Probing polymer/polymer interfaces

Infrared-visible sum frequency generation spectroscopy (SFG) has been used to study the interface between poly(vinyl-N-octadecylcarbamate-co-vinyl acetate) (Comb) and deuterated or hydrogenated polystyrene (dPS or hPS) films. Strong methyl symmetric and Fermi resonance bands associated with the alkyl side chains of the Comb polymer are observed in the SFG spectra. In addition, for Comb/hPS spectra, symmetric and asymmetric vibration modes of phenyl groups are observed. The presence of asymmetric modes indicates the phenyl rings are tilted with respect to the interface normal.     

Uniform polymer in synthetic polymer chemistry

The preparation of uniform polymers and their use in fundamental polymer chemistry are reviewed. A typical method of preparation is a combination of living polymerization and supercritical fluid chromatography separation. Synthetic uniform polymers allow us to solve ambiguous problems in polymer chemistry due to molecular weight distribution and are of significant importance for studies on structure–property relationships. A close inspection of an isotactic uniform chloral oligomer with a symmetrical chemical structure reveals that oligomers are the first examples of stable atropisomers of aldehyde oligomers and that their chiroptical properties are due only to their helical geometries. A molecular-level understanding of the mechanism and stoichiometry of the association process of polymer molecules is possible only with uniform polymers, and stereocomplex formation between isotactic and syndiotactic poly(methyl methacrylate)s in acetone has vigorously been studied by size exclusion chromatography (SEC) and NMR. End-functionalized uniform polymers have enabled us to prepare uniform polymer architectures, such as block, graft, comb, and star polymers. A uniform stereoblock poly(methyl methacrylate) with an isotactic (methyl methacrylate)₄₆-syndiotactic (methyl methacrylate)₄₆ structure shows a single SEC peak in chloroform but three peaks in acetone, which are ascribable to intermolecularly and intramolecularly associated complexes and nonassociated molecules. A three-arm star polymer with one isotactic chain and two syndiotactic chains shows a peculiar SEC behavior in acetone due to a braid type of intramolecular stereocomplex formation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 416–431, 2004     

Thermal transitions and polymer/polymer miscibility

Poly(vinyl chloride) was blended with ethylene-vinyl acetate copolymer containing 70 wt% of vinyl acetate. The system shows a single glass transition temperature for all compositions, indicating their miscibility. TheT _g vs. composition curves display an inflection, which changes with the chemical environment of the initial solution. The best fit to the shape of the curve was well reproduced by the Kovacs-Braun equation. The T _g values reveal local heterogeneity, which means no total miscibility at a molecular level. Negative values of the Flory-Huggins interaction parameter were obtained from the calorimetric data.Support for this research by CNP_q, FINEP and CAPES is appreciated.     

Converting water absorbent polymer to alcohol absorbent polymer

In this paper, a commercial water absorbent polymer based on poly (sodium acrylate) (PAANa) was converted to an alcohol absorbent polymer. PAANa collapses in alcoholic swelling media such as ethanol and methanol. In the present paper, first, a full interpenetrating polymer network (IPN) gel was prepared through immersing PAANa hydrogel in a solution containing 2‐acrylamido2‐methyl propane sulfonic acid (AMPS), polyethylene glycol dimetahcrylate and ammonium persulfate. The second network was formed in hydrated PAANa through heating. It was synthesized in two conditions by chemical crosslinker and crosslinker‐free. The IPN was acid treated to investigate the effect of removing Na⁺ on alcohol absorbency. The synthesized IPN gels have the ability of absorbing up to 21 and 39 g/g ethanol and methanol, respectively. The samples which were synthesized using the chemical crosslinker in the second stage had more alcohol absorbency in comparison with the crosslinker‐free samples. Unexpectedly, acid treatment caused a decrease in alcohol absorbency. The IPN gels were characterized through thermogravimetric analyses (TGA) and dynamic mechanical thermal analysis (DMTA). The DMTA results confirmed the IPN structure of the gels, two distinctive peaks, which can be attributed to PAANa, and poly (AMPS) was observed in tan delta figures. TGA thermograms demonstrated that IPN had lower thermal stability in comparison with the initial PAANa, which can be attributed to higher vulnerability of SO₃H group for degradation that reduced initial decomposition temperature. Copyright © 2012 John Wiley & Sons, Ltd.     

Welding dynamics in an atomistic model of an amorphous polymer blend with polymer–polymer interface

We consider an atomistic model of thermal welding at the polymer-polymer interface of a polyetherimide/polycarbonate blend, motivated by applications to 3D manufacturing in space. We follow diffusion of semiflexible chains at the interface and analyze strengthening of the samples as a function of the welding time t_w by simulating the strain–stress and shear viscosity curves. The time scales for initial wetting, and for fast and slow diffusion, are revealed. It is shown that each component of the polymer blend has its own characteristic time of slow diffusion at the interface. Analysis of strain–stress demonstrates saturation of the Young's modulus at t_w = 240 ns, while the tensile strength continues to increase. The shear viscosity is found to have a very weak dependence on the welding time for t_w > 60 ns. It is shown that both strain–stress and shear viscosity curves agree with experimental data.     

The influence of polymer morphology on polymer film electrochemistry

The electrochemical behavior of functionalized polystyrene-coated electrodes shows a marked dependence on the nature of the electrolyte ions. Scanning electron microscope and surface profile measurements are presented which show that changes in polymer film volume and morphology accompany electrochemical oxidation. Changing polymer morphology by doping the films with soluble monomers during preparation is shown to produce large changes in electrochemical response. Diffusion coefficients were determined for a neutral organic dye dopant in each of the polymer films investigated, and these correlate very well with the oxidation overpotentials observed electrochemically. The nature of polymer film/solvent interactions and the mechanism by which counter ions penetrate the polymer phase is discussed and is related to other physical properties of amorphous polymers in terms of free volume concepts.     

Liquid-liquid phase equilibria in polymer solutions and polymer mixtures

The pressure dependence of liquid-liquid equilibria in weakly interacting binary macromolecular systems (homopolymer solutions and blends) will be discussed. The common origin of the separate high-temperature/low-temperature and high-pressure/low-pressure branches of demixing curves will be demonstrated by extending the study into the region of metastable liquid states including the undercooled, overheated and stretched states (i.e. states at negative pressures). The seemingly different response of the UCST-branch of solutions and blends when pressurized (pressure induced mixing for most polymer solutions, pressure induced demixing for most blends) will be explained in terms of the location of a hypercritical point found either at positive (most solutions) or negative pressure (most blends). Further, it is shown that the pressure dependence of demixing of homopolymer solutions and blends may be described using a ‘master-curve’ which, however, is sometimes partly masked by degradation or by vapour-liquid and/or solid-liquid phase transitions. Experimental results demonstrating the extension of liquid-liquid phase boundary curves into the metastable regions will be presented, and the existence of solubility islands in the vicinity of the hypercritical points discussed.     

Reduction of polymer surface tension by crystallized polymer nanoparticles

Self-consistent field theory is applied to investigate the effects of crystallized polymer nanoparticles on polymer surface tension. It is predicted that the nanoparticles locate preferentially at the polymer surface and significantly reduce the surface tension, in agreement with experiment. In addition to the reduction of surface tension, the width of the polymer surface is found to narrow. The reduced width and surface tension are due to the smaller spatial extent of the nanoparticles compared to the polymer. This allows the interface to become less diffuse and so reduces the energies of interaction at the surface, which lowers the surface tension. The solubility of the surrounding solvent phase into the polymer melt is mostly unchanged, a very slight decrease being detectable. The solubility is constant because away from the interface, the system is homogeneous and the replacement of polymer with nanoparticles has little effect.     

Compatibilizer-aided toughening in polymer blends consisting of brittle polymer particles dispersed in a ductile polymer matrix

Blending brittle polymer particles in a ductile polymer matrix is a new way to obtain toughened plastics. Although the nylon-6/poly(acrylonitrile-co-styrene) (SAN) system is a ductile/brittle combination, the blend does not result in a toughened plastic. We have investigated the effect of adding a small amount of a third component, poly(styrene-co-maleic anhydride) (SMA), to the nylon/SAN system. SMA significantly improves the tensile and impact strength of the blend. Morphological observations indicate a finer dispersion of the SAN particles when SMA is present in the blend. The improved dispersion is attributed to the formation of nylon-SMA graft copolymer, and infrared analysis supports this supposition. That is, a “compatibilizer” seems to be produced during melt mixing of the ternary system. The role that the compatibilizer plays in improving the stress transfer in the two-phase system and its potential to induce a brittle-ductile transition of the glassy SAN particles are considered to explain the toughening mechanism.     

Lens epithelial cell response to polymer stiffness and polymer chemistry

Posterior capsule opacification (PCO) is the most common complication of cataract surgery, and intraocular lens (IOL) implantation is the standard of care for cataract patients. Induction of postoperative epithelial-mesenchymal transition (EMT) in residual lens epithelial cells (LEC) is the main mechanism by which PCO forms. Previous studies have shown that IOLs made with different materials have varying incidence of PCO. The aim of this paper was to study the interactions between human (h)LEC and polymer substrates. Polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA) and 3-methacryloxypropyl tris(trimethylsiloxy)silane (TRIS) were synthesized and evaluated due to the clinical use of these materials as ocular biomaterials and implants. The chemical properties of the polymer surfaces were evaluated by contact angle, and polymer stiffness and roughness were measured using atomic force microscopy. In vitro studies showed the effect of polymer mechanical properties on the behavior of hLECs. Stiffer polymers increased α-smooth muscle actin expression and induced cell elongation. Hydrophobic and rough polymer surfaces increased cell attachment. These results demonstrate that attachment of hLECs on different surfaces is affected by surface properties in vitro, and evaluating these properties may be useful for investigating prevention of PCO.     

Sandwich structure containing liquid crystal polymer grafted on polymer support

Graft post-polymerization of mesogenic monomers onto fluorine-containing polymer support was initiated by the simultaneous action of vacuum ultraviolet radiation and atomic oxygen. The resultant two-layer structure possesses the combined physical–mechanical properties of the polymer-supporting film and the optical characteristics of the anisotropic liquid crystal layer.     

Topological polymer chemistry by dynamic selection from electrostatic polymer self-assembly

A collection of recent developments in topological polymer chemistry is presented. First, topological isomerism occurring on randomly coiled, flexible polymer molecules having cyclic and linear structures is discussed. Second, an electrostatic self-assembly and covalent fixation strategy has been developed for the synthesis of polymeric topological isomers. These isomers have double cyclic, manacle-, and theta-shaped constructions, and are prepared by using either linear or star telechelic polymer precursors having moderately strained cyclic ammonium salt groups, which carry multifunctional carboxylate counteranions. A technique of reversed-phase chromatography (RPC) is demonstrated as an effective means to separate polymers with different topologies, especially polymeric topological isomers. A further extension of topological polymer chemistry has been observed by dynamic selection from electrostatic polymer self-assembly to enable the effective formation of tadpole-shaped, cyclic-linear hybrid topologies.     

聚合物纳米材料研究进展——Ⅰ.纳米聚合物

聚合物纳米材料包括纳米聚合物和聚合物／无机纳米复合材料。本文综述了纳米聚合物的研究进展，重点介绍了分子自组装，微乳液聚合，模板聚合，树枝状聚合物，超支化聚合物，机械粉碎，相反转技术的研究进展。     

硅氧烷基聚合物电解质*

聚合物锂离子电池的核心技术是研制高离子传导率、适宜机械性能以及化学和电化学性能稳定的聚合物电解质材料。在众多寻求高性能聚合物电解质的研究工作中,由于硅氧烷基聚合物电解质具有灵活多样的分子结构设计、易于合成实施、优异的电化学性能和室温电导率等特点,一直是人们关注的热点领域。本文综述了近年来新型硅氧烷基聚合物电解质的设计与合成的研究工作,重点介绍了采用聚硅氧烷嵌段、接枝聚合物通过共混、互穿网络结构、交联网络结构以及无机-有机复合等方法开展的相关聚合物电解质的研究工作。同时也介绍了聚硅氧烷电解质的研究方法和基于聚硅氧烷电解质的应用研究进展。     

聚合物纳米材料研究进展——Ⅱ.聚合物/无机纳米复合材料

复合物纳米材料包括纳米聚合物和聚合物／无机纳米复合材料。本文综述了聚合物／无机纳米复合材料的研究进展，重点介绍了溶胶－凝胶法，原位生成法，模板法，插层复合，沉积法，机械粉碎，分子平壤 ，溶液或融混合法的研究进展。     

Nanocomposite polymer hydrogels

The technological need for new and better soft materials as well as the drive for new knowledge and fundamental understanding has led to significant advances in the field of nanocomposite gels. A variety of complex gel structures with unique chemical, physical, and biological properties have been engineered or discovered at the nanoscale. The possibility to form self-assembled and supramolecular morphologies makes organic polymers and inorganic nanoparticles desirable building blocks for the design of water based gels. In this review, we highlight the most recent (2004–2008) accomplishments and trends in the field of nanocomposite polymer hydrogels with a focus on creative approaches to generating structures, properties, and function within mostly biotechnological applications. We examine the impact of published work and conclude with an outline on future directions and challenges that come with the design and engineering of new nanocomposite gels.     

Macroscopic polymer analogues

Disordered fiber mats made of glass microfibers (GMF) were studied using small-angle light scattering (SALS), ultrasmall-angle X-ray scattering (USAXS), SEM, and optical microscopy. The morphological scaling of these materials in the micron scale was very similar to that of polymers in the nanometer scale. In some fiber mats, such as GMF, the structure is randomized at the time of formation, leading to a statistical analogy with the thermal randomization that occurs in nanometer-scale, high polymers. Analogues for the coil radius-of-gyration, persistence unit, and scaling regimes exist in such fiber mats and may be a useful feature both for modeling thermally equilibrated polymeric systems, as well as furthering the understanding of the physical properties of fiber mats through analogy with the theoretical understanding of thermally equilibrated polymeric systems. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3147–3154, 1998     

Cylindrical polymer brushes

In recent years, research on cylindrical polymer brushes (or molecular bottlebrushes) has received significant attention. In this article, we discuss various strategies for their synthesis and the unique properties arising from their regular multibranched structure. Some recent advances in the application of cylindrical polymer brushes are highlighted. Amphiphilic core– shell cylindrical polymer brushes, for example, have been successfully used as single molecular templates for inorganic nanoparticle formation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3461–3481, 2005     

Polyferrocenylsilane-based polymer systems

The study of metallopolymers has blossomed into a mature field over the last few decades. Especially, polyferrocenylsilane (PFS) chemistry has taken a tremendous leap and continues to raise intense interest. Since the discovery of thermal ring-opening polymerization (ROP) of sila[1]ferrocenophanes, PFSs have been also accessed by anionic, cationic, transition-metal-catalyzed, and photolytic anionic ROP methodologies. A plethora of synthetic strategies have been devised, enabling access to a wide variety of copolymers, polyelectrolytes, and nanostructured materials. The distinctive physical properties and functions of many PFS-based polymers have been explored, leading to their apt exploitation in technical applications. Therefore, it is conceivable that PFS-related platforms might be indispensable nano-objects in the near future, as they stand on the verge of a new generation of sophisticated materials.