Preparation,Morphology and Properties of Poly(Trimethylene Terephthalate)/Thermoplastic Polyester Elastomer Blends

Poly(trimethylene terephthalate)(PTT)/thermoplastic polyester elastomer (TPEE) blends were prepared and their miscibility, crystallization and melting behaviors, phase morphology, dynamic mechanical behavior, rheology behavior, spherulites morphology, and mechanical properties were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), parallel-plate rotational rheometry, polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD), universal tensile tester and impact tester, respectively. The results suggested that PTT and TPEE were partially miscible in the amorphous state, the TPEE rich phase was dispersed uniformly in the solid matrix with a size smaller than 2 μm, and the glass transition temperatures of the blends decreased with increasing TPEE content. The TPEE component had a good effect on toughening the PTT without depressing the tensile strength. The blends had improved melt viscosities for processing. When the blends crystallized from the melt state, the onset crystallization temperature decreased, but they had a faster crystallization rate at low temperatures. All the blends’ melts exhibited a predominantly viscous behavior rather than an elastic behavior, but the melt elasticity increased with increasing TPEE content. When the blends crystallized from the melt, the PTT component could form spherulites but their morphology was imperfect with a small size. The blends had larger storage moduli at low temperatures than that of pure PTT.     

Synthesis and characterization of in-chain silyl-hydride functional SBR and self-crosslinking elastomer

Functional in-chain silyl-hydride(Si-H) SBR copolymers of 4-vinyiphenyldimethylsilanol(VPDMS) and butadiene were synthesized by living anionic polymerization,in which active group Si-H was not lost and its content was controllable. Corresponding self-crosslinking elastomers were obtained by hydrosilation of Si-H group with vinyl bonds in chain.The copolymers and elastomers were characterized by ~1H NMR,size exclusion chromatography(SEC),Fourier transform infrared (FTIR) spectroscopy,differential scanning calorimetry(DSC),and thermogravimetry analysis(TGA) techniques.     

Stress‐Induced Melting of Crystals in Natural Rubber: a New Way to Tailor the Transition Temperature of Shape Memory Polymers

Lightly cross‐linked natural rubber (NR, cis‐1,4‐polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain‐induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain‐stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature T_trig(σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal‐stabilized SMP after programming.     

多个磁流变弹性体自调谐式吸振器的联合控制研究

遗传算法是一种自适应、启发式、全局优化的搜索算法,在结构振动控制等复杂控制领域得到了广泛的应用,本文针对磁流变弹性体自调谐式吸振器难以建立准确的控制模型的特点,通过改进基本遗传算法,设计和实现了一种同时控制多个吸振器的联合控制算法,该方法在协调控制时,根据多个吸振器协调控制对控制量的要求采用指定位交叉产生新个体,与通过随机位交叉产生的新个体相比,这样能以较大的概率产生更健壮的新个体,从而使算法更快收敛.将该算法应用到两个吸振器联合控制的实验系统中,在吸振器移频范围内,被减振系统各观测点均有较好的减振效果,当吸振器与主系统质量比为1∶19.8时,减振效果最高约12dB,主被动减振效果之差最佳时达7dB.     

Helix coil mixing in twist-storing polymers

Twist-storing polymers respond with elastic energy penalty to coherent or random twisting along the local chain axis away from its equilibrium, which can be straight (as in “ribbons”) or helical (as in DNA and other biopolymers). Here we study the equilibrium conformation of such polymers, focusing on the thermodynamic balance between twist and writhe, resulting from the competition between the random coil entropy and the potential energy stored in superhelical portions of the polymer chain. Two macroscopic variables characterise such a chain, the end-to-end distance R and the link number Lk, which is a topological invariant of a given polymer with clamped ends. We find that with increasing link number Lk, the chain accommodates its excess twist in growing plectonemes, unless forced out of this state by stretching its end-to-end distance R. We calculate the force-extension relation, which exhibits crossovers between different deformation regimes. Received 16 November 2000 and Received in final form 6 February 2001     

Heterogeneous dynamics at the glass transition in van der Waals liquids, in the bulk and in thin films

It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous dynamics close to T _g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T _g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T _g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation. Received 21 March 2000 and Received in final form 4 December 2000     

Polyurethanes containing sulfur. III. New thermoplastic HDI-based segmented polyurethanes with diphenylmethane unit in their structure

Three series of new thermoplastic, high molecular weight, segmented thiopolyurethanes were synthesized by a one-step melt polymerization from newly obtained thiodiols, including bis[4-(2-hydroxyethyl)thiomethylphenyl]methane, bis[4-(3-hydroxypropyl)thiomethylphenyl]methane, and bis[4-(6-hydroxyhexyl)thiomethylphenyl]methane (BHHM), as chain extenders; hexamethylene diisocyanate; and 20–80 mol % poly(oxytetramethylene) glycol (PTMG; number-average molecular weight = 1000) as the soft segment. Solution polymerization with the chain extender BHHM gave considerably lower molecular weight polymers. The structures of all the polyurethanes were determined with Fourier transform infrared and X-ray diffraction analysis. The thermal properties of the polyurethanes were examined with differential scanning calorimetry and thermogravimetric analysis. Shore A/D hardness and tensile properties were also determined. All the polyurethanes showed partially crystalline structures; those obtained with 40–80 mol % PTMG were elastomers. An increase in the PTMG content decreased hardness, modulus of elasticity, and tensile strength, whereas elongation at break increased. BHHM-based polyurethanes obtained in the melt showed the best tensile properties. The polyurethanes exhibited definite glass transitions (−70 to −59 °C) that were nearly independent of the hard-segment content up to about 50 wt % (40–80 mol % PTMG), indicating the existence of mainly microphase-separated soft and hard segments. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1733–1742, 2001     

热塑性聚氨酯弹性体中的氢键作用──动态力学分析

采用动态力学分析方法研究了一系列由聚四氢呋喃(M_n=2000)、4,4-二苯基甲烷二异氰酸酯以及N-甲基二乙醇胺、1,4-丁二醇和1,2-丙二胺三种不同的扩链剂合成的TPU中的氢键作用.发现这种氢键作用符合Arrhenius型的温度依赖性.从弹性模量-温度关系曲线上估算出氢键解离活化能和物理交联密度     

NMR Reveals Non‐Distributed and Uniform Character of Network Chain Dynamics

Results of different NMR investigations of elastomers are reviewed with respect to their significance for statistical models of rubber elasticity. In contrast to earlier work based on lineshape analysis and relaxometry, results of recent multiple‐quantum experiments indicate that the NMR‐detected dynamic chain order parameter, which reflects the conformational space of individual monomer units at which the signal is detected locally, is a rather narrowly distributed quantity. Constraints to the dynamics and the conformations of a network chain thus act uniformly and appear as a dynamic average over chains of different length and with different end‐to‐end separations. All our findings are in good agreement with large‐scale computer simulations. Anomalies on swelling such as chain desinterspersion at the early stages and the appearance of heterogeneities, are also discussed.

     

Monte Carlo Simulations on Nanoparticles in Elastomers. Effects of the Particles on the Dimensions of the Polymer Chains and the Mechanical Properties of the Networks

Summary: Reinforcement of elastomers is modeled using Monte Carlo simulations on rotational isomeric state chains, to characterize their spatial configurations in the vicinity of filler particles. The resulting filler-perturbed distributions of the chain end-to-end distances are in agreement with experimental results gotten by neutron scattering. The use of these distributions in a standard molecular theory of rubberlike elasticity produces stress-strain isotherms for elongation that are consistent with available experimental results.