Compressible or incompressible blend of interacting monodisperse star and linear polymers near a surface

We consider a lattice model of a mixture of repulsive, attractive, or neutral monodisperse star (species A) and linear (species B) polymers with a third monomeric species C, which may represent free volume. The mixture is next to a hard, infinite plate whose interactions with A and C can be attractive, repulsive, or neutral. These two interactions are the only parameters necessary to specify the effect of the surface on all three components. We numerically study monomer density profiles using the method of Gujrati and Chhajer that has already been previously applied to study polydisperse and monodisperse linear-linear blends next to surfaces. The resulting density profiles always show an enrichment of linear polymers in the immediate vicinity of the surface due to entropic repulsion of the star core. However, the integrated surface excess of star monomers is sometimes positive, indicating an overall enrichment of stars. This excess increases with the number of star arms only up to a certain critical number and decreases thereafter. The critical arm number increases with compressibility (bulk concentration of C). The method of Gujrati and Chhajer is computationally ultrafast and can be carried out on a personal computer (PC), even in the incompressible case, when simulations are unfeasible. Calculations of density profiles usually take less than 20 min on PCs.     

Synthesis of monodisperse polymers from proteins

Proteins are functional biopolymers; viewed as molecules, they are also monodisperse polyamides with chemically reactive side chains. This paper describes the use of proteins as starting materials for the synthesis of monodisperse polymers with nonbiological functionalities attached to the side chains. It demonstrates the complete derivatization of amine groups (lysine side chains and N-termini) on three different proteins by addition of activated carboxylate reagents in aqueous solutions containing sodium dedecyl sulfate (SDS), under denaturing conditions. Several different acylating reagents were used to generate derivatized proteins; the resulting compounds constitute a new class of monodisperse, semisynthetic polymers, having the potential for wide variation in the structure of the backbone and of the side chains. Modification of lysozyme on a gram scale demonstrated that the method can generate useful quantities of material.     

Preparation of monodisperse magnetic surface molecularly imprinted polymers for selective recognition of lincomycin hydrochloride in milk

Monodisperse magnetic surface molecularly imprinted polymers (M-MIPs) with a specificity for lincomycin hydrochloride (LIN) were successfully prepared using surface-initiated atom transfer radical polymerization on the monodisperse magnetic polymer (vinylbenzylchloride/divinylbenzene) (Fe₃O₄/P_VBC/DVB) with LIN as a template molecule and 4-vinyl pyridine as the functional monomer. The Fe₃O₄ magnetic nanoparticles embedded itself in the micropores of polymer (P_VBC/DVB) by reversibly swelling adsorption method in which the pores of the polymer are swollen by the solvent, and then the Fe₃O₄ magnetic nanoparticles enter the pores, and as the solvent evaporates the pores of the polymer back to their original size, and Fe₃O₄ magnetic nanoparticles are left in the pores. The composition and magnetic properties of the polymer were characterized using scanning elemental microscopy analysis, X-ray diffraction, Surface element analysis and vibrating sample magnetometer analysis. The results of this study showed that the M-MIPs had good specific recognition ability for LIN. The imprinting factor is 3.72. The specific recognition capability of the polymers was affirmed by high performance liquid chromatography analysis. The spiked recovery was 94.3%–98.2% with RSD ≤ 3.7%, and the minimum detection limit is 15.0?ng/g (S/N?=?3) indicating that this material has application value in the pretreatment of complex samples.     

Synthesis of linear monodisperse vinylene-linked phenothiazine oligomers

A series of linear monodisperse vinylene-linked phenothiazine oligomers have been synthesized by alternate Heck reaction and Wittig reaction in good yields. It was found that their absorption and fluorescence emission bands red-shifted with increasing phenothiazine units due to extending of the conjugated degree. The fluorescent quantum yield increased from OPTZ1 to OPTZ6, and the Φ_F of OPTZ6 was close to phenothiazine-based polymers.     

Chemorheology of linear polymers

The structural changes brought about by chemical reactions are reflected in the viscoelastic behavior of polymers. Viscoelastic behavior induced by such chemical reactions is called chemorheology. This phenomenon is not readily observed in linear polymers, because molecular flow by diffusion is generally much more rapid than relaxation or flow caused by chemical reaction. It has become possible, however, to treat chemorheology of linear polymers theoretically by taking such physical flow into consideration. The experimental results for linear polystyrene compared with the theoretical ones are described in this paper. Good agreement between theoretical results and experimental ones is obtained for monodisperse polystyrene with low concentration of accelerators.     

Solid-state phase behavior and molecular-level mixing phenomena in a strongly interacting polymer blend

This research contribution addresses mixing phenomena in a polymer blend that exhibits strong intermolecular association and bieutectic phase behavior. Molecular-level observations of specific interactions between dissimilar blend components have been obtained from high-resolution solid-state proton and carbon-13 nuclear magnetic resonance (NMR) experiments at ambient temperature. Results illustrate mixing effects on the isotropic chemical shifts of the critical component in a completely or partially phase-mixed blend. Perturbations in the NMR spectra result from conformational changes, hydrogen bonding, molecular complexation, or altered packing geometries that occur concomitantly with the mixing process. More convincing evidence that two components of a strongly interacting blend reside in a near-neighbor environment is obtained from the measurement of proton spin diffusion between dissimilar species. Proton spin diffusion is measured directly via the high-resolution CRAMPS experiment (Combined Rotation and Multiple Pulse Spectroscopy) in a molecular complex of poly (ethylene oxide) and resorcinol. A primary objective of this research endeavor is to bridge the gap between macroscopic and molecular-level probes of phase behavior and intermolecular association in mixtures that form molecular complexes. In this respect, the temperature -composition projection of the thermodynamic phase diagram is generated for binary mixtures of poly (ethylene oxide) and resorcinol, whose interaction sites are characterized via solid-state NMR. Under fortuitous conditions that are related to the overall mixture composition, two morphologically and crystallographically inequivalent phenolic ¹³C NMR signals are identified for resorcinol when the blends exist in a two-phase region below the eutectic solidification temperature. The success of this proposed structure–property relationship scheme, which bridges molecular-level mixing phenomena (via NMR) with solid-state phase behavior (via differential scanning calorimetry) depends on our ability to understand material properties at a level where continuum hypotheses are no longer valid.     

Anisotropic colloidal particles interacting with polymers in a good solvent

We study the consequences of chain self-avoidance for the interaction between nonadsorbing polymers and colloidal particles of anisotropic shape, such as ellipsoids, lenses, and dumbbells. In the framework of a field theoretic operator expansion for small mesoscopic particles, we obtain exact results for self-avoiding polymers in d=2 spatial dimensions and we compare ideal and self-avoiding polymers in 2相似文献   

Facile synthesis of novel monodisperse linear 3,9-linked oligocarbazoles

Novel monodisperse linear 3,9-linked oligocarbazoles (OCAs) were prepared stepwise using Ullmann coupling reaction in seal-tubes. The resulting OCAs were soluble in common organic solvents. The UV-vis spectra of OCAs exhibited small red shift and their intensities increased linearly with the increase of the carbazole moieties, suggesting that no intramolecular π-interactions appeared at ?8-mer. All the OCAs gave strong fluorescence and it was found that the conjugated degree of linear OCAs would be saturated when the number of carbazole units reaches four.     

Phase relationships in a ternary solution composed of a solvent and two monodisperse homologous polymers

Exact expressions are derived for the spinodal, critical conditions, and separation factor of a ternary solution consisting of a pure solvent and two monodisperse homologous polymers in which the Flory-Huggins interaction parameter χ depends separately on the concentrations of the polymer components. The results allow one to see the difference from previous expressions obtained with χ depending on the total concentration of the polymer, and are expected to be useful for experimental determination of the Gibbs free energy of ternary solutions.     

Segmental distribution properties of a polymer chain near an interacting barrier

The exact distribution of segments for self-avoiding walks of lengths N=4–14 bonds in the presence of an interacting barrier on the diamond lattice has been obtained by the method of direct enumeration. Behavior for the infinite chain was estimated and compared with Rubin's results for the normal random walk. It is shown that the onset of a well defined transition for the self-avoiding walk coincides with the location predicted for the normal random walk. It was found that for a self-avoiding walk a plot of θ₂ (the fraction of segments in level z) versus the interaction parameter φ is shifted to the right (higher φ), for all z, as compared with a similar plot for the normal random walk. Conditional probabilities for a self-avoiding walk having its t th segment in level z (when φ=0) are reported.     

Colloidal dynamics near a particle-covered surface

How the diffusive dynamics of colloidal spheres changes in the vicinity of a particle-coated surface is of importance for industrial challenges such as fouling and sedimentation as well as for fundamental studies into confinement effects. We addressed this question by studying colloidal dynamics in a partially coated surface layer, using video microscopy. Particle mean squared displacement (MSD) functions were measured as a function of a (local) effective volume fraction (EVF), which was varied by making use of gravity settling. Comparison of MSDs at the bare and coated surfaces for EVF of 0.2-0.4 revealed that at the latter surface the motion amplitudes are strongly reduced, accompanied by a sharp transition from diffusive to nearly caged motion. This clearly indicates that the surface-attached particles cannot be taken into account via volume fraction and that their immobility has a distinct effect. For EVF > 0.45, the caging becomes dominated by the suspended particles, making the dynamics at the bare and coated surfaces similar.     

Dendronized protein polymers: synthesis and self-assembly of monodisperse cylindrical macromolecules

Monodisperse dendronized protein polymers (DPPs), cylindrical dendrimers containing protein core, can be efficiently produced through a combined modular biosynthetic strategy. These DPP materials possess predictable size, shape, and solubility. In organic solutions, the DPPs self-assemble to form highly ordered liquid crystalline structures with nanoscale order controlled by their exact molecular dimensions.     

Highly practical and general synthesis of monodisperse linear pi-conjugated oligoenynes and oligoenediynes with either trans- or cis-olefin configuration

Efficient and practical synthesis of a variety of 1-iodo-4-(trimethylsilyl)but-1-en-3-yne derivatives 1 and 2 with trans- and cis-olefin configuration was described. Their repeated use as building blocks allowed the facile synthesis of trans- and cis-oligoenynes, respectively. Development of a highly practical method for preparing monodisperse trans- and cis-oligoenediynes having the effective conjugation length was also accomplished by using 5 and 4, which can be readily prepared from 1 and 2, respectively.     

Micro-emulsion synthesis of monodisperse surface stabilized silicon nanocrystals

Silicon nanocrystals with a uniform size distribution were synthesized in inverse micelles using powerful hydride reducing agents. The silicon nanocrystals surfaces were then stabilized with 1-heptene to produce particles with strong blue photoluminescence.     

Vinyl ethers with a functional group: Living cationic polymerization and synthesis of monodisperse polymers

The living cationic polymerization of vinyl ethers (VEs) having a (polar) functional pendant has been achieved by the hydrogen iodide/iodine (HI/I₂) initiating system to give polymers with a very narrow molecular weight distribution (MWD) (M_w/M_n ≤ 1.2). The functional pendants include benzyl, saturated or unsaturated ester, (poly) oxyethylene, and substituted phenoxyl groups. Although these polar groups often disturb cationic vinyl polymerization by inducing chain transfer and termination, the HI/I₂ initiator cleanly polymerized the “functionalized” VEs without side reactions, mostly in nonpolar media at low temperatures below −15 °C. The HI/I₂-initiated living polymerization also provided facile methods to synthesize new functional polymers, including water-soluble polymers, macromolecular amphiphiles, and macromers, all having a narrow MWD. The simplest example is the living polymerization of VEs carrying an oxyethylene chain [-(CH₂CH₂O)_n-R] as pendant, which directly yields water-soluble polymers. The debenzylation of poly(benzyl VE) prepared with HI/I₂ led to poly(vinyl alcohol). Polymers of the saturated ester-containing monomers (2-acetoxyethyl and 2-benzoyloxyethyl VEs) were readily hydrolyzed into poly (2-hydroxyethyl VE), soluble in water and swellable in methanol. This lead was extended to the synthesis of a new amphiphile, poly(cetyl VE-b-2-hydroxyethyl VE), from a block copolymer of cetyl and 2-acetoxyethyl VEs prepared by their sequential living polymerization initiated with HI/I₂. An adduct between HI and 2-vinyloxyethyl methacrylate [CH₃-CH(I)-OCH₂CH₂OCOC(CH₃) =CH₂] was found to initiate living polymerizations of VEs in the presence of iodine; the products were methacrylate-type macromers carrying a poly(VE) side chain with a narrow chain-length distribution.     

Monte Carlo simulation of the interchain exchange reaction in a blend of incompatible polymers

The interchain exchange reaction in a blend composed of two contacting layers of incompatible A and B homopolymers was simulated by means of the dynamic off-lattice Monte Carlo method. The evolution of local molecular-mass and block mass distributions, depending on the effective temperature and the reaction rate, was studied for the first time. It was shown that the components interpenetrate as the copolymer forms in the interphase layer and the average block length decreases below a certain, temperature-dependent value. The state of dynamic equilibrium, whose characteristics are determined mainly by temperature, is established in the system. The time of establishment of equilibrium and the intensity of compatibilization at the early steps of the process are controlled by the rate of the reaction. The results of the study allow the contribution of the reaction to the interchange processes to be evaluated.     

Anisotropic Brownian diffusion near a nanostructured surface

The Brownian diffusion of sub-micrometer-sized particles (diameter 0.52 microm) in the vicinity of a nanostructured surface was experimentally characterized. The surface consisted of a repeating pattern of rectangular grooves with depth 35 nm and pitch 400 nm. It was found that the one-dimensional particle diffusivity parallel to the nanogrooves was significantly higher than the diffusivity perpendicular to the grooves (1.518+/-0.274 (S.E.) microm2/s compared to 0.704+/-0.090 microm2/s). No such anisotropy in the one-dimensional Brownian diffusivity was found for particles near a flat surface.     

Adsorption of interacting oligomers and polymers at an interface

We discuss in a qualitative way the physical background of a recently developed polymer adsorption theory, in which all the possible chain conformations for interacting chain molecules near an adsorbing interface are taken into account. Any conformation is described as a step-weighted random walk in a lattice. Each step is weighted according to a segmental weighting factor that contains the adsorption energy (for segments in contact with the surface), the entropy of mixing, and the attraction or repulsion between segments and solvent molecules. A suitable computing method is used to calculate the contribution of all chain conformations to the concentration profile, to the adsorbed amount, to the fraction of trains, loops and tails, to the layer thickness, etc. The theory is valid for any chain length and any concentration in the solution.Results for various chain lengths are given. Oligomers have a low affinity for the surface, whereas polymer adsorption isotherms are of the well known high affinity type. Three concentration regimes can be distinguished. In (extremely) dilute solutions the molecules on the surface adsorb as isolated chains (the Henry region).     

High-pressure XeNMR study of supercritical xenon interacting with polymers

High-pressure ¹²⁹XeNMR experiments have been performed by using a newly designed probe. ¹²⁹XeNMR spectrum for the mixture of Xe and a polymer, either bisphenol-A polycarbonate or polytetrafluoroethylene, consists of two lines in a pressure range of 0.3–10 MPa. ¹²⁹XeNMR chemical shift (δ) for the free Xe is mainly governed by the Xe–Xe interactions. δ for Xe confined in the micropore of polymers is strongly affected by the Xe-wall interactions. It is found that δ of the confined Xe is mainly determined by a sort of ‘virtual pressure' and is not influenced by a drastic change of the free Xe density in the critical region.     

Chemorheology of linear polymers. II

The chemical stress relaxation of crosslinked polymers had long been studied. The chemorheology of linear polymers is difficult to study because molecular flow by diffusion is generally much more rapid than relaxation or flow caused by chemical reaction. Our previous paper dealt with the chemorheology of linear polymers on taking such physical flow into consideration. By using another modified expression suggested by Tobolsky, good consistency between the theoretical chemical stress relaxation curve and an experimental one was obtained for polydisperse polystyrene and the commercial polystyrene used.