粘度法研究明胶在聚氨酯弹性体表面的吸附

根据文献以异佛尔酮二异氰酸酯（IPDI）为原料制备了具有较好机械性能的聚氨酯弹性体胶条（PU）,并在胶条表面接枝肝素,得到肝素化聚氨酯胶条（PU-Hep）。将聚氨酯胶条浸泡在明胶稀溶液中,测量溶液粘度随时间、溶液浓度和温度的变化,并采用具有界面校正的粘度方程从实验相对粘度数据计算明胶在聚氨酯表面的吸附量。研究发现明胶分...     

THEORY OF DIELECTRIC ELASTOMERS

In response to a stimulus, a soft material deforms, and the deformation provides a function. We call such a material a soft active material （SAM）. This review focuses on one class of soft active materials： dielectric elastomers. When a membrane of a dielectric elastomer is subject to a voltage through its thickness, the membrane reduces thickness and expands area, possibly straining over 100%. The dielectric elastomers are being developed as transducers for broad applications, including soft robots, adaptive optics, Braille displays, and electric generators. This paper reviews the theory of dielectric elastomers, developed within continuum mechanics and thermodynamics, and motivated by molecular pictures and empirical observations. The theory couples large deformation and electric potential, and describes nonlinear and nonequilibrium behavior, such as electromechanical instability and viscoelasticity. The theory enables the finite element method to simulate transducers of realistic configurations, predicts the efficiency of electromechanical energy conversion, and suggests alternative routes to achieve giant voltage-induced deformation. It is hoped that the theory will aid in the creation of materials and devices.     

Polypropylene ionic thermoplastic elastomers: Synthesis and properties

Polypropylene ionic thermoplastic elastomers have been prepared by melt radical grafting of maleic anhydride onto polypropylene in the presence of N-bromosuccinimide followed by neutralization of the resulting elastomeric grafted polypropylene using sodium salts. Sodium hydroxide and sodium acetate were compared in aqueous solution, as anhydrous or hydrated powders. The neutralization reaction was followed by Fourier transform infrared spectroscopy, allowing the development of a method to determine the effective neutralization degree. Important physical changes were recorded upon neutralization. Especially thermal stability, shear storage modulus and complex viscosity in the flow region were largely increased as a function of the neutralization degree.     

Thermomechanical modeling of the thermo-order-mechanical coupling behaviors in liquid crystal elastomers

Liquid crystal elastomer is a kind of anisotropic polymeric material, with complicated micro-structures and thermo-order-mechanical coupling behaviors. In this paper, we propose a method to systematically model these coupling behaviors. We derive the constitutive model in full tensor structure according to the Clausius-Duhem inequality. Two of the constitutive equations represent the mechanical equilibrium and the other two represent the phase equilibrium. Choosing the total free energy as the combination of the neo-classical free energy and the Landau-de Gennes nematic free energy, we obtain the Cauchy stress-deformation gradient relation and the order-mechanical coupling equations. We find the analytical homogeneous solutions of the deformation for the typical mechanical loadings, such as uniaxial stretch, and simple shear in any directions. We also compare the compression behavior of prolate liquid crystal elastomers with the stretch behavior of oblate liquid crystal elastomers. As a result, the stress, strain, temperature, order parameter, biaxiality and the direction of the director of liquid crystal elastomers couple with each other. When the prolate liquid crystal elastomer sample is stretched in the direction parallel to its director, the deviatoric stress makes the mesogens more order and increase the transition temperature. When the sample is sheared or stretched in the direction non-parallel to the director, the director of the liquid crystal elastomer will rotate, and the biaxiality will be induced. Because of the order-mechanical coupling, under infinitesimal deformation, liquid crystal elastomer has anisotropic Young’s modulus and zero shear modulus in the direction parallel or perpendicular to the director. While for the oblate liquid crystal elastomers, the stretch parallel to the director will cause the rotation of the director and induce the biaxiality.     

Multigraft copolymer superelastomers: Synthesis morphology, and properties

The synthesis of well-defined multigraft copolymers having a polydiene backbone with polystyrene side chains is briefly reviewed, with particular focus on controlling branch point spacing and branch point functionality. Use of living anionic polymerization and chlorosilane linking chemistry has led to the synthesis of series of materials having regularly spaced trifunctional (comb), tetrafunctional (centipede), and hexafunctional (barbwire) branch points. The morphologies of these materials were characterized by transmission electron microscopy and small-angle X-ray scattering, and it was found that the morphologies were controlled by the local architectural asymmetry associated with each branch point. Mechanical properties studies revealed that such multigraft copolymers represent a new class of thermoplastic elastomers (TPEs) with superior elongation at break and low residual strains as compared to conventional TPEs.     

Synthesis and crystallization behavior study of syndiotactic polystyrene‐g‐isotactic polypropylene (sPS‐g‐iPP) graft copolymers

Based on coordination polymerization mechanism only, novel stereoregular graft copolymers with syndiotactic polystyrene main chain and isotactic polypropylene side chain (sPS‐g‐iPP) were synthesized via two steps of catalytic reactions. First, a chain transfer reaction was initiated by a chain transfer complex composed of a styrene derivative, 1,2‐bis(4‐vinylphenyl)ethane, and hydrogen in propylene polymerization mediated by rac‐Me₂Si[2‐Me‐4‐Ph(Ind)]₂ZrCl₂ and MAO, which gave iPP macromonomer bearing a terminal styryl group (iPP‐t‐St). Then the iPP‐t‐St macromonomers of varied molecular mass were engaged in syndiospecific styrene polymerization over a typical mono‐titanocene catalyst (CpTiCl₃/MAO) under different conditions to produce sPS‐g‐iPP graft copolymers of varied structure. With an effective purification process, well‐defined sPS‐g‐iPP copolymers were obtained, which were then subjected to differential scanning calorimetry (DSC) and polarized optical micrograph (POM) studies. The graft copolymers were generally found with dual melting and crystallization temperatures, which were ascribable respectively to the sPS backbone and iPP graft. However, it was revealed that the two segments displayed largely different melting and crystallization behaviors than sPS homopolymer and the precursory iPP‐t‐St macromonomer. Consequently, the graft copolymer exhibited much distinctive crystalline morphologies when compared with their individual components. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Structure and mechanical properties controlling of elastomer modified polypropylene by compounded β/α nucleating agents

Previous work showed that there was a synergistic effect of nucleating agent (NA) and elastomer in improving the fracture resistance of isotactic polypropylene (PP), relating to the formation of large amounts of β‐PP (β‐NA nucleated system) or the decrease of the spherulites diameters of α‐PP (α‐NA nucleated system). To find the direct relation between the synergistic efficiency of NA/elastomer and the microstructures of the materials, in this work, the ethylene‐propylene‐diene terpolymer (EPDM) modified PP blends with compounded NAs (β/α) were adopted and the changes of the microstructure and mechanical properties were investigated comparatively. The results showed that, with the adjustment of the mass fraction of compounded NAs, the microstructures of PP matrix including supermolecular structure and the relative fraction of β‐PP (K_β) change accordingly. Specifically, the K_β of β‐PP was successfully adjusted in the wide range of 0–78.9%. Consequently, the stiffness and the fracture resistance of the PP/EPDM blends were easily controlled in different degrees. It is believed that this work could provide a guide map for the design and preparation of certain polymer blends satisfying certain requirement. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

步进扫描差示扫描量热法研究不同链结构的聚乙烯类聚烯烃热力学特性

采用步进扫描差示扫描量热法研究了几种具有不同链结构的聚乙烯类聚烯烃的热力学性质.结果表明,不同链结构的聚烯烃在热力学平衡熔融态下,其绝对比热容的温度依赖性在实验误差范围内几乎相同;而无论链结构的变化如何,在极低温度下稳定结晶态的热容也非常接近.但在熔融温度范围内,比热容对不同聚烯烃的链结构非常敏感,这是由于在远低于聚烯烃主熔化峰温度范围内,聚乙烯晶体结构中的不同支链的影响.在时间-热流的步进扫描曲线中,具有长支链结构的聚烯烃表现出独特的熔融-再结晶行为,这可能是由于交联点之间较长的受约束链段的运动在熔融过程中得到释放并重排所致.     

Effect of Cyclic Deformation on Magnetorheological Elastomers

Fatigue properties of magnetorheological elastomer (MRE) samples were investigated based on cis-polybutadiene rubber by using a fatigue test machine. Three MRE samples with iron particles mass fraction of 60%, 70%, and 80% were fabricated, and their properties dependence of three strain amplitudes (50%, 75%, and 100%) were measured. The absolute magnetorheological (MR) effect, storage modulus, and loss modulus of MRE samples after fatigue were evaluated by a modified dynamic mechanical analyzer. The results revealed that MR effect, storage modulus, and loss modulus of MREs containing 80% iron particles depended strongly on the strain amplitudes and the number of cycles, while storage mod-ulus and loss modulus of MREs containing 70% iron particles also depended on the strain amplitudes and the number of cycles but not as strongly as sample which contains 80% iron particles, but the properties of MREs containing 60% iron particles after cyclic deforma-tion were almost independent of the fatigued conditions. In order to investigate the fatigue mechanism of MREs, the sample was carried out with a quasi-static tensile testing and its surface morphology during testing was observed in situ by scanning electron microscopy.     

叶立德活性聚合制备基于聚亚甲基的大分子单体

利用叶立德活性聚合方法制备了两种基于聚亚甲基的大分子单体. 其中一种是以叶立德活性聚合制备的主链链端含有羟基的聚亚甲基(PM-OH)为原料, 通过链端羟基的基团转换, 得到链端含有甲基丙烯酸酯基的大分子单体. 另一种则是以硼烷-四氢呋喃(BH₃-THF)和二乙烯基苯反应得到的三烷基硼中间体为催化剂和引发剂, 然后进行叶立德活性聚合, 再经过二水合氧化三甲胺(TAO)的氧化, 最终得到基于聚亚甲基的一端含有羟基另一端含有苯乙烯基的大分子单体. 通过高温核磁氢谱、傅立叶红外光谱和高温凝胶色谱法表征了这两种大分子单体的链结构和分子量及其分布.