Monodisperse Polymer Research Articles

Pore size in one‐step swelling and polymerization of monodisperse polymer beads

Crosslinked polystyrene beads were prepared at low swelling ratios by one-step swelling and polymerization method. Pore size of the beads was observed based on the GPC calibration curves. It is found that: (1) the pore size increases as the swelling ratio decreases; (2) when a good solvent is used as the porogen the pore size increases with the crosslinking monomer content; and (3) at high crosslinking monomer content the pore size does not depend on the porogen solubility. The effects are discussed in terms of polymer miscibility, including phase separation between the seed and bead polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3270–3277, 2000

Kinetic Gelation Modeling of Controlled Radical Polymerizations

A kinetic gelation model has been developed that incorporates the kinetics of a living/controlled radical polymerization. Specifically, the kinetics of an iniferter polymerization were implemented in the model to determine the effect of the kinetics on the polymer structure. In particular, the replacement of the termination step with a reversible termination was examined. The model predicts the formation of more monodisperse linear polymers in the presence of an iniferter and a reversible termination reaction. When termination by combination is allowed to occur, the polydispersity increases. For cross-linking reactions, it was concluded that the iniferter only had an effect on reactions with small amounts of cross-linking agent, resulting in a delay in the gel point and a more heterogeneous structure. When the amount of cross-linking agent is increased, there is no difference in the network structure obtained by a cross-linking reaction with an iniferter versus a cross-linking reaction with the classical free-radical initiator.

The influence of polymer molecular-weight distributions on pulsed field gradient nuclear magnetic resonance self-diffusion experiments

The influence of polymer molecular-weight distributions on the outcome of pulsed field gradient (PFG) NMR self-diffusion experiments has been considered. The self-diffusion coefficient, D, of monodisperse poly(ethylene oxide) (PEO) polymers has been determined in order to accurately determine the scaling behavior of D both with molecular weight and concentration. In order to investigate the influence of polydispersity on the PFG NMR signal, a model system consisting of ten reasonably monodisperse PEO polymers was made, and the PFG NMR signal intensities were recorded at a low total concentration. The data were analyzed using both inverse Laplace transformation and nonlinear least-squares fitting to a prescribed distribution function of D. Finally, the molecular-weight distribution was obtained by use of the values of the scaling parameters. We also present some model calculations used to investigate the sensitivity of the degree of polydispersity on the NMR signal decays.

Determination of the relaxation time spectrum from dynamic moduli using an edge preserving regularization method

For the numerical determination of a continuous relaxation time spectrum from rheological data so-called regularization methods are necessary. The regularization method based on Tikhonov regularization and commonly used in rheology assumes the relaxation time spectrum to be smooth. Accordingly, this method is not able to properly resolve spectra containing edges or at least large curvatures as proposed in the literature. In order to reconstruct such spectra a novel edge preserving regularization (EPR) method was developed which extends the properties of the commonly used method. In order to demonstrate the efficiency of EPR it is compared with the commonly used regularization method by means of simulated and experimental data. This reveals that EPR is able to prove whether or not the theoretically predicted edge containing spectra for high-molecular-weight, monodisperse polymers are compatible with experimental data.

Filamentary dusty structures in RF inductive discharge

The results of the experimental investigation of the behaviour of micron-sized dust particles in plasma of an inductive RF discharge are presented. The discharge was initiated in different inert gases at a frequency of 100 MHz. The formation of ordered filamentary structures from monodisperse polymer particles is demonstrated and the conditions of their existence are discussed.

Mechanistic interpretation of base-catalyzed depolymerization of polystyrene

The effect of a base catalyst, MgO, on the decomposition of polystyrene was studied through degradation of both a monodisperse polymer (number average molecular weight = 50,500 g/mol) and a polystyrene mimic, 1,3,5-triphenylhexane (TPH), to determine the potential of applying base catalysts as an effective means of polymer recycling. The presence of the catalyst increased the decomposition rate of the model compound but decreased the degradation rate of polystyrene as measured by evolution of low molecular weight products. Although the model compound results suggest that the rate of initiation was enhanced in both cases by the addition of the catalyst, this effect is overshadowed for the polymer by a decrease in the ‘zip length’ during depropagation due to termination reactions facilitated by the catalyst. Due to the small size of the model compound, this effect does not impact its observed conversion since premature termination still affords a quantifiable low molecular weight product. A decrease in the selectivity to styrene monomer in the presence of MgO was observed for both polystyrene and TPH. Reconciliation of our results with those of Zhang et al. [Z. Zhang, T. Hirose, S. Nishio, Y. Morioka, N. Azuma, A. Ueno, H. Ohkita and M. Okada, Industrial and Engineering Chemistry Research, 34 (1995) 4514.] based on differences in the reactor configuration used is discussed.

Stress overshoot of polymer solutions at high rates of shear; Polystyrene with bimodal molecular weight distribution

Overshoot of shear stress, σ, and the first normal stress difference, N1, in shear flow was investigated for dilute solutions of polystyrene with very high molecular weight in concentrated solution of low M PS. In the case that the matrix was a nonentangled system, behavior of overshoot was similar to that of dilute solution of high M PS in pure solvent. The magnitudes of shear, γσm and γNm, corresponding to the peaks of σ and N1 lay on the universal functions of γ˙τR, respectively, proposed for dilute solutions in pure solvent. Here τR is the Rouse relaxation time for high M PS in the blend evaluated from dynamic modulus at high frequencies. In the case that the matrix was an entangled system, an additional σ peak was observed at high rates of shear at times corresponding to γσm = 2–3. This peak can be assigned to the motion of low M chains in entanglement network. When the matrix was entangled, stress overshoot was observed even at relatively low rates of shear, say γ˙τR < 10−2. This is probably due to the motion of high M chains in entanglement of all the chains. In this case the γσm and γNm values were higher than those expected for entangled chains of monodisperse polymer in pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2043–2050, 2000

Pore size in one-step swelling and polymerization of monodisperse polymer beads

Crosslinked polystyrene beads were prepared at low swelling ratios by one-step swelling and polymerization method. Pore size of the beads was observed based on the GPC calibration curves. It is found that: (1) the pore size increases as the swelling ratio decreases; (2) when a good solvent is used as the porogen the pore size increases with the crosslinking monomer content; and (3) at high crosslinking monomer content the pore size does not depend on the porogen solubility. The effects are discussed in terms of polymer miscibility, including phase separation between the seed and bead polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3270–3277, 2000

Molecular dynamics studies of the structure and properties of polymer nano-particles

Recently, we have developed an experimental technique for the production of monodisperse polymer particles with arbitrary size and composition. In order to examine the behavior and properties of polymer particles in the micron and submicron size, computational simulations were employed. A molecular dynamics based method for the generation and analysis of polymeric nano-particles is described in this article. This technique is used to study the dynamics as well as the behavior and the structural, thermal, and mechanical properties of nano-meter scale polymer particles.

Phase transitions of colloid-polymer systems in two dimensions.

Phase transitions of systems consisting of colloidal particles and non-adsorbing polymer in a solvent are studied theoretically in two dimensions. The colloids are modeled as hard spheres and the polymer as an ideal gas. The imbalance in osmotic pressure induced by the depletion effect gives rise to an effective attraction tail for the colloid-colloid interaction. For a monodisperse polymer, liquid-liquid separation is predicted to occur for appropriate colloid concentrations when the ratio s of the radius of gyration of the polymer to the radius of the colloidal particle is greater than 0.31, while solid-liquid separation is predicted to occur for all colloid concentrations when s is smaller than 0.31. Polydispersity of polymer is found to increase the extent of liquid-liquid coexistence, and when the average s is smaller than 0.31, and for appropriate colloid concentrations, liquid-liquid coexistence occurs provided the polymer size distribution is broad enough. Partitioning and size distribution of polymer in coexisting phases are also predicted.

Inverse size-exclusion chromatography for distributed pore and solute sizes

The pore-size distribution (PSD) of a liquid-saturated porous medium can be determined by inverse size-exclusion chromatography (ISEC) under suitable conditions. To quantify the limitations of longitudinal dispersion, intraparticle diffusion, and adsorption, we present a mathematical model for chromatographic procedures with polydisperse solutes. Results are applicable to either inverse or ordinary SEC. The conventional ISEC procedure with monodisperse polymer standards is a special case of the general development. Chromatographic responses for polydisperse solutes permit determination of the pore-size distribution by a deconvolution procedure if adsorption is negligible.

Effects of polymer molecular weight and temperature on case II transport

We investigated the effects of polymer molecular weight and temperature on Case II transport in the poly(methyl methacrylate)/methanol (PMMA/MeOH) system by a laser interferometric technique, using monodisperse polymer samples. Both the induction process and the steady-state front propagation were investigated. The data gave the volume fraction of MeOH in the swollen layer behind the moving front, ϕ, the steady state front speed, υ, and the characteristic induction time, tind. Values of ϕ separated into two groups, independent of molecular weight within each group. Significantly lower values of ϕ were found for polymers with molecular weight above the critical threshold for entanglement which can be explained by unrelaxed entanglements in the swollen layer. The Case II front velocity was independent of molecular weight for molecular weights at, or above, the critical weight for entanglement, suggesting that anelastic deformation processes other than simple viscous flow control the front propagation. Analysis of induction time data shows that the film surface properties differ from those of the bulk. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3159–3171, 1999

Another way to view the chain conformation broadening of the line-width distribution measured in dynamic light scattering

In dynamic laser light scattering (LLS), for a given plydisperse sample, a line-width distribution G(Γ) or the translational diffusion coefficient distributionG(D) can be obtained from the measured time correlation function. For rigid colloid particles,G(Γ) can be directly related to the hydrodynamic size distribution. However, for flexible polymer chains, G (Γ) depends not only on the chain length distribution, but also on the relaxation of the chain conformation; that is, even for a monodisperse polymer sample there still exists a chain conformation distribution. If the time scale of the chain conformation relaxation is comparable to that of the translational diffusion, such as in the case of a very long polymer chain, the conformation relaxation might lead to an additional broadening in G(Γ). This ‘conformation broadening’ has been directly observed for the first time by comparing twoG(Γ)s obtained from a ply(N-iso-propyl-acrylamide) solution at ~25°C: and ~ 32°C at which the solution is thermodynamically stable, where the fact is utilized that the PNIPAM chain can change from an extended and flexible coil at ~25°C into a highly collapsed and compact globule at ~ 32°C at which pint the polymer chain conformation distribution has diminished.

Analysis of the Diffusion in Pseudobinary Systems: Applications of Gouy Interferometry Parameters to Polydisperse Systems

The theory of diffusion in n-component systems has been applied to study the mutual diffusion of polydisperse polymeric systems. General relations for n-component systems have been obtained for the experimental Gouy parameters, DA and Q0. Through the use of the Flory equation for diffusion coefficients of monodisperse polymers, the expressions of DA and Q0 at infinite dilution, and , for a general molecular weight distribution have been obtained. These relations have been used to analyze the effect of polydispersity on Gouy diffusion parameters, and the relative information content of is stressed. A procedure is suggested to determine the molecular weight and to estimate the results of the fractionation through the Gouy interferometry. The results of this analysis have been applied to polyethyleneglycol, polyacrylic acid, and sodium polyacrylate diffusion data.

PREPARATION OF MONODISPERSE POLYSTYRENE PARTICLES BY RADIATION-INDUCED DISPERSION POLYMERIZATION

ABSTRACT Monodisperse microspheres of polystyrene with diameters in the size range I -2.2(μm) were prepared by the radiation-induced dispersion polymerization. The polystyrene microspheres by radiation-induced in the presence of co- solvent (DMSO-H2) was investigated as functions of various factors such as irradiation time, irradiation dose rate, the amount of water and on or not stirring et al. The number of the nuclei produced in the early stage of the polymerization was found to be constant during the remainder of the polymerization. The nuclei grow to be monodisperse polymer particles without aggregation under appropriate conditions, This is attributed to the low mobility of the growing polymer particles.

Penetration/release behaviors of various solvents into/from micron-sized monodispersed hollow polymer particles

The penetration/release behavior of various solvents into/from the hollow of micron-sized monodispersed cross-linked polystyrene (PS)/polydivinylbenzene (PDVB) (1/5.5, w/w) composite particle was examined. The hollow particles were produced by seeded polymerization utilizing the dynamic swelling method which the authors proposed earlier. The penetration into the hollow was affected by viscosity of the solvents and its affinity for the base polymers. Toluene saved in the hollow was released slowly. These results suggest that there is a possibility to apply such hollow particles as a controlled release material.

Single stage polymerization technique for producing monodisperse micron-size polymer particles

A single stage polymerization method for producing micron-size polymer particles is proposed. This method is based on soapfree emulsion polymerization in which the aggregation and dispersion stability of polymer particles in the course of the reaction is controlled by the addition of ionic surfactants to the reaction system. The validity of the present method was examined by studying the polymerization of styrene. The selection of suitable reaction conditions produced monodisperse micron-size polystyrene particles that were six times as large as particles produced without the addition of surfactant.

Thermodynamics for the preparation of micron-sized, monodispersed highly monomer-`adsorbed' polymer particles utilizing the dynamic swelling method

In previous articles, micron-sized monodispersed composite polymer particles were produced by seeded polymerizations for highly monomer-swollen polymer particles, in which the seed particle dissolves, prepared by the dynamic swelling method (DSM) proposed by the authors. This article discusses theoretically the thermodynamic background of DSM with seed particle which does not dissolve in monomer. It was clarified that the preparation of highly monomer-`adsorbed' polymer particles by DSM can be reasonably explained from the viewpoint of thermodynamic treatment under equilibrium and kinetic control states.

Synthesis of greater than 10-?m-sized, monodispersed polymer particles by one-step seeded polymerization for highly monomer-swollen polymer particles prepared utilizing the dynamic swelling method

The thermodynamic simulation under the kinetic control state indicates that 1.77-µm-sized monodispersed polystyrene (PS) particles can absorb 500 times the amount of the styrene monomer with keeping the monodispersity by the “dynamic swelling method” (DSM) which the authors proposed in 1991. Actually, about 14.1-µm-sized monodispersed styrene-swollen PS particles in which PS seed particles absorbed 500 times the amount of styrene monomer were successfully prepared utilizing DSM. By one-step seeded polymerization for the dispersion of the swollen particles at 30°C for 48 h with the 2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile) initiator, 13.1-µm-sized monodispersed PS particles were produced. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 278–285, 1999

Synthesis and Characterization of Highly Cross-Linked, Monodisperse Core−Shell and Inverted Core−Shell Colloidal Particles. Polystyrene/Poly(tert-butyl Acrylate) Core−Shell and Inverse Core−Shell Particles

We report on the synthesis of nearly monodisperse phase-separated polymer latexes with a well-defined core−shell morphology. Styrene/diisopropenylbenzene and tert-butyl acrylate/ethylene glylcol-diacrylate were used for either the core or shell of the composite microgel particles. A major concern of the paper is the detailed characterization of the core−shell and inverse core−shell particles by static and dynamic light scattering, transmission electron microscopy, solid-state NMR, and the analytical ultracentrifuge. The effect of the cross-linking agent on the final phase-separated morphology is discussed and compared with theoretical predictions.