Visualization of deformation-induced structural rearrangements in amorphous polymers

A technique is proposed for decorating amorphous polymers: Before the deformation (shrinkage) of an amorphous polymer, its surface is decorated with a thin metal coating. The subsequent deformation is accompanied by surface structure formation, which makes the processes that occur in the polymer visible. The proposed technique makes it possible to visualize and describe the mechanism of transfer of the polymer from the surface into the bulk and vice versa and to obtain direct information about the direction of the actual local stress. The technique makes it possible to obtain information about the topological heterogeneity of rubber networks, to reveal the features of structural rearrangements that occur during the cold rolling of amorphous polymers, and to describe the phenomenon of self-elongation during annealing of the oriented PET. These microscopic data explain the following features of the structural and mechanical behavior of glassy polymers from a unified viewpoint: stress relaxation in a polymer in the elastic (Hookean) region of the stress-strain curve, an increase in stress in a deformed glassy polymer during its isometric annealing below T _g, the low-temperature shrinkage of a deformed polymer glass in the strain range below its yield point, the storage of internal energy in a deformed glassy polymer in the strain range below the yield point, some anomalies of thermophysical properties, and some other features.     

Metal‐induced optical sensing and optical switching in poly(pyridyl phenylene)

The synthesis of a conjugated polymer containing pyridyl units in the polymer backbone was successfully carried out with 2,6‐dibromopyridine and a diboronic acid derivative via the Suzuki coupling reaction. This polymer had a number‐average molecular weight of 4000 and excellent solubility in conventional organic solvents; this suggested the effect of the incorporation of dialkoxy side chains. A metallochromic phenomenon with ferric ions was clearly observed in spin‐coated films and solutions of the polymer. The response of the absorption and the fluorescence changes of the polymer films were rapid and were reproduced more than 15 times. A lightly bound intermolecular interaction between the pyridine ligand and cation was presumed to be responsible for the facile optical switching property of the polymer films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2444–2450, 2004     

含氧光敏引发体系的研究——Ⅵ.二苯酮/三乙胺体系引发光聚合过程中的再次引发效应

过去,作者曾发表了多种光敏引发体系引发烯类单体光聚合的工作,在研究2,2-二甲氧基苯乙酮在氧存在下引发甲基丙烯酸甲酯光聚合时,结合在聚合物链端的引发剂碎片具有光化学活性,在光聚合反应中产生高分子自由基,发生再次聚合,出现高分子量     

含氧光敏引发体系的研究——Ⅵ.二苯酮/三乙胺体系引发光聚合过程中的再次引发效应

A sequential photoinitiation. phenomenon was found in the benzophenone/triethylamine/ MMA radical photopolymerization system, which leads to increase of molecular weight, amine content of polymer formed with progressive irradiation time. The results, obtained demonstrate that the sequential photoinitiation originates from the photoreaction of active amine groups at the polymer chains with excited benzophenones producing a polymer radicals, which induce sequential polymerization. The effects of benzophenone and amine concentrations,oxygen co-ntent and chain requlator were studied. Reaction mechanism was also discussed.     

On-chip sample pretreatment using a porous polymer monolithic column for solid-phase microextraction and chemiluminescence determination of catechins in green tea

A porous polymer monolithic column for solid-phase microextraction and chemiluminescence detection was integrated into a simple microfluidic chip for the extraction and determination of catechins in green tea. The porous polymer was prepared by poly(glycidyl methacrylate-co-ethylene dimethacrylate) and modified with ethylenediamine. Catechins can be concentrated in the porous polymer monolithic column and react with potassium permanganate to give chemiluminescence. The microfluidic chip is reusable with high sensitivity and very low reagent consumption. The on-line preconcentration and detection can be realized without an elution step. The enrichment factor was calculated to be about 20 for catechins. The relative chemiluminescence intensity increased linearly with concentration of catechin from 5.0 × 10(-9) to 1.0 × 10(-6) M and the limit of detection was 1.0 × 10(-9) M. The proposed method was applied to determine catechin in green tea. The recoveries are from 90% to 110% which benefits the actual application for green tea samples.     

On the Schroeder paradox for ion-exchange polymers

The known Schroeder paradox, i.e., a difference in the degree of swelling of ion-exchange polymers at equilibrium with liquid water and its vapor, has been discussed. It has been noted that there is no paradoxicality in this phenomenon. An example of different “swelling” based on trivial physical considerations has been presented. A simple mechanism has been proposed for increased swelling of an ion-exchange polymer immersed in liquid water, this mechanism being associated with the action of the Maxwell stresses at a polymer/electrolyte interface. The predicted values of the “excess” swelling have been shown to correspond to the data of real experiments.     

A model for the Gibbs energy of aqueous solutions of polyelectrolytes

A new model for the excess Gibbs energy of aqueous solutions of polyelectrolytes is presented and applied for the correlation of the activity of water in aqueous solutions of polyelectrolytes without as well as with an added (single) salt. The model considers the phenomenon of counterion condensation, i.e., the partial dissociation of highly charged polyelectrolytes in water. Three parameters (a binary interaction parameter between polymer segments, the equilibrium constant of the dissociation reaction and a parameter which accounts for the polymer configuration) were fitted to the experimental results. The model allows for a reliable correlation of experimental results for the osmotic coefficient of aqueous solutions of a single polyelectrolyte (without as well as with an added salt).     

Self-oscillation mechanism of necking on extension of polymers

A new phenomenon in necking of some polymers, including poly(ethylene terephthalate) (PETP) was detected. It was found that extension of PETP films under certain conditions results in periodic stress oscillations and a periodic change in appearance of the sample. The conditions at which self-oscillations appear have been determined, and the principal regularities of this regime of deformation are described. The following factors are critical for the appearance of self-oscillation: speed of straining and compliance of the sample. The self-oscillation of stress and formation of the periodic transverse bands is attributed to heat dissipation during necking corresponding to local temperature jumps and periodic strong variation of elasticity modulus due to poor heat conductivity of the polymer. Changing the external conditions of heat transfer influences the possibility and development of the effect. The phenomenon is common for various crystallizing polymers, being dependent on physical properties of the polymer and conditions of deformation.     

Diffusion in polymer–solvent systems. II. A predictive theory for the dependence of diffusion coefficients on temperature,concentration, and molecular weight

A new free-volume theory is combined with the thermodynamic theory of Flory and the entanglement theory of Bueche to provide a means of predicting the temperature, concentration, and molecular weight dependence of mutual-diffusion coefficients in amorphous polymer–solvent systems. The predictions of the theory are compared with actual data for the ethylbenzene–polystyrene system.     

Large-volume methacrylate monolith for plasmid purification. Process engineering approach to synthesis and application

The extent of exothermicity associated with the construction of large-volume methacrylate monolithic columns has somewhat obstructed the realisation of large-scale rapid biomolecule purification especially for plasmid-based products which have proven to herald future trends in biotechnology. A novel synthesis technique via a heat expulsion mechanism was employed to prepare a 40 mL methacrylate monolith with a homogeneous radial pore structure along its thickness. Radial temperature gradient was recorded to be only 1.8 degrees C. Maximum radial temperature recorded at the centre of the monolith was 62.3 degrees C, which was only 2.3 degrees C higher than the actual polymerisation temperature. Pore characterisation of the monolithic polymer showed unimodal pore size distributions at different radial positions with an identical modal pore size of 400 nm. Chromatographic characterisation of the polymer after functionalisation with amino groups displayed a persistent dynamic binding capacity of 15.5 mg of plasmid DNA/mL. The maximum pressure drop recorded was only 0.12 MPa at a flow rate of 10 mL/min. The polymer demonstrated rapid separation ability by fractionating Escherichia coli DH5alpha-pUC19 clarified lysate in only 3 min after loading. The plasmid sample collected after the fast purification process was tested to be a homogeneous supercoiled plasmid with DNA electrophoresis and restriction analysis.     

端基功能化聚合物的表面性能

综述了端基功能化聚合物表面结构与性能的最新研究进展.聚合物端基功能化是实现聚合物表面改性的一种有效技术.通过端基功能化可以精确控制聚合物表面功能基团的种类和数量,从而影响聚合物表面的化学结构与性能.重点论述了功能化端基在聚合物表面的离析现象和产生这一现象的原因,以及功能化端基对聚合物表面分子运动能力的影响.本文还介绍了近年来用于研究端基功能化聚合物表面的表征新技术,如SFG、NR、SSIMS等.对端基功能化聚合物表面的环境响应性也进行了阐述.指出了利用不同功能化端基可以有效地控制聚合物表面的亲疏水性.并对端基功能化聚合物的应用进行了展望.     

Synthesis of Organic-Inorganic Hybrid Materials by Incorporation of Molybdenum and Tungsten Hydrated Oxides in Polymers

In order to obtain new organic-inorganic hybrid materials the method exploiting the phenomenon of polymer crazing was investigated. Polypropylene and polyethyleneterephtalate films were subjected to crazing to achieve high porosity. Incorporation of hydrated oxides of Mo and W in porous polymer matrix was performed by hydrolysis of alkoxides in pores using counterflow diffusion technique. It was shown that peculiarities of the hydrolysis of the initial compounds affect significantly the distribution of substances inside porous polymer matrix and the possibility of accumulation of inorganic component inside the film. Mo matter in contrast to W is easily incorporated in the polymer matrix to form a well-defined layer. These samples demonstrated high photosensitivity.     

Study on the relationship between the mechanical properties and processing for self-reinforced polymers: A method for estimating the theoretical strength of UHMWPE fiber

In this paper, a method for estimating the theoretical strength of polymer fiber from experiments was developed. It is based on a kinetic equation for bond rupture of overstressed Taut tie molecules (TTM) and/or trapped entanglement chains (TEC) in the disordered domain and is established by using the coefficient of overstressed TTM and/or TEC in the disordered domain as a variable. After integration and simplification, a general correlation between the tensile strength with the primary molecular weight, the processing condition, the testing condition and durability was obtained. When the draw ratio of processing and the primary molecular weight are extrapolated to infinity, a general relation between the actual tensile strength and the theoretical strength, the fraction of TTM and/or TEC (X_e3) in the disordered domain and the thermal fluctuation was obtained. Based on the relation, a method for estimating the theoretical strength of the polymer chain from the measurement of the actual tensile strength and the fraction of TTM and/or TEC is proposed. The theoretical strength of a PE chain was estimated by the method to be 30–40 Gpa.     

Properties of polyvinylchloride in solution: an hydrodynamic and vibrational spectroscopy study

The polymer polyvinylchloride has been studied in binary solvent mixtures and as a function of temperature in solution. A discontinuity of the polymer chain dimensions has been observed, as measured by hydrodynamic methods. This phenomenon is further examined by infrared and Raman spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1351–1356, 1999     

Nuclear magnetic resonance as a powerful tool for evaluation of intermolecular interaction: Correlation with rheological measurements of recycled nanocomposite

The degradation of polystyrene nanocomposite was carried out by mechanical recycling after multiple processing of thermo-oxidative ageing. It was found that the degradation of the quaternary salt present in the clay promotes degradation of the polymer. The clay exfoliation was affected by the nanocomposite degradation process as well as the dipolar interactions of polymer chains, which influences the physical and mechanical properties of the final nanocomposite. NMR is a powerful tool for the characterization at the molecular level; it is sensitive to variations in local segmental and global movements. The correlation between NMR relaxation and rheological analyses in polymer nanocomposites was observed. This study aims to understand the complex effects of degradation in polymeric systems containing nanoparticles. Several ¹H NMR relaxation parameters were analyzed. From the base line of the domain curves, the dipolar interaction phenomenon in polystyrene chains was investigated. The polymer chain heterogeneity was determined quantitatively from the MSE-FID, using a combination of Abragamian, Gaussian and exponential functions to fit experimental data. At least three domains: rigid, intermediate and mobile phases were identified based on the molecular mobilities.     

Single‐molecule imaging of photodegradation reaction in a chiral helical π‐conjugated polymer chain

How does the chemical reaction of a single polymer chain progress? This question is not proven, as long as it is studied the data of the ensemble average from the large number of molecules. In this study, we succeeded for the first time in the direct measurement of when, where, and how the chemical reaction of a polymer chain proceeds on a nanometer scale. That is, single‐molecule imaging of the photodegradation reaction of a chiral helical π‐conjugated polymer following laser irradiation of 405 nm was conducted. Analysis of the chemical kinetics showed that the photodegradation of the single polymer chain proceeded stepwise as a quantum phenomenon. When the motility of the chain‐end increased, reactivity of the photodegradation increased. It was also discovered that the photodegradation of the polymer chain proceeded continuously in one direction, like the “domino effect.” Our method allowed dynamic imaging of single polymer chains at a solid/liquid interface, and hence can be applied to the study of many types of polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4103–4107, 2010     

Self-assembly of electrospun polymer nanofibers: a general phenomenon generating honeycomb-patterned nanofibrous structures

A general phenomenon that electrospun polymer nanofibers self-assemble into honeycomb-patterned nanofibrous structures (HNFSs) is reported. We used electrospinning to produce charged polymer nanofibers, which were kept in liquid state (wet) on landing on the substrates by appropriately controlling the electrospinning conditions. Driven by the competitive actions of surface tension and electrostatic repulsion, these charged wet nanofibers self-assemble into the HNFSs. Fabrication of the well-defined three-dimensional HNFSs was successfully demonstrated for three different polymers, that is, polyacrylonitrile, polyvinyl alcohol, and polyethylene oxide. The pore diameter of the obtained honeycomb structures spans a wide range from micrometers to over 200 μm with depths as large as over 150 μm. The pore walls are composed of uniaxially aligned polymer nanofibers.     

Near infrared (NIR) spectroscopy for in-line monitoring of polymer extrusion processes

In recent years, near infrared (NIR) spectroscopy has become an analytical tool frequently used in many chemical production processes. In particular, on-line measurements are of interest to increase process stability and to document constant product quality. Application to polymer processing e.g. polymer extrusion, could even increase product quality. Interesting parameters are composition of the processed polymer, moisture, or reaction status in reactive extrusion. For this issue a transmission sensor was developed for application of NIR spectroscopy to extrusion processes. This sensor includes fibre optic probes and a measuring cell to be adapted to various extruders for in-line measurements. In contrast to infrared sensors, it only uses optical quartz components. Extrusion processes at temperatures up to 300 degrees C and pressures up to 37 MPa have been investigated. Application of multivariate data analysis (e.g. partial least squares, PLS) demonstrated the performance of the system with respect to process monitoring: in the case of polymer blending, deviations between predicted and actual polymer composition were quite low (in the range of +/-0.25%). So the complete system is suitable for harsh industrial environments and could lead to improved polymer extrusion processes.