Journal of Polymer Science: Polymer Symposia最新文献

The dynamics of polymers are investigated in the regime of high molecular weight and high concentration using Monte Carlo dynamics. The lattice model used is described, and the idealizations used in this and other models are discussed. The results are presented and compared with the results of previous simulations.

Moderately concentrated polymer solutions are described as a suspension of interacting harmonic dumbbells. The interaction is treated in a mean field approximation. In the framework of this model the exact conformational distribution function for transversal shear flow is obtained. The shear viscosity and the first normal stress coefficient show the typical non-Newtonian form with a distinct power law behavior after the onset of shear rate dependence.

A review is presented of research on several aspects of the dynamics of conformational transitions in polymers. Brownian dynamics computer simulations of polymer chains show that transitions occur frequently in a correlated fashion involving cranklike counterrotation of two parallel bonds. Theoretical analysis brings out the importance of such counterrotations in creating a localized mode by which the transition can proceed without excessive motion of the whole molecule. The correlated motions are reflected in time correlation functions, which take on a character reflecting diffusion of the information about the initial state. Finally, several experiments are cited that can be explained on the basis of this picture of the mechanism of con formation a! transitions.

The swelling capacity of aqueous dispersions of particles (or droplets) containing a relatively low molecular weight, highly water-insoluble compound (Y) may be more than a thousand times higher than that of particles consisting of polymer only. The rate, and also the degree of swelling, may furthermore be increased by having the swelling substance, which usually is a low molecular weight, slightly water soluble substance, present in a finely dispersed form. A two-step swelling process has been described. In a first step, relatively small monodisperse polymer particles are swollen with a component Y and then with monomer or monomer mixtures, followed by polymerization. The method allows preparation of highly monodisperse particles of more than 50 μm diameter with a standard deviation of less than 2%. The particles may be prepared as core and shell particles of different density and with various surface layers, or as macroporous particles. The new particles have found application as standards in immunoassays and, most important up to now, in liquid chromatography. An extension of the process allows the production of monodisperse magnetizable particles which have found application in cell separation of cancer cells from normal cells.

In this talk, highlights and an interconnected thread of ideas will be presented in relation to the following specific areas of polyelectrolyte research: (1) the development of ion retardation resins, which are “snake-cage” or semi-interpenetrating polyelectrolyte systems that absorb ionic species reversibly; (2) the synthesis of specially and chelating ion exchange resins, by overcoming barriers to polymer reactivity; (3) reactive sulfonium monomers and polymers, in relation to coatings; (4) the enhancement, by chain stiffening, of the viscosifying effect of high molecular weight polyelectrolytes, in relation to improved water-flooding of oil wells. In the talk, the qualitative importance of the factors given in the title will be emphasized, and the influence of the work of Turner Alfrey will be illustrated.

Homogeneous nucleation temperatures for polystyrene/benzene solutions up to 60 wt% polymer have been measured. For polymer molecular weights from 17,500 to 100,000, homogeneous nucleation temperatures increase with increasing concentration from 226°C for pure benzene to 260°C for 60 wt% polymer. The experimental results have been compared to the predictions of homogeneous nucleation theory. It is concluded that for these solutions polymers affect the nucleation process principally through their effect on surface tension and solvent vapor pressure. For polystyrene solutions of molecular weight 600,000 or greater, a significant reduction in nucleation temperature was found. This phenomena appears to be caused by phase-separated domains in these high molecular weight solutions.

Experimental systems in which polymer fluids can be examined in different velocity fields are briefly described. The steady-state predictions of dilute solution theory are examined and their particular relevance to extensional flow experiments discussed. The observed flow behavior of broad-molecular-weight distribution polymer melts in different velocity fields is examined, particularly in relation to the apparent connections with the theoretical predictions of dilute solution behavior.

The rates of particle formation and growth during the earliest stages of the emulsion polymerization of several acrylic monomers have been studied as a function of surfactant concentration by means of the time-dependence of light scattering from the reaction mixtures. Investigated were methyl methacrylate, and methyl, ethyl, and butyl acrylates at concentrations of SDS surfactant from zero to several times the CMC. Under continuous photoinitiation, the Rayleigh scattering intensities rose rapidly with slopes that increased with decreasing SDS concentration. The more water-soluble the monomer, the more slowly was the rate of increase in scattering intensity.

We have investigated the details of phase separation dynamics in high-molecular-weight (polystyrene-PVME) polymer blends utilizing small angle light scattering techniques and have compared our results with the various theories, computer simulations, and phase separation dynamics in small molecule systems. Although linearized theories are consistent with many qualitative features of phase separation dynamics, they fail to provide quantitative accuracy. It appears that both nonlinear terms and hydrodynamic effects must be included to provide a quantitative description. Quantitative agreement between phase separation dynamics in small molecule systems and high-molecular-weight polymer blends is also reported.