Novel degradable polymer networks containing acetal components

A novel copolymer network with acetal structure was prepared using bis[4-(vinyloxy)butyl](4-methyl-1,3-phenylene)biscarbamate(BECT)as the crosslinking agent.Firstly,a tri-copolymer of maleic anhydride(MAn),n-butyl vinyl ether(BVE)and 4-hydroxybutyl vinyl ether(HBVE)was synthesized via free-radical polymerization with 2,2′-azobisisobutyronitrile as the initiator.The tri-copolymer consisted of two sorts of alternating units,MAn-alt-BVE and MAn-alt-HBVE.The linear copolymer Poly((MAn-alt-BVE)-co-(MAn-alt-HBVE)...     

Synthesis of polymer networks containing degradable polyacetal segments

Four different routes for the production of polyacetal containing networks are described : (1) free radical copolymerization of α,ω-(meth)acrylate terminated polyacetals, (2) hydrosilylation reactions of α,ω-allyl terminated poly- (1,3-dioxolane) with a multifunctional silane, (3) modification of α,ω-hydroxy terminated poly(1,3-dioxepane) through reaction with 3-isocyanatopropyl-triethoxysilane and subsequent cross-linking under influence of H₂O and (4) cross-linking of multifunctional hydroxy-terminated polyacetals by reaction with a diisocyanate.     

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   

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.     

Extension and compression behavior of rubbery polymer networks

The elastic behavior of different types of rubbery polymers (natural rubber, polybutadiene, silicone, and polyisoprene) networks at various degrees of vulcanization and swelling was examined in extension and compression. The data are represented by the Mooney-Rivlin equation. In compression, although C₂ is zero, C₁ decreases strongly with increasing swelling to a limiting value which, in some cases, may be correlated with the value of C₁ found in extension and hence related to the theoretical modulus for highly swollen networks. A possible explanation is presented in terms of supramolecular order in the amorphous materials.     

Local composition in solvent + polymer or biopolymer systems

The focus of this paper is on the application of the Kirkwood-Buff (KB) fluctuation theory to the analysis of the local composition in systems composed of a low molecular weight solvent and a high molecular weight polymer or protein. A key quantity in the calculation of the local composition is the excess (or deficit) of any species i around a central molecule j in a binary mixture. A new expression derived by the authors (J. Phys. Chem. B 2006, 110, 12707) for the excess (deficit) is used in the present paper. First, the literature regarding the local composition in such systems is reviewed. It is shown that the frequently used Zimm cluster integral provides incorrect results because it is based on an incorrect expression for the excess (or deficit). In the present paper, our new expression is applied to solvent + macromolecule systems to predict the local composition around both a solvent and a macromolecule central molecule. Five systems (toluene + polystyrene, water + collagen, water + serum albumin, water + hydroxypropyl cellulose, and water + Pluronic P105) were selected for this purpose. The results revealed that for water + collagen and water + serum albumin mixtures, the solvent was in deficit around a central solvent molecule and that for the other three mixtures, the opposite was true. In contrast, the solvent was always in excess around the macromolecule for all mixtures investigated. In the dilute range of the solvent, the excesses are due mainly to the different solvent and macromolecule sizes. However, in the dilute range of the macromolecule, the intermolecular interactions between solvent and macromolecule are mainly responsible for the excess. The obtained results shed some light on protein hydration.     

Peptide dissociation in solution or bound to a polymer: comparative solvent effect

Dissociation of peptide when in solution or attached to a polymer was investigated. Magnified solvation of peptide-resins occurred in solvent with similar polarity. Conversely the solubilization of peptides was not usually directly related to the medium polarity. The greater the difference between acidity and basicity of solvent and its potential to form van der Waals interaction, the stronger its solubilization strength. Solvents with similar electrophilicity and nucleophilicity usually did not solvate aggregated peptide-resins nor dissolve peptides. The peptide solubilization in water-containing mixed solvents depended on combination of acidity/basicity of both components. Some criteria for choosing suitable solvents for peptide-resin solvation or peptide solubilization could be advanced.     

Phase behavior and photocrosslinking kinetics of semi-interpenetrating polymer networks prepared from miscible polymer blends

Mixtures of polystyrene derivatives (PSCS) and poly(vinyl methyl ether) (PVME) were made photocrosslinkable by chemically labeling PSCS chains with photoreactive anthracene. Miscibility of these anthracene-labeled PSCS/PVME blends was examined by light scattering under several crosslinking conditions in the one-phase region via photodimerization of anthracenes. As the reaction proceeds, the coexistence curve of PSCS/PVME blends shifts toward the low temperature side. By following the changes in concentration of anthracenes with irradiation time, it was found that the crosslinking reaction of PSCS chains in the blends does not follow the mean-field kinetics. However, it can be well expressed by the Kohlrausch–Williams–Watts (KWW) relaxation mechanism, indicating that the crosslinking reaction proceeds inhomogeneously in the blends. By scaling the reaction time with the average reaction rate obtained from the KWW equation modified for the reaction kinetics, all the crosslinking data obtained in the miscible region of the reacted blends fall on a single master curve. These experimental results suggest the universal behavior of the photocrosslinking kinetics obtained under the “shallow quench” conditions in the region far away from the coexistence curve of the reacting blends. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 455–462, 1998     

The size of a polymer in a symmetric solvent

Using a simple thermodynamic model, we derive an expression for the excluded volume parameter v of a polymer chain in a symmetric solvent (solvated by its own monomers). For a chain with a given segment length and number of monomers, this parameter determines whether the chain is collapsed or expanded. For the latter it determines the degree of expansion. Using a simple off-lattice version of Flory's model [P. J. Flory, Principles of Polymer Chemistry (Cornell University Press, Ithaca, 1953)] and relaxing the assumption of incompressibility, we obtain the result v=(1-kappa)rho(0), where kappa is the dimensionless compressibility and rho(0) the number density of solvent. In the incompressible limit (in the sense that kappa-->0) the chain is expanded and the inverse of the solvent number density determines the degree of expansion of the chain. Using the van der Waals equation of state to estimate kappa (allowing for nonzero compressibility in a system that can undergo a gas-liquid phase transition), the model predicts that upon raising the temperature at constant pressure there is both a lower (coil to globule) and upper (globule to coil) Flory temperature. This is in quantitative agreement with experiment and computer simulations.     

Equilibrium conformational dynamics of a polymer in a solvent

Molecular dynamics simulations were used to study the conformational dynamics of a bead-spring model polymer in an explicit solvent under good solvent conditions. The dynamics of the polymer chain were investigated using an analysis of the time autocorrelation functions of the Rouse coordinates of the polymer chain. We have investigated the variation of the correlation functions with polymer chain length N, solvent density rho, and system size. The measured initial decay rates gamma(p) of the correlation functions were compared with the predictions from a theory of polymer dynamics which uses the Oseen tensor to describe hydrodynamic interactions between monomers. Over the range of chain lengths considered (N = 30-60 monomers), the predicted scaling of gamma(p) proportional to N(-3nu) was observed at high rho, where nu is the polymer scaling exponent. The predicted gamma(p) are generally higher than the measured values. This discrepancy increases with decreasing rho, as a result in the breakdown in the conditions required for the Oseen approximation. The agreement between theory and simulation at high rho improves considerably if the theoretical expression for gamma(p) is modified to avoid sum-to-integral approximations, and if the values of (R(p)2), which are used in the theory, are taken directly from the simulation rather than being calculated using approximate scaling relations. The observed finite-size scaling of gamma(p) is not quantitatively consistent with the theoretical predictions.     

Stress relaxation in polymer networks: equilibrium behavior and dynamics

The elastic and relaxational properties of a polymer network have been calculated using a stress based formulation based on the Rouse mode expansion [W. L. Vandoolaeghe and E. M. Terentjev, J. Chem. Phys. 123, 34902 (2005)]. In this article, we propose an improved Rouse mode expansion incorporating appropriate boundary conditions. In contrast to the previous work, this improved formulation provides a smooth crossover from the classical equilibrium result of rubber elasticity to the shorter-time-scale Rouse relaxation of a polymer melt. Our results are compared with the classical phantom network approach in equilibrium, as well as both equilibrium and dynamic elongation experiments. The model captures the qualitative features of the data well and some of the quantitative aspects, such as the exponents seen in the dynamic modulus G(omega).     

Partition coefficient for small amounts of monomer,solvent, or plasticizer in a two-phased polymer blend or IPN

Theoretical calculations based on statistical thermodynamics are presented addressing the partitioning behavior of a monomer, solvent, or plasticizer in a two-phased polymer system. A phase-separated interpenetrating polymer network (IPN) consisting of a polyurethane (PU) and poly(methyl methacrylate) (PMMA) (50/50 by weight) is chosen as the model. Methyl methacrylate (MMA) is chosen as the partitioning small molecule, which is added at 20% by weight of the polymers. It is shown that the free energy of mixing this MMA is minimum only when the MMA is partitioned nearly uniformly between the two phases. It is also shown that such mixing of a small molecule in a polymer system is controlled by the entropic rather than enthalpic contributions to the free energy changes. © 1996 John Wiley & Sons, Inc.     

Polymer networks containing polyether,polyamine or polysulfide chains

An overview of newer or less-known synthetic methods for the synthesis of polymer networks containing ether, amine or sulfide functions or a combination of these functional groups with other functional groups, is presented. Emphasis is given on new methods starting from well - defined telechelic prepolymers. A number of these prepolymers are obtained by living cationic systems, more particularly cationic ring-opening and cationic vinyl ether polymerizations.     

Phase behavior and a modified Kwei equation for ternary polymer blends containing stereoregular PMMA

Previously, poly(methyl methacrylate) (PMMA) was found to be almost immiscible with poly(vinyl acetate) (PVAc) regardless of tacticity of PMMA and casting solvent. Poly(vinyl phenol) (PVPh) was found successful previously in making immiscible atactic PMMA/PVAc miscible. In this investigation, tacticity effect of PMMA on a ternary composed of PMMA, PVAc and PVPh was studied. Isotactic PMMA ternary was shown to be miscible in all the studied compositions on the basis of single T_g observation. However, syndiotactic PMMA ternary demonstrated immiscibility at ca. 25% PVPh and miscibility was observed at higher PVPh concentrations. A modified Kwei equation based on the binary interaction parameters was proposed to describe the experimental T_g of the miscible ternary almost quantitatively.     

The vapour pressure of solvent above swollen polymer networks in relation to rubber elasticity theory

The difference between the vapour pressure of solvent above swollen crosslinked polyurethanes and that above linear polyurethane solutions has been determined experimentally. Comparison of the data over a range of volume fractions of solvent has enabled an estimate to be made of the factor B/A, the ratio of the “front factors” in the equation for the free energy of deformation of a crosslinked network. Previous experimental evidence, based on the modulus of crosslinked elastomers, has suggested that A is $\text{1}\text{2}$. The results of this work suggest that $\text{A = B}\text{=}\text{1}\text{2}$.     

Properties of wood-polymer composites with a polymer matrix containing sevilens

The effect of vinylacetate unit content in sevilen used as a polymer matrix or polyethylene compatibilizer on the properties of wood-polymer composites with a thermoplastic binders and filler of plant origin is studied. It is shown that the introduction of vinylacetate units decreases the tensile strength, contact elastic modulus, Brinell hardness, and water absorption of the composites, but increases the relative tensile elongation and impact viscosity without notch.     

Phase separation of polymer solutions on a solvent surface

Study of the dynamics of liquid droplets of dilute and semidilute polymer solutions on the surfaces of liquid subphases representing solvents for corresponding polymers has shown that a spot of a rather stable layer is formed on an air–liquid interface. The spot spreads over a liquid subphase surface to yield a monomolecular polymer layer. At the same time, the solvent passes into the solution, so that the polymer or its concentrated solution remains on the subphase surface. The polymer does not dissolve in the bulk subphase for several hours. The stability of the polymer spot has been explained under the assumption that the interfacial surface possesses elastic properties and hinders the penetration of macromolecules into the bulk subphase. Desolvation of macromolecules followed by phase separation occurs on the surface. The initial rate of the phase separation of the solution is rather high, while the time dependence of the diameter of the spreading spot is described by a scaling law with an exponent almost equal to 2/3.     

Effective spring description of a bubble or a droplet interacting with a particle

It is shown that the interaction of a particle with a liquid drop or a gas bubble may be quantitatively described over the whole distance regime by treating the fluid interface as a Hookean spring. An algorithm suitable for analyzing atomic force microscopy data suitable for a calculator or a spread-sheet is given and applied to data for oil drops.     

Coagulation of a polymer solution: Effect of initial dispersion of polymer in solvent

Modeling results indicate that a moderate increase in coarseness of the initial dispersion of the polymer in solution leads to a faster coagulation rate and to the formation of a more uniform structure. Such an increase in coarseness can be obtained either by bringing the polymer solution close to the solubility limit or by increasing the stiffness of the polymer chains. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2493–2497, 1998