kinetic parameters for the decomposition of GAP–HTPB blends were found to be dependant on the concentration of GAP and HTPB in the blend. The cross‐linked GAP–HTPB blends were subjected to dynamic mechanical analysis (DMA). The glass transition characteristics of the blends were evaluated by DMA and it was found that blends prepared with GAP content up to 30% showed single transition in the loss tangent trace indicating no phase separation in the cured network.

Synthesis and characterization of conducting interpenetrating polymer networks for new actuators

The synthesis of conducting interpenetrating polymer networks (IPNs) for actuator applications is described. The IPNs are synthesized from poly(ethylene oxide) and polybutadiene networks in which the conducting polymer (poly(3,4-ethylenedioxythiophene)), PEDOT, is gradually dispersed, i.e. its content decreases from the outside towards the centre of the film. The conducting IPN morphology was investigated by electrical resistance measurements and DMA. For actuation experiments, aqueous or organic electrolyte solutions were used but the best results were obtained with a room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide (EMITFSI).

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 =...

Analysis of deuterium NMR spectra of probe chains diffusing in a stretched polybutadiene network

Polybutadiene network was swollen with short perdeuterated network-like chains (PBD). Deuterium NMR spectra of these probe chains are measured as the rubber matrix is uniaxially elongated. Due to the presence of two kinds of deuterons (methylene and ethylene) and two possible configurations of monomer units ( cis and trans) in PBD chains, composite NMR spectra are observed and analysed. They evidence for different orientational behaviour of cis and trans units. ‘Rod-like’ motional behaviour of the trans units leads to higher degree of orientational order than for the cis units.

Phase behavior of a nematic liquid crystal in polybutadiene networks

Phase behavior of polybutadiene (PB) networks swollen in nematic liquid crystal p-ethoxybenzylidene- p- n-butylaniline (EBBA) strongly depends on whether there is surrounding EBBA: without the surrounding EBBA, EBBA in PB networks fails to form the nematic phase; in the presence of the surrounding EBBA, the nematic phase is formed inside the gels. The results suggest that a high order of molecular alignment in the surrounding nematic EBBA induces the formation of nematic phase inside the gels and the inducement effects overcome a high dilution effect of the impurity (PB) on the interaction between EBBA molecules.

Swelling of sodium chloride filled polybutadiene networks in water, water/ acetone and water/THF mixtures

The swelling of polybutadiene (PB) networks of different cross-link densities filled with finely divided sodium chloride (NaCI) particles are studied in water, water/acetone and water/THF mixtures. Swelling over periods of 2 months are recorded. The degree of swelling was observed to increase continuously in water during this period, whereas in water/acetone mixtures it reached a peak followed by deswelling and it converged to a maximal value in water/THF mixtures. The highly cross-linked samples exhibited unusually high degrees of swelling, and calculations indicated full stretching of the network chains. The enthalpic contribution to the chemical potential of the networks in equilibrium with solvent was determined using the phantom network model of rubber elasticity theory. The swollen network-salt system was approximated by the lattice model of polymer solutions. The positive contributions of water and acetone to the chemical activity of the swollen network were offset by the negative contribution of dissociation of salt in water, resulting in a small negative enthalpy of mixing. The highest rate of diffusion of solvent was observed for the PB/water/THF ternary system. Diffusion rates of pure water and water/acetone mixture were much smaller and of comparable magnitude. Mechanical measurements of stress and strain at break, and dynamic mechanical measurements of storage and loss moduli of filled and unfilled samples showed that filling with NaCl did not change the mechanical properties of the networks significantly, in spite of the dramatic change in the swelling behaviour.

Random Polybutadiene Rubber Networks with Unattached Chains

The preparation and characterization of randomly cross-linked polybutadiene (PB) networks containing unattached PB chains are presented. These were used as model systems for the experimental study of the dynamics of linear chains trapped in networks, which is the basic model of the reptation-in-a-tube model of Doi and Edwards. The preparation consists of the conversion at random of a small fraction of the PB chains' double bonds into epoxide groups and in the subsequent selective use of these as cross-linking centers in the presence of unmodified PB chains; these last remain chemically unattached to the network. The selectivity of the cross-linking reaction was examined by swelling−extraction of networks containing known fractions of relatively short “monodisperse” unattached chains. The polymeric phase composition of the networks with unattached chains (nuc) was tested by glass transition temperature measurements. Dynamic−mechanical measurements were shown to be sensitive to the polymer-phase composition of nuc, as well. The dynamics of the linear PB chains in the melts and in the networks was studied by dynamic−mechanical measurements. The experimental results for the longest relaxation time τL were compared with the predictions of the reptation-in-a-tube model with and without chain-end effects. Within experimental accuracy, the obtained scaling of τL relative to the chain mass M (up to 9 × 105 g/mol) is the same in both media: τL ∼ Mx with x = 3.35 (±0.10 as against x = ±3 from the pure reptation-in-a-tube model; correcting for chain-end effects in the form of contour length fluctuation, results in a good description of the experimental data for the τLs of unattached chains. τL for the chains trapped in networks were found to be 1.9−3.2 times longer than the τL of the respective melts. Data on 14 PB prepared by anionic polymerization and covering the range of weight average molar masses 1.0 × 104 to 1.5 × 106 g/mol are presented.

Field-cycling nuclear magnetic resonance relaxometry of thermoreversible polybutadiene networks

Chain dynamics in thermoreversible polybutadiene networks were studied in comparison to linear polybutadiene using field-cycling NMR (nuclear magnetic resonance) relaxometry. The effect of rapidly fluctuating cross links on the chain mode relaxation time is shown to result in dynamics rescaled according to a new effective segmental friction coefficient. The frequency dependence of the spin-lattice relaxation time consists of a sequence of three regions characterized by power laws with exponents 0.5±0.05, 0.25±0.05, and 0.44±0.05 from high to low frequencies (and low to high temperatures). Thermoreversible cross-linking shifts the crossover frequencies toward lower values. In our previous work on linear polymers these frequency dependences were shown to be a consequence of the once (or twice) renormalized Rouse theory. The same formalism can be used for the thermoreversible polybutadiene networks by rescaling the segmental relaxation time.