Comparison of Stress-Strain Relations of Polybutadiene Vulcanizates in Compression and in Extension

Abstract

According to elementary statistical theory of rubber elasticity, the modulus of rigidity τ/(λ - λ^?2) is constant. The phenomenological theory predicts that this modulus is in first approximation equal to the sum of a constant (2C₁) and a deformation-dependent term, 2C₂. The dependence on elongation of experimental modulus data of many elastomers agrees more or less with the C₂ term. Several attempts have been made to explain this dependence on the basis of molecular phenomena or by refinements of the statistical theory of elasticity. At present there is no consensus of opinion on the origin or interpretation of the deformation-dependent term. Almost all of the data on this dependence have been generated in extension experiments.     

端羟基聚丁二烯/环氧氯丙烷合成多羟基聚丁二烯的实验研究

在氢氧化钠碱性条件下,以端羟基聚丁二烯(HTPB)和环氧氯丙烷(ECH)为原料,四丁基溴化铵(TBAB)为催化剂,制得多羟基聚丁二烯(PHPB)。采用红外光谱(IR)、热重分析仪(TG)、核磁共振(1 H-MNR)对原料、中间产物和产物的结构和热稳定性进行了分析。通过产品的羟值、粘度和产率详细考察了反应温度、反应时间、原料配比、催化剂用量和氢氧化钠用量对PHPB合成的影响。结果表明,最适宜合成工艺条件为:反应温度为55℃,反应时间1.5h,n(HTPB)∶n(ECH)∶n(NaOH)∶n(TBAB)=1∶2.9∶3∶0.03。     

Mechanochemically Triggered Topology Changes in Expanded Porphyrins

A hitherto unexplored class of molecules for molecular force probe applications are expanded porphyrins. This work proves that mechanical force is an effective stimulus to trigger the interconversion between Hückel and Möbius topologies in [28]hexaphyrin, making these expanded porphyrins suitable to act as conformational mechanophores operating at mild (sub-1 nN ) force conditions. A straightforward approach based on distance matrices is proposed for the selection of pulling scenarios that promote either the planar Hückel topology or the three lowest lying Möbius topologies. This approach is supported by quantum mechanochemical calculations. Force distribution analyses reveal that [28]hexaphyrin selectively allocates the external mechanical energy to molecular regions that trigger Hückel–Möbius interconversions, explaining why certain pulling scenarios favor the Hückel two-sided topology and others favor Möbius single-sided topologies. The meso-substitution pattern on [28]hexaphyrin determines whether the energy difference between the different topologies can be overcome by mechanical activation.     

Relation between Energy Contribution to Elastic Force and Strain Dependence of Modulus for Polybutadiene Vulcanizates

It is well known that the modulus G = r/(λ - λ^?2) varies with deformation, thus deviating from the predictions of statistical theories of rubber elasticity which require it to be constant. It has also been found that there is a nonnegligible energy contribution to the elastic force. It is postulated that these two phenomena are related because both arise from energetic interaction between chains.

Based on the lateral order of chains indicated by x-ray fiber diagrams of elongated noncrystallizable elastomers, it is suggested that energetic interaction of chains is induced by strain orientation. Proportionality between these two is assumed. The orientation distribution functions of end-to-end vectors and of statistical chain segments are considered. The proportionality constants are determined from the energy contribution to the strain dependence of the coefficient of thermal expansion. With the aid of these constants the modulus, corrected for energy contribution, is calculated. The observed and calculated elongation dependence of G agree reasonably well.

It is concluded that an energy interaction between aligned chains can account for the deviation of the observed stress elongation relation from the predictions of entropy elasticity theories.     

Synthesis and Flammability of Bromine-Containing Polybutadiene

COOH-terminated polybutadiene has been converted into COCl-terminated polybutadiene which was further chemically cross-linked with bisphenol-A and tetrabromobisphenol-A. The flammability characteristics of bisphenol-A and tetrabromobisphenol-A resins have been examined using thermogravimetric, ignition temperature and mass burning rate data. Mass burning rate results support that tetrabromobisphenol-A cross-linked polybutadiene is flame retardant compared to the corresponding non brominated compositions.     

Solvent Effect in Swelling of Butyl Rubber and Polybutadiene

Relationship between the swellabilities of butyl rubber and polybutadiene in organic solvents and the physicochemical characteristics of solvents, including their capability for nonspecific and specific solvation, was studied.     

Theory of Shear‐Thickening in Transient Networks of Associating Polymers

Summary: Shear‐thickening phenomena observed in thermo‐reversible gels of telechelic associating polymers are theoretically studied on the basis of the transient network model. Non‐linear tension due to over‐stretching of the middle chain leads to thickening, if the coupling constant g of the end‐chain dissociation rate to the middle chain tension fulfills a certain condition. We give the condition for thickening in terms of the molecular parameters.

The thickening phase diagram: The region below each curve leads to thickening, whereas the region above the curve causes thinning for each molecular weight.     

基于金属配位键的自修复、可重塑聚丁二烯橡胶的合成及性能

橡胶材料通常因经过硫化及补强等工艺处理而呈现出热固性,因而难以被回收处理,容易造成严重的资源浪费和环境污染.本文通过在聚丁二烯上修饰羧酸基团,再加入锌离子(Zn2+)与羧酸配位,制备了基于金属配位键交联的自修复橡胶(PB-COOH/Zn2+).该橡胶具有良好的机械性能和优秀的自修复及重塑性能,在70℃下修复3 h,其韧性可以恢复到初始强度,修复效率可达100%. PB-COOH/Zn2+较高的聚合物链段运动能力及配位键交联网络良好的动态性不仅赋予其优异的修复性能,还使得其在较温和的条件下可以进行多次重塑,在70℃及5 MPa的条件下重塑3次仍能保持原有的机械性能.此外,通过在PB-COOH/Zn2+中掺杂适量的碳纳米管,不仅增强了其机械性能,还使其具备了电致修复及传感能力,扩宽了PB-COOH/Zn2+作为环境友好型材料的应用前景.     

Characterizations of Thermoplastic Block Elastomers Based on Polybutadiene and ε -Caprolactone

A broad series of tri- and multiblock copolymers based on linear and branched oligomers of polybutadiene as central blocks and polycaprolactone (PCL) as block extremities are characterized by SEC, DSC, DMA, Dynamical Rheology and DRX. DSC analyses reveal phase separation between the two amorphous PB and PCL phases. By thermal analysis, the glass transition temperature of PCL is only detected for materials containing at least 80% w/w of PCL. This is attributed to the small length of the polyester blocks for copolymers containing less than 80% w/w of PCL. The increase of fusion heat with increasing PCL content in the copolymers is correlated to the greater ability of PCL chains to rearrange as HTPB amount decrease in the material. Regarding the evolution of the melting temperature of the various copolymers, the characterization by DMA and dynamical rheology confirms the behaviour observed by DSC. Mechanical and rheological properties (i.e., storage modulus and complex viscosities) were studied and reveal that the behavior of the copolymers depends on both the rate of PCL chains and on the nature of the elastomeric block.     

Effect of the Number of Subnetworks on the Topology and Mechanical Properties of Interpenetrating Networks: Computer Simulation

The mechanical properties of solvent-fks obtained by three different crosslinking mechanisms are investigated by the dissipative particle dynamics method. It is shown that, upon crosslinking without additional conditions (the vulcanization model), the amount of defects increases with an increase in the number of subnetworks, thereby worsening the rigidity of the system. If crosslinking mechanisms excluding formation of a certain kind of defects are used, that is, the network topology approaches the ideal one, interpenetrating networks with a higher number of subnetworks, on the contrary, demonstrate a higher rigidity owing to the fact that subchains in them are more strained. This effect is not observed in networks synthesized upon crosslinking without additional conditions. The reasons for this behavior and probable experimental analogies are discussed.     

Volumetric Changes of Randomly Crosslinked Model Networks

Equilibrium P–V–T properties of randomly crosslinked amorphous polymer networks are modeled via molecular dynamics simulation for connectivity ratios between 1.0 and 1.5. The relation between connectivity ratio and network shrinkage is studied over a wide range of temperatures and pressures. The simulation results are compared to a mean‐field Flory–Huggins lattice model.

     

Short Comments on Kinetic Models Involving Changes in Activation Energy

Journal of Thermal Analysis and Calorimetry -     

Chain-extending of Hydroxytelechelic Polybutadiene: Synthesis and Characterization

Extension of hydroxytelechelic polybutadiene oligomers ( 3200 g/mol) is performed in mild conditions, in order to avoid backbone modifications, using succinic anhydride or methylenedicyclohexyl diisocyanate. The two routes present significative extension of the initial oligomers. Extension through the anhydride route, in the presence of DCC and DMAP, leads to new hydroxytelechelic oligomers ( 8000 g/mol). Extension through the diisocyanate route, catalyzed by DBTL at 65°C leads to hydroxytelechelic oligomers of higher average molecular weight ( 20000 g/mol). New materials are characterized by FTIR/¹H-NMR and changes in their Tg according to , are discussed. The influence of reaction time on the length of the macromolecular chains is also studied.     

Controlling Topology within Halogen-Bonded Networks by Varying the Regiochemistry of the Cyclobutane-Based Nodes

The formation of a pair of extended networks sustained by halogen bonds based upon two regioisomers of a photoproduct, namely rctt-1,3-bis(4-pyridyl)-2,4-bis(phenyl)cyclobutane (ht-PP) and rctt-1,2-bis(4-pyridyl)-3,4-bis(phenyl)cyclobutane (hh-PP), that have varied topology is reported. These networks are held together via I⋯N halogen bonds between the photoproduct and the halogen-bond donor 1,4-diiodoperchlorobenzene (C₆I₂Cl₄). The observed topology in each solid is controlled by the regiochemical position of the halogen-bond accepting 4-pyridyl group. This paper demonstrates the ability to vary the topology of molecular networks by altering the position of the halogen bond acceptor within the cyclobutane-based node.     

Stereoselective Complex Formation between Polybutadiene and Cyclodextrins in Bulk

Polybutadienes (PBs) are found to form inclusion complexes with cyclodextrins (CDs) stereoselectively to give crystalline compounds in bulk. These complexes have been isolated and characterized by means of ¹H NMR and ¹³C CP/MAS NMR spectroscopy, and X‐ray diffraction. Although α‐CD did not form inclusion complexes with any kinds of PBs in aqueous solutions, α‐CD did form inclusion complexes with PBs having 1,4‐cis‐ and 1,4‐trans‐butadiene units in bulk by heating at 100 °C. On the other hand, PB having 79% of a 1,2‐structure did not form inclusion complexes with α‐CD. The yield of the inclusion complexes increases with an increase in the content of the 1,4‐cis‐structure of PB and decreases with the molecular weights of the PBs.

     

聚丁二烯聚氨酯(脲)

综述了聚丁二烯聚氨酯（脲）的结构与性能，影响性能的因素和改性方法，并简要介绍了其应用。     

Radiation and Chemical Grafting of Styrene to Polybutadiene Latex

Earlier studies of the gamma radiation and potassium persulfate grafting of styrene to uncrosslinked small particle size polybutadiene latices have been extended to a commercial cross-linked large particle size latex. The larger size particles and high gel content of the substrate latex was found to lead to a more complicated pattern of behavior. The conversion curves and the molecular weights were found to be complex functions of the initial monomer concentration, number of particles and temperature with both methods of initiation. The simple Smith-Ewart theory did not, in general, apply to these systems, and the k_p and E_p varied with conditions and were not in agreement with the generally accepted literature values. The molecular weights of the extracted polystyrene homopolymer were lower in the case of radiation initiation, in agreement with the previous work. This suggests that shorter but numerous grafted side chains are possible with radiation presumably due to the higher radical fluxes. (Some parallel experiments indicated that the molecular weights of the extracted homopolystyrene are similar to those of the grafted side chains.) This phenomenon also leads to somewhat lower graft efficiency with radiation initiation. Nevertheless, radiation was found to give grafting efficiencies of more than 80% under the best conditions. The conversions were also quite efficient with economical yields per radiation dose. These results, coupled with the ease of control and other features of radiation, make it a viable alternative method of initiation for industrial use.     

Effect of Supramolecular Interchain Sticking on the Low‐Frequency Relaxation of Transient Polymer Networks

Supramolecular polymer networks and gels often exhibit three effects in rheology as a function of increasing strength and extent of transient chain interlinkage: (i) the longest relaxation time increases, (ii) the elastic part of the complex shear modulus on timescales longer than that increases, and (iii) the frequency‐dependent power‐law scaling of this modulus gets shallower in this regime. In a recent report, these effects have been systematically assessed by comparing transient polymer networks derived from a common precursor modified with different extents of a common hydrogen‐bonding supramolecular sticker. In this communication, complementary studies are discussed that are based on a set of polymers also derived from a common precursor but all modified with the same extent (4.8%) of very different supramolecular crosslinking motifs. This comparison reveals that effect (iii) can be rationalized by exacerbation of polydispersity effects to the relaxation time spectrum if supramolecular interchain sticking is present. In addition, effect (ii) is addressable to a simple thermodynamic argument that appraises the supramolecular sticking contribution to the elastic part of the shear modulus in the relaxation regime.

     

Ultrafast Manipulation of Transient Energy Transfer Between Surface Plasmons and Resonators in Hybrid Nano-coupling System

Surface-plasmon(SP) modes triggered on metal nanostructures were strongly coupled to the local restricted electronmagnetic field supported by a Fabry-Perot(F-P) cavity. This hybrid system provided an ideal platform to study the interaction between SP and F-P resonators on nanoscales. However, the time-resolved transient energy transfer process is far from resolved. In this letter, we addressed this question by time-resolved femtosecond pump-probe technology and readily observed the transient energy transfer between SP and nanocavity resonant energy. The interaction resulted in the emergence of hybrid splitting mode and the oscillating dynamics between upper and lower polariton branch(the split hybrid states). Our work may provide a well comprehension of strong coupling between SP modes and F-P resonator modes, and lay some groundwork for many future photonic applications.