Solvent-Polymer Interaction. II. Measurements of Liquid Solvent Molecules Associating with Polymer Sites and of Their Transport Behavior in Polymer Membrane by Thermogravimetry,GLC, and Mass Spectrometry

The measurement of sorption and diffusion behavior of liquid ethanol and water solvent mixtures in polyurethane membrane were made simultaneously by thermogravimetry. The individual amounts of sorbed water and ethanol in the polymer membrane were estimated by thermogravimetry and differentiated by mass spectrometry. In addition, from a single dynamic thermogravimetric experiment the activation energy for solvent molecules desorbing from the polymer membrane was also determined. The thermodynamic activity of ethanol vapor in equilibrium with the ethanol-water-polyurethane system was determined by gas-liquid chromatography. The clustering functions, the mean numbers of solvent molecules in the clusters, and those associating with polymer sites were evaluated by applying simplified mathematical derivatives using the experimentally determined values of activity and volume fraction of solvent molecules. It was found that at lower ethanol concentration the tendency for ethanol molecules to cluster together is high. At higher ethanol activity, ethanol-polymer site interactions predominantly occurred.

Similar results were observed for ethanol-water molecules. However, water molecules in this particular system did not exhibit a self-associating tendency nor interact with the polymer sites. It was concluded that the Zimm-Lundberg clustering theory can be adequately applied to the interpretation of sorption and diffusion behavior of liquid ethanol-water mixtures in the polymer membrane.     

Polyurethane Ionomers from Cycloaliphatic Diisocyanate and Polytetramethylene Glycol

Abstract

Segmented polyurethane (PU) ionomers were prepared from cycloaliphatic diisocyanate [methylene bis(4-cyclohexyl isocyanate) (H₁₂MDI) and isophoron diisocyanate (IPDI)] and polytetramethylene glycol (PTMG) by using an anionic-type chain extender, viz., dimethylol propionic acid (DMPA). The effect of ionic content and butanediol (BD) on the state of dispersion and physical properties of emulsion-cast film was determined using Autosizer, transmission electron microscopy (TEM), Instron, and Rheovibron. With increased incorporations of DMPA in PU, particle size of emulsion decreased asymptotically, tensile modulus and strength increased, and the glass transition temperature (T _g) moved toward the higher temperature. On the other hand, with increased incorporation of BD in PU, particle size of emulsion, tensile modulus, and strength of the emulsion cast film increased, and the major transition of soft segment moved toward higher temperature. With regard to the structural effect of the isocyanate, H₁₂MDI gave finer dispersion and better mechanical properties over IPDI.     

铁磁性高分子——聚丁二炔衍生物的合成与磁性研究

本文报道了三种类型丁二炔的合成:R_1-C≡C-C≡C-R_2,a:R_1=R_2=自由基;b:R_1≠R_2 R_1或R_2为自由基;c:R_1=R_1≠自由基.利用热聚合方法制得三种类型的聚丁二炔,并对它们的磁行为进行了研究,对聚丁二炔衍生物的磁性来源进行了讨论,证明了聚丁二炔衍生物中单独全共轭链自旋体系和单独的自由基侧链自旋体系均不产生铁磁性,其磁性来源于聚丁二炔衍生物中氮氧自由基和共轭主链的共同作用.     

聚二乙炴电子能带结构的研究

聚二乙炔(polydiacetylenes)具有平面的全共轭主链,并可被制备成宏观大小的单晶,因而是研究聚合物物理、化学性质的理想模型.它的物理、化学性质,特别是作为导电材料的导电机理与其价带及导带的结构密切相关.通过改变聚二乙炔的侧基可以对其主链几何结构及电子能带结构产生影响,进而改变其物理化学性质.可能是考     

聚二乙炔链振动谱的研究

将聚二乙炔主链简化为有限的一维复式碳原子链,利用经典的晶格动力学方法研究了其色散关系.聚二乙炔链色散关系曲线由一支声学模和三支光学模组成,它们在波矢为零处及Brillouin zone(BZ)边界处拉开了间隙,弹性力常数的变化将显著地改变带宽和能隙.     

Theoretical Investigation on the Topochemical Polymerization of Diacetylenes

Abstract

The solid-state polymerization of diacetylenes (MDA-PBT-PDA) is studied with a concerted reaction model and the calculation method of EHMO-ASED and EHCO-ASED, where MDA = crystalline molecular diacetylenes, PBT = polybutatrienes, and PDA = polydiacetylenes. As the reaction goes on, the symmetry of frontier orbitals inverts at state PBT, HOCO from C ₂-antisymmetry to C ₂-symmetry and LUCO from C ₂-symmetry to C ₂-antisymmetry, which means completion of the 1,4-addition. Two necessary conditions must be satisfied for the reaction to take place: 1) the geometric parameters must undergo a series of concerted changes to make the conformation suitable for the intermolecular 1,4-addition, which should overcome an energy barrier E_b ; 2) the symmetry match between the frontier crystal orbitals of the reactant and the product must be satisfied-electrons of the reactant should be excited from HOCO (C ₂-antisymmetry) into LUCO (C ₂-symmetry), which faces an energy gap E _g. At state MDA, there is E _g(MDA) ≈ 5.6 eV. If MDA and PDA are analyzed according to Woodward-Hoffmann's rules, this reaction would be considered photochemically allowed but thermochemically forbidden. It has been shown that the E _g gradually decreases along the reaction coordinate from state MDA to PBT. At state PBT there is E _g(PBT) ≤ 0.1 eV, and the electrons of the reactant can be easily excited there. Since E_b ≤ 1.0 eV is not very large and E_g (PBT) ≤ 0.1 eV is very small, the two necessary conditions mentioned above can be satisfied thermally. Therefore, thermal polymerization can take place smoothly. By this pathway the apparent activation energy of the reaction will be E_a ≤ 1.0 eV, which is consistent with the activation energies of the polymerizations of diacetylenes in the literature.     

Field-Induced Order in Nematic Liquid Crystals

The effect of an external magnetic field on the orientational order of a nematic liquid crystal has been examined using both Landau-de Gennes and Maier-Saupe theories. In the Maier-Saupe approach a rotationally invariant form of the pseudo-potential is introduced, which in the absence of an external field leads to three degenerate isomorphic solutions for the order parameter, corresponding to alignment along three principal axes; a similar result is obtainable from the Landau-de Gennes theory. Application of a magnetic field lifts the degeneracy of these solutions, and for materials having a positive diamagnetic susceptibility anisotropy, the uniaxial solution with alignment along the field direction is always energetically favorable. For materials with a negative susceptibility anisotropy, a biaxial solution minimizes the free energy at low temperatures, but on increasing the temperature there is a transition from a biaxial phase to an uniaxial phase. The field dependence of the transition temperatures is evaluated, and for positive materials there is a critical field, corresponding to a second order transition above which the nematic and isotropic phases are indistinguishable. A contrasting behavior is predicted for negative materials, and above a certain critical field the biaxial/uniaxial transition changes from first order to second order. For weakly ordered systems it is shown that the Landau-de Gennes expression for the free energy is identical to that obtained from the Maier-Saupe theory. However, for more ordered systems, the results of the two approaches differ, and in particular the Maier-Saupe theory predicts a susceptibility divergence temperature T* which increases with applied field, in agreement with recent experiments.     

热致可逆变色的聚二炔／稀土离子纳米复合物

将Dy^＋或Sm^＋掺杂到具有层状结构的10,12-二十五碳二炔酸（PCDA）纳米粒子中,得到二炔酸／稀土离子（PCDA-RE）纳米复合物．随后在稍微高于二炔酸熔点的温度下对PCDA—RE纳米复合物进行退火处理,退火后的PCDA—RE纳米复合物发生拓扑聚合反应得到聚二炔酸／稀土离子（PDA-RE）纳米复合物．虽然纯聚二炔酸的热致变色过程是不可逆的,但是PDA—Sm纳米复合物和PDA-Dy纳米复合物分别具有不完全和完全热致可逆变色的性能．研究表明,PDA-RE纳米复合物的层间距为5,4nm,比纯聚二炔酸的层间距（4．7nm）要大．对于PDA—RE纳米复合物,稀土离子和聚二炔酸之间的强相互作用是纳米复合物实现大部分或完全可逆变色的原因．同时退火处理对实现聚二炔酸可逆变色非常重要,因为退火处理消除了材料结构中的所有缺陷,最终促使材料具有热致可逆变色性能．     

Order-Disorder Transition of Carboxyl Terminated Chains in Polydiacetylenes Vesicles Probed by Second Harmonic Generation and Two-Photon Fluorescence

To understand and control the interfacial properties of polydiacetylenes (PDAs) vesicles with π-conjugated backbone is very important for their colorimetric sensing of chemical and biological targets. In this work, we adopted 10, 12-pentacosadiynoic acid (PCDA) as the model molecule to prepare PDAs vesicles in aqueous solution with different forms (from monomer to blue-to-purple-to-red phase) by controlling the UV irradiation dose. The variations of the interfacial conformation of PDAs vesicles during chromatic transitions were inspected by the adsorption behaviors of probe molecules (4-(4-diethylaminostyry)-1-methylpyridinium iodide, D289) on vesicle surface with surface-specific second harmonic generation (SHG) and zeta potential measurements. Resonant SHG signal from D289 adsorbed on vesicle surface attenuated sharply, and the adsorption free energy as well as the corresponding two-photon fluorescence signal decreased slightly in chromatic transitions. While, the change in the surface density of the adsorbed D289 molecules for PDAs vesicles with different forms was relatively small as estimated from zeta potential measurements. The attenuation of the SHG intensity was thus attributed to the overall order-disorder transition and the changed orientation of D289 molecules caused by the gradual distortion of carboxyl head group driven by backbone perturbation.     

热致可逆变色的聚二炔/稀土离子纳米复合物

将Dy⁺或Sm⁺掺杂到具有层状结构的10,12-二十五碳二炔酸(PCDA)纳米粒子中,得到二炔酸/稀土离子(PCDA-RE)纳米复合物．随后在稍微高于二炔酸熔点的温度下对PCDA-RE纳米复合物进行退火处理,退火后的PCDA-RE纳米复合物发生拓扑聚合反应得到聚二炔酸/稀土离子(PDA-RE)纳米复合物．虽然纯聚二炔酸的热致变色过程是不可逆的,但是PDA-Sm纳米复合物和PDA-Dy纳米复合物分别具有不完全和完全热致可逆变色的性能．研究表明,PDA-RE纳米复合