固体1H-NMR表征玻璃态高分子链的缠结、互穿及链间邻近度

系统回顾了缠结定义的演化及对其表征的各种方法,比较了这些方法的特点和不足.在以往研究的基础上,发展了一套在分子尺度上表征玻璃态高分子链互穿的方法.该方法结合高速魔角和偶极滤波,用固体1H-NMR探测互穿区域的质子信号,表征了玻璃态聚苯乙烯的链互穿程度.该方法在0.5 nm尺度范围内测定了分子链间的距离,且与以往方法相比,该方法具有耗时短、需要样品量少、灵敏度和信噪比高等优点.     

Two-component interpenetrating polymer networks (IPNs) from polyurethanes and epoxies. I. Studies on full IPN,pseudo-IPN,and graft polymer alloys of polyurethanes and epoxies

In this article we review the synthesis and morphology and the physical and mechanical properties of two-component interpenetrating polymer networks (IPNs) from polyurethane and epoxy polymers; the corresponding pseudo-IPNs and grafted IPNs are also discussed. A comparison was made of full IPNs, pseudo-IPNs, grafted IPNs, and related homopolymers by examining their mechanical properties, mechanical spectra, and electron microscopy on an investigation of the effects of interpenetration or permanent entanglement in the IPN and related systems. This interpenetration has resulted in improved compatibility between the two polymer systems and has caused a decrease in the degree of phase separation. An observed shift in the dynamic glass transition temperatures (T_gs) of the two components which yielded a single IPN T_g further substantiates our results.     

链缠结对高聚物热转变行为的影响

用冷冻升华方法,由等规聚苯乙烯、聚环氧乙烷的稀溶液制备单链、寡链附聚粒子．附聚粒子的热分析表明,冷结晶温度降低、结晶速度加快、晶体增厚明显．这些结果是因为附聚粒子没有或有很少链间缠结．附聚粒子形成较小尺寸的晶体,因而熔点较低,相应的热结晶温度移向低温．在平衡熔点以上放置短时间,链相互贯穿、缠结,又回复到本体的熔融、结晶行为     

低苯乙烯含量的丁二烯-苯乙烯共聚物的激基缔合物荧光研究

本文报导一种低苯乙烯含量(5％,Wt.)的丁二烯-苯乙烯共聚物,经~1H NMR证明其分子链上不存在相邻苯乙烯单元。荧光光谱结果表明,它在良溶剂(二氯乙烷)的稀溶液状态下只呈现单分子荧光。从良溶剂-θ溶剂(二氯乙烷-甲醇体系)及稀溶液-浓溶液-固体之荧光光谱的变化,证明形成了链内非近邻生色团之间和链间生色团之间的激基缔合物(Excimer)。从固体与θ溶剂的激基缔合物荧光的比较,还可区分链内非近邻和链间苯环形成激基缔合物对荧光强度的贡献。这一结果对阐明高分子链内非近邻和链间激基缔合作用提供了新的证据,并有助于了解高聚物本体中相互穿透、相互缠结的无规线团的形态。     

聚环氧氯丙烷聚氨酯／聚甲基丙烯酸甲酯互穿网络聚合物的相容性与力学性能

用同步法合成了聚环氧氯丙烷聚氨酯／聚甲基丙烯酸甲酯互穿网络聚合物［ＰＵ（ＰＥＣＨ）／ＰＭＭＡＩＰＮ］，调节ＩＰＮ中两组分组成比制备出由完全弹性体、增强弹性体、增韧塑料到脆性塑料多种高聚物合金材料．用ＤＳＣ、动态力学谱、ＴＥＭ对ＩＰＮ的研究结果表明，ＰＵ（ＰＥＣＨ）／ＰＭＭＡＩＰＮ的两组分是完全相容的；同时对各种组成比的ＩＰＮ材料进行力学性能测试，用相容性ＩＰＮ中互穿、缠结结构解释其力学行为，并用ＳＥＭ对断面形貌进行了观察解释．     

Synthesis of new amphiphilic and lypophilic polymer networks containing 2‐methyl‐ and 2‐nonyl‐2‐oxazoline by the macroinitiator method

New amphiphilic and lypophilic polymer networks were obtained by the copolymerization of 2‐methyl‐2‐oxazoline (MeOXA), and/or 2‐nonyl‐2‐oxazoline (NoOXA) and 2,2′‐tetramethylenebis(2‐oxazoline) (BisOXA), respectively, initiating the copolymerization by random copolymers of chloromethylstyrene and methyl methacrylate or of chloromethylstyrene and styrene (macroinitiator method). Potassium iodide was used as an activator agent and the reaction was carried out in benzonitrile at 110 °C. In general, the polymer gels were obtained with a yield of 62 to 88%. The networks were characterized by high‐resolution magic angle spinning (HRMAS) NMR spectroscopy and by its absorption of polar and nonpolar solvents. In the case of amphiphilic polymer networks, the absorption of solvents depends on the molar ratio of 2‐methyl‐ to 2‐nonyl‐2‐oxazoline inside the polymer network favoring the absorption of polar solvents with a higher content of 2‐methyl‐2‐oxazoline. These gels showed a maximal swelling degree of 13 mL of water, 20 mL of methanol, and 13 mL of chloroform, respectively, per g of polymer. The lypophilic polymer networks containing only 2‐nonyl‐2‐oxazoline showed a maximal swelling degree of 8 mL of toluene, 14 mL of chloroform, and 2 mL of methanol, respectively, per g of the lypophilic network. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 122–128, 2005     

Mesoscale simulations of the behavior of charged polymer brushes under normal compression and lateral shear forces

Dissipative particle dynamics (DPD) was used to investigate the behavior of two opposing end-grafted charged polymer brushes in aqueous media under normal compression and lateral shear. The effect of polymer molecular weight, degree of ionization, grafting density, ionic strength, and compression on the polymer conformation and the resulting shear force between the opposing polymer layers were investigated. The simulations were carried out for the poly(tert-butyl methacrylate)-block-poly(sodium sulfonate glycidyl methacrylate) copolymer, referred as PtBMA-b-PGMAS, end-attached to a hydrophobic surface for comparison with previous experimental data. Mutual interpenetration of the opposing end-grafted chains upon compression is negligible for highly charged polymer brushes for compression ratios ranging from 2.5 to 0.25. Under electrostatic screening effects or for weakly charged polymer brushes, a significant mutual interpenetration was measured. The variation of interpenetration thickness with separation distance, grafting density, and polymer size follows the same scaling law as the one observed for two opposing grafted neutral brushes in good solvent. However, compression between two opposing charged brushes results in less interpenetration relative to neutral brushes when considering equivalent grafting density and molecular weight. The friction coefficient between two opposing polymer-coated surfaces sliding past each other is shown to be directly correlated with the interpenetration thickness and more specifically to the number of polymer segments within the interpenetration layer.     

穿插程度对高分子链结晶初始阶段的影响

用分子动力学方法模拟了具有不同穿插程度的寡链凝聚体系结晶初始阶段的有序化过程. 链间穿插程度通过径向分布函数的统计进行表征. 模拟计算结果表明, 链间的穿插程度对体系的有序化过程具有明显的影响, 穿插程度越小的体系有序化越快, 形成的有序结构也更完整. 与实验结果的比较表明, 在聚合物粒子结晶的初始阶段, 体系由穿插引起的缠结就已经起到了作用.     

辐射交联顺-1,4-聚丁二烯的网络结构特性和力学性能

本文根据Flory的溶胀理论和橡胶弹性理论,考察了顺-1 4-聚丁二烯辐射交联产物的化学网络和物理缠结网络结构特性及其对固体力学性能的影响。结果表明,交联产物的物理缠结网络密度远远大于化学交联网络密度。随着辐照剂量的增大,化学交联密度增高,物理缠结数下降。探讨了交联、缠结密度与Mooney-Rivlin方程的常数项C_1和C_2的关系。C_1来自化学交联网络的贡献;C_2来自物理缠结的贡献。物理缠结网络主要贡献于交联物体在小形变下的起始弹性模量G_0;化学交联网络则主要贡献于交联物体在大形变下的非线性弹性,即断裂强度(?)_B。     

Heating caused by radiofrequency irradiation and sample rotation in 13C magic angle spinning NMR studies of lipid membranes

Application of rapid sample rotation and radiofrequency irradiation in magic angle spinning (MAS) NMR of lipid bilayers can significantly increase the sample temperature. In this work, we studied the extent of heating during the acquisition of 1H-decoupled 13C MAS spectra of hydrated dimyristoylphosphatidylcholine (DMPC) in the L(alpha) phase. First, we describe a simple procedure for determining the increase in temperature by observing the shift of the 1H water signal. The method is then used to identify and assess the various factors that contribute to the sample heating. The important factors discussed in this paper include: (i) the spinning speed, (ii) the variable-temperature gas pressure, (iii) the rotor geometry, (iv) the power, duration and frequency of the radiofrequency irradiation and (v) the hydration level. A comparison of different heteronuclear decoupling schemes in terms of their ability to produce highly resolved 13C spectra of DMPC is also reported.     

A study of molecular mobility and relaxation properties of epoxy-allyl interpenetrating polymer networks with a high degree of interpenetration

Features of the formation of the epoxy-allyl polymers are considered during simultaneous and consecutive curing of epoxy and allyl polymers. Study of their molecular mobility and relaxation properties shows the high interpenetration degree of the epoxy-allyl interpenetrating polymer networks.     

Solid‐state NMR characterization of oxygen sites in organically modified aluminosilicate xerogels

Solid‐state NMR characterization of hybrid aluminosilicate xerogels, by ¹⁷O magic angle spinning (MAS) and triple quantum magic angle spinning (MQMAS) techniques, evidences Si—O—Si and Si—O—Al oxygen sites, spectrally separated in MQMAS experiments. Inversion of the MQMAS spectra allows the measurement of quadrupolar parameters, isotropic chemical shifts, distribution of chemical shift and discussion of the mobility of the structural units. Copyright © 2003 John Wiley & Sons, Ltd.     

Interpenetration of polystyrene chains in bulk polymer

Polystyrenes lightly substituted with either tertiary amine groups or nitrophenol groups have been allowed to interact in concentrated t-butylbenzene solution and in bulk polymer. Above the glass transition temperature a temperature dependent equilibrium is achieved in the bulk polymer between the two substituents and the amine salt of the phenol. The degree of association found is considerably greater in the bulk polymer than in solution. The results show that much interpenetration of the polymer occurs, and the results are discussed in terms of models of the bulk amorphous state of the polymer.     

A Langevin dynamics simulation study of the tribology of polymer loop brushes

The tribology of surfaces modified with doubly bound polymer chains (loops) has been investigated in good solvent conditions using Langevin dynamics simulations. The density profiles, brush interpenetration, chain inclination, normal forces, and shear forces for two flat substrates modified by doubly bound bead-necklace polymers and equivalent singly bound polymers (twice as many polymer chains of 12 the molecular weight of the loop chains) were determined and compared as a function of surface separation, grafting density, and shear velocity. The doubly bound polymer layers showed less interpenetration with decreasing separation than the equivalent singly bound layers. Surprisingly, this difference in interpenetration between doubly bound polymer and singly bound polymer did not result in decreased friction at high shear velocity possibly due to the decreased ability of the doubly bound chains to deform in response to the applied shear. However, at lower shear velocity, where deformation of the chains in the flow direction is less pronounced and the difference in interpenetration is greater between the doubly bound and singly bound chains, some reduction in friction was observed.     

以改进的荧光非辐射能量转移法研究高分子共混物

荧光非辐射能量转移(NRET)法可灵敏地反映出在几纳米尺度上分子相互作用的信息。这一性质已广泛用于高分子共混物相容性的研究。通常的NRET方法是通过测定两种聚合物链的相互接近的程度得到有关相容性的信息。但相区的大小与形态都会影响能量转移的效率,且需对共混物中的组成聚合物分别以荧光能量给体和受体进行标记,与此不同,本     

Hydrogen-bonded polymer multilayers probed by neutron reflectivity

We present a neutron reflectivity study of the internal structure of multilayers made of a weak polyelectrolyte and a neutral component where interactions between adjacent layers are controlled by hydrogen-bonding. We found the degree of interpenetration of polymer layers expressed as the interlayer roughness to be strongly correlated with the strength of intermolecular interactions between the adjacent layers. In addition, polymer layers become more diffuse with a distance from the substrate. Our results demonstrate that hydrogen-bonded films exhibit a close correlation between their structure and properties, which is essential for various applications.     

On some mechanical effects in glassy polymers attributed to chain entanglements

The important role of the entanglements in the deformation of high-molecular-weight glassy polymers is demonstrated by two phenomena: the build-up of material resistance in polymethylmethacrylate after chain interpenetration and the intrinsic crazing of polycarbonate which is observed when the entanglement network reaches its limits of extension.Dedicated to Prof. Dr. F. H. Müller.     

Curvature effects upon interactions of polymer-grafted nanoparticles in chemically identical polymer matrices

We study the interactions between polymer-grafted nanoparticles immersed in a chemically identical polymer melt using a numerical implementation of polymer mean-field theory. We focus on the interpenetration width between the grafted and free chains and its relationship to the polymer-mediated interparticle interactions. To this end, we quantify the interpenetration width as a function of particle curvature, grafting density, and the relative molecular weights of the grafted and free chains. We show the onset of wetting and dewetting as a function of these quantities and explain our results through simple scaling arguments to include the effects of curvature. Subsequently, we show that the interparticle potentials correlate quantitatively with the trends displayed by the interpenetration widths.     

环氧／环氧丙烯酸酯的光交联和动态力学性能

用硬度法研究了环氧／环氧丙烯酸酯混杂体系中以硫翁盐引发光交联时，组成对光交联的影响；安息香二甲醚能促进混杂体系的光交联；动态力学性能的测定表明该体系是一相容性互网络体系；组成对体系的相容性，交联密度、互穿程度均有影响。     

Centrifugally spun poly(ethylene oxide) fibers rival the properties of electrospun fibers

Centrifugal force spinning (CFS), also known as centrifugal spinning, forcespinning, or rotary jet spinning, provides considerably higher production rates than electrospinning (ES), but the more widespread use of CFS as an alternative depends on the ability to produce fibers with robust thermal and mechanical properties. Here, we report the CFS of poly(ethylene oxide) (PEO) fibers made using a spinning dope formulated with acetonitrile (AcN) as the volatile solvent, and we describe the thermal and mechanical properties of the centrifugally-spun fibers. Even though the formation, diameter, and morphology of electrospun and centrifugally-spun PEO fibers are relatively well-studied, the article presents three crucial contributions: the pioneering use of PEO solutions in AcN as spinning dope, characterization of crystallinity and mechanical properties of the centrifugally-spun PEO fibers, and a comparison with the corresponding properties of electrospun fibers. We find that fiber formation occurrs for the chosen CFS conditions if polymer concentration exceeds the entanglement concentration, determined from the measured specific viscosity. Most significantly, the centrifugally spun PEO fibers display crystallinity, modulus, elongation-at-break, and fiber diameter that rival the properties of electrospun PEO fibers reported in the literature.