Effects of Binding Energy of Bioinspired Sacrificial Bond on Mechanical Performance of <Emphasis Type="Italic">cis</Emphasis>-1,4-Polyisoprene with Dual-crosslink

Although bioinspired sacrificial bonds have been demonstrated to be efficient in improving the mechanical properties of polymer materials, the effect of binding energy of a specific dynamic bond on the ultimate mechanical performance of a polymer network with dual-crosslink remains unclear. In this contribution, diamine and sulfur curing package are introduced simultaneously into a sulfonated cis-1,4-polyisoprene to create dually-crosslinked cis-1,4-polyisoprene network with sulfonate-aminium ionic bonds as the sacrificial bonds. Three diamines (primary, secondary and tertiary) with the same spacer between the two nitrogen atoms are used to create the ionic bonds with different binding energies. Although the binding energy of ionic bond does not affect the glass transition temperature of cis-1,4-polyisoprene (IR), it exerts definite influences on strain-induced crystallization and mechanical performance. The capabilities of diamine in dissipating energy, promoting strain-induced crystallization and enhancing the mechanical performance are in the same order of secondary diamine > primary diamine > tertiary diamine. The variations in mechanical performances are correlated to the binding energy of the ionic bond, which is determined by pK_a values.     

异戊橡胶微观序列结构与结晶性能研究

天然橡胶特有的应变诱导结晶能力赋予其优异的力学性能.异戊橡胶作为唯一能够替代天然橡胶的合成橡胶品种,其应变诱导结晶能力受到关注.本文对3种异戊橡胶的微观序列结构进行了分析,并研究了其结晶性能.核磁分析结果表明:3种异戊橡胶的顺-1,4-结构含量差别不大;从1,4-结构单元的键接方式(序列结构)看,SKI-5和YS-IR分子链中顺-1,4-结构单元均以头-尾相接的方式沿分子链排列,不存在头-头键和尾-尾键接方式;SKI-3中约有0.4%~0.5%的1,4-单元采取头-头键接方式,约有0.3%~0.6%的1,4-单元采取尾-尾键接方式;根据定量计算结果,从分子链上1,4-结构单元的序列分布来看,SKI-3的规整性与SKI-5、YS-IR相近或略高.XRD研究结果表明:炭黑填充的天然橡胶硫化胶拉伸至400%以上时发生取向结晶;而炭黑填充的异戊橡胶硫化胶需拉伸至500%以上时才发生取向结晶.基本物理机械性能研究表明:3种异戊橡胶的性能相当,拉伸强度和撕裂强度明显低于天然橡胶;由于结构和组成上的差异,异戊橡胶的结晶能力较天然橡胶差.     

Study of crystallization kinetics of trans-1,4-polyisoprene

The concentrations and the growth rates of high- and low-melting type spherulites of trans-1,4-polyisoprene were measured in the temperature range 39–49°C. It was shown that above about 40°C., the crystallization rate of trans-1,4-polyisoprene is determined primarily by the radial growth rate of high-melting form (HMF) spherulites, whereas the predominance of the low-melting form (LMF) crystals below 40°C. can be attributed to the high rate of formation of LMF primary nuclei at lower crystallization temperatures. Temperature-independent rate parameters were calculated from optical and dilatometric measurements and were found to be in good agreement. Both the change in nucleation habit and spherulite growth rate with temperature can be explained on the basis of a lower end surface free energy of LMF crystals of trans-1,4-polyisoprene compared to that of the HMF crystals.     

Reactions of singlet oxygen with polyisoprene and model compounds

Results from the study of singlet oxygen reaction with cis-1,4-polyisoprene and with various models are compared. The nature of the products and their reactivity are discussed for two kinds of models, namely oligodienes and trisubstituted mono-olefins with various substituent length. The reactivity of the double bond decreases with lengthening of the alkyl substituents but the reactivity of 4-methyl-4-octene is close to that of the polymer. The hydroperoxidation of a unit in an oligodiene does not deactivate significantly the adjacent units towards singlet oxygen addition. The reactivity of the allylic hydrogen a, b, and c in the olefin

depends on both the position and the length of the substituents and follows the sequences K _c > k _b > k _a. The principle of syn-ene addition can be extrapolated to polyisoprene. The rate constant determined for the cis-1,4-polyisoprene ¹O₂ reaction allows the conclusion that the probability of reaction of ¹O₂ with the solid polymer may be high. Similarity in the behaviour of polymer and models in this reaction allows for the estimation of the reactivity of other unsaturated or reactive polymers towards ¹O₂.     

Can nature's design be improved upon? High strength, transparent nacre-like nanocomposites with double network of sacrificial cross links

The preparation of a high-strength and highly transparent nacre-like nanocomposite via layer-by-layer assembly technique from poly(vinyl alcohol) (PVA) and Na+-montmorillonite clay nanosheets is reported in this article. We show that a high density of weak bonding interactions between the polymer and the clay particles: hydrogen, dipole-induced dipole, and van der Waals undergoing break-reform deformations, can lead to high strength nanocomposites: sigmaUTS approximately 150 MPa and E' approximately 13 GPa. Further introduction of ionic bonds into the polymeric matrix creates a double network of sacrificial bonds which dramatically increases the mechanical properties: sigmaUTS approximately 320 MPa and E' approximately 60 GPa.     

Multi-bond network hydrogels with robust mechanical and self-healable properties

Multi-bond network(MBN) which contains a single network with hierarchical cross-links is a suggested way to fabricate robust hydrogels. In order to reveal the roles of different cross-links with hierarchical bond energy in the MBN, here we fabricate poly(acrylic acid) physical hydrogels with dual bond network composed of ionic cross-links between carboxylFe3+ interactions and hydrogen bonds, and compare these dually cross-linked hydrogels with singly and ternarily cross-linked hydrogels. Simple models are employed to predict the tensile property, and the results confirm that the multi-bond network with hierarchical distribution in the bond energy of cross-links endows hydrogel with effective energy-dissipating mechanism. Moreover, the dually cross-linked MBN gels exhibit excellent mechanical properties(tensile strength up to 500 k Pa, elongation at break ~ 2400%) and complete self-healing after being kept at 50 °C for 48 h. The factors on promoting self-healing are deeply explored and the dynamic multi-bonds are regarded to trigger the self-healing along with the mutual diffusion of long polymer chains and ferric ions.     

Mechanical and swelling equilibrium characterization of high cis-1,4-polyisoprene networks

Equilibrium stress-strain relationships in uniaxial extension for high cis-1,4-polyisoprene (Shell IR 307) networks were obtained by extrapolation of relaxation measurements to infinite time through a Bernstein-Kearsley-Zapas (BKZ) constitutive equation. Three series of networks were investigated, each series being characterized by its polymer precursor molecular weight. The influence of cross-linking density was studied through varying amounts of dicumyl peroxide as cross-linking agent. These results were used to test Flory and Erman's recent molecular theory of networks with constraints on junctions. Swelling equilibrium experiments with benzene and cyclohexane were performed on these networks and were in agreement with the mechanical analysis. The polymer-solvent interaction parameter for the system cis-polyisoprene + cyclohexane was estimated to be 0.31 at 20°C in the range 0 to 0.2 of polymer volume fraction.     

~(13)C-NMR研究3,4-聚异戊二烯的序列分布

Fe(acac)_3-Phen-AlEt_3 催化体系可使异戊二烯聚合成以 3,4-链节为主具有一定结晶性能的聚异戊二烯。本文对该聚合物的~(13)C-NMR 谱进行了全分析,研究了序列分布、微观结构。结果表明不同方法求得的微观结构含量很好地一致,说明对~(13)C-NMR 谱峰归属的正确性。并指出顺-1,4/3,4-序列中存在着头-头,尾-尾的连接方式,3,4-嵌段链节不足够长及存在反节可能是结晶度不太高的主要原因。     

NONCONJUGATED CONDUCTIVE POLYMERS

Conjugation is not a prerequisite for a polymer to be conductive. A polymer must have at least one double bond in the repeat to become conductive. Interaction with a dopant (e.g., electron acceptor) causes transfer of an electron from the double bond to the dopant creating a hole at the double bond site. Electrical conduction occurs via intersite hopping of holes. Various spectroscopic methods (FTIR, optical absorption, solid-state ¹³C NMR, etc.) along with electrical measurements have been used to elucidate the mechanism of conduction in specific nonconjugated conductive polymers. Examples of these polymers include 1,4-polyisoprene which has one double bond and three single bonds in the repeat. The conductivity of polyisoprene increases 100 billion times upon doping with iodine to a maximum value of 10 S/m. Polyisoprene (natural rubber) is used nonconjugated conductive polymers have a wide range of applications in antistatics, various sensors and optoelectronics.     

Toughening a Self‐Healable Supramolecular Polymer by Ionic Cluster‐Enhanced Iron‐Carboxylate Complexes

Supramolecular polymers that can heal themselves automatically usually exhibit weakness in mechanical toughness and stretchability. Here we exploit a toughening strategy for a dynamic dry supramolecular network by introducing ionic cluster‐enhanced iron‐carboxylate complexes. The resulting dry supramolecular network simultaneous exhibits tough mechanical strength, high stretchability, self‐healing ability, and processability at room temperature. The excellent performance of these distinct supramolecular polymers is attributed to the hierarchical existence of four types of dynamic combinations in the high‐density dry network, including dynamic covalent disulfide bonds, noncovalent H‐bonds, iron‐carboxylate complexes and ionic clustering interactions. The extremely facile preparation method of this self‐healing polymer offers prospects for high‐performance low‐cost material among others for coatings and wearable devices.     

EFFECTS OF DILUTION DURING CROSSLINKING ON STRAIN-INDUCED CRYSTALLIZATION IN CIS-1,4-POLYISOPRENE NETWORKS. II. COMPARISON OF EXPERIMENTAL RESULTS WITH THEORY

ABSTRACT

Modern rubber elasticity theory was applied to the strain-induced crystallization results summarized for cis-1,4-polyisoprene in the preceding paper. The calculations adopted the basic assumptions made in the Flory crystallization theory, in some cases retaining the original affine elasticity model and in others adopting the new constrained-junction model. Of the two sets of theoretical stress-strain isotherms thus obtained, those from the constraint theory gave a good account of the experimental results. One major accomplishment was documenting the expected decrease in the constraint parameter κ with increase in dilution during crosslinking. This decrease is due to the fact that the diluting solvent decreases chain interpenetration, which in turn decreases entanglement constraints on the junction fluctuations.     

NMR spectroscopic investigation of multi-walled carbon nanotubes modified by amino groups

The results of the functionalization of multi-walled carbon nanotube surface by amines containing different substituents at the nitrogen atom, namely, primary n-hexylamine, secondary izadrine, and tertiary N-benzylmorpholine and dithiline, are presented. It was shown by NMR spectroscopy, thermal analysis, mass spectrometry, X-ray photoelectron spectroscopy, and elemental analysis that the interaction of primary and secondary amines with modified nanotubes results in the formation of a covalent bond with the nitrogen atom of amines, while the reactions with tertiary amines afford quaternary ammonium salts; diamine is attached covalently through both amine groups.     

Simulation of polymer network formation: Connectivity considerations

The issue of connectivity in polymer networks is discussed by employing graph theory. Several topics are addressed, including the theory of rubberlike elasticity and computer simulations of network formation. The formulation of the partition function is reviewed and new applications are presented on the irradiation cure of polybutadiene and the sulfur vulcanization of cis(1,4)-polyisoprene and cis(1,4)-polybutadiene.     

Chemical reactions and reactivity of primary,secondary, and tertiary diamines with acid functionalized polymers

Reactive melt processing of different types of diamines with polyethylene containing carboxylic acid groups and polystyrene containing anhydride groups was carried out. The reactivity of primary, secondary, and tertiary diamines with these acid polymers was determined using various techniques. Molecular weight increases due to crosslinking were observed through (1) changes in the torque during the reactive processing, (2) decrease in melt flow indices, and (3) decrease in solubility of the reaction products. The chemical compositions of the reaction products were examined by Fourier transform infrared (FTIR) spectroscopy. Thermal analysis using differential scanning calorimetry (DSC) was carried out to determine the crystallization behavior, glass transition temperatures, and thermal stabilities of the reaction products. Results show that the primary amine is the most reactive towards carboxylic acid or anhydride groups followed by the secondary and then the tertiary amine. Anhydride groups on polymers are of higher activity towards secondary or primary amino groups than carboxylic acid groups in the nucleophilic acyl substitution reactions. Reaction products crosslinked with the primary diamine are less stable than their parent acidic polymers. On the other hand, crosslinking with the secondary or tertiary diamine gives products with higher thermal stability than the parent acidic polymers. The formation of reversible and irreversible crosslinks with different types of diamines is also reported. © 1992 John Wiley & Sons, Inc.     

Application of self seeding technique in regulating polymorphic transformations during non-isothermal bulk crystallization of polymers

Non-isothermal melt crystallization of trans-1,4-polyisoprene (TPIP) has been studied with the help of differential scanning calorimetry (DSC) and wide-angle x-ray diffraction. Self-seeding has been used for the controlled growth of polymorphs. Thus, self-seeding below 55° and below 71°C has led to the exclusive crystallization of and polymorphs, respectively, upon non-isothermal cooling of the polymer melt. These temperatures may vary slightly with the previous thermal history and molecular characteristics of the original sample. It has been interpreted that during cooling the rate of growth (by secondary nucleation) of seeds of either polymorph remains much faster than the rate of primary nucleation of the other polymorph whose seeds are not present in the melt. As a result, the crystallizing melt becomes occupied by the spherulites of the seeded polymorph well before the other polymorph can nucleate.     

基于壳聚糖物理网络的高强韧双网络水凝胶的构建、调控与应用

双网络水凝胶由两个具有相反物理性质的交联网络构成,硬而脆的第一网络在变形过程中断裂耗散能量,从而增韧凝胶.当第一网络为具有重建能力的物理网络时,双网络水凝胶表现出优异的抗软化和机械稳定性.目前双网络水凝胶第一物理网络类型单一、结构和力学调控繁琐,因而其开发和应用受到限制.针对上述问题,作者发展了硬而脆的壳聚糖物理网络构...     

Photoinduced microstructural changes in 1,4-polyisoprene

An infrared and NMR study was made of the microstructural changes produced in thin films of purified cis- and trans-1,4-polyisoprene when irradiated with ultraviolet light in vacuo at room temperature. The major photochemical processes observed were cis–trans isomerization and loss of 1,4 double bonds, the latter process being accompanied by the formation of vinylidene and vinyl double bonds as well as some endlinking. Very surprisingly, the loss of original double bonds contributed also to a novel photocyclization which gave rise to cyclopropyl groups in the polyisoprene chain. The isomerization and the formation of cycloprophyl groups are presumed to proceed through triplet and biradical states of the 1,4 double bonds, while the vinylidene and vinyl double bonds must result from chain repture at the carbon–carbon bond joining successive isoprene units. Hydrogen abstraction and double-bond migration are of neglible importance in the overall photochemistry of polyisoprene.     

Mechanopolymerchemie

Although many methods can be employed to transfer energy to a chemical reaction, mechanical energy has not been widely used: It is difficult to apply mechanical forces high enough to lead to breaking bonds to small molecules. Work is the product of force and displacement but when the distances are small, very high forces are needed to obtain sufficient energy to break a bond. The situation is different in polymers, where the path length can be high. Here, bond cleavage, cycloreversions and isomerisations can be observed when mechanical energy is supplied, both in solution and solid systems. Mechanical energy can lead to different mechanistic pathways than those observed under thermal conditions or irradiation. Practical applications of the mechanochemistry of polymers are only just emerging and range from a better understanding of polymer decomposition under force to the development of strain sensors using mechanochromic polymers.     

羟烷基胺功能化离子液体吸收SO_2的量子化学计算(英文)

采用量子化学中的密度泛函理论(DFT)对羟烷基胺离子液体(HyAAILs)与二氧化硫(SO2)的相互作用进行了研究.通过几何结构优化,电荷分布和热力学参数计算等来确定离子液体中能够有效吸收SO2的官能团.HyAAILs与SO2反应形成平均距离为0.240nm的S—N键,导致电荷从ILs转移到SO2以及S—O键长和O—S—O键角的改变.气态和液态模型的计算结果表明,标准吉布斯函数变(△G苓)主要取决于阳离子的结构和分子质量.阳离子结构影响了吸收反应能垒,对于三种阳离子体系的反应活化能顺序为:Ea(secondary)Ea(tertiary)Ea(primary).理论计算结果得到了实验数据的验证,羟乙基伯胺离子液体吸收的SO2理论摩尔分数与文献中的实验数据非常接近.本研究提供了一种预测和验证功能离子液体性质的有效方法.     

Synthesis of 1,4-polyisoprene support of 2-chloroethylphosphonic acid (ethephon), a stimulating compound for the latex production by the Hevea brasiliensis

2-Chloroethylphosphonic acid (ethephon) is a well known stimulating product used to improve the latex production by the rubber tree (Hevea brasiliensis). Its chemical fixation in side position of 1,4-polyisoprene chains by weak chemical bond was considered in order to prepare new derivatives having prolonged stimulating activity. The synthesis was considered by using a chemical modification procedure according to a two-step process. Firstly, an epoxidized 1,4-polyisoprene intermediate was prepared by partial epoxidation of 1,4-polyisoprene. Secondly, the grafting of 2-chloroethylphosphonic acid was achieved by using the reactivity of the P-OH acidic function (or a P-OSiMe₃ derived from P-OH) of the reagent toward oxirane rings of epoxidized 1,4-polyisoprene. It was noted that grafting yields are improved when the reaction is carried out in bulk or in a non-polar solvent, and more especially in neutral conditions, that is by replacing ethephon with its trimethylsilylated derivatives [monotrimethylsilyl 2-chloroethylphosphonic acid or, more especially, di(trimethysilyl) 2-chloroethylphosphonate]. With this latter, the addition occurs by the intermediate of the P-OSiMe₃ bond, and the formation of 2-oxo-l,3,2-dioxaphospholane structures is highly favored.