Journal of Polymer Science: Polymer Symposia最新文献

There are two principal types of low temperature polycondensation processes: the two-phase process known as interfacial polycondensation and a single liquid phase process or solution polycondensation. Both procedures are widely used experimentally and have led to the preparation and evaluation of thousands of polymers. Types of polymers which are made commercially are polycarbonates, block elastomers, polyimides, and aromatic polyamides. Aromatic polyamides are produced commercially for two major end uses: (1) flame and heat resistant polymers in the form of fibers, films, molding powders, and papers, and (2) polymers with extended chains for high strength, high modulus fibers. The latter class of polymers give liquid crystalline solutions which make possible the direct formation of highly oriented, high strength fibers. Aramid fibers of this type are useful in cut resistant clothing, ballistics protection, asbestos replacement, ropes and cables, and reinforcement of resins and rubber. Continuing research on the low temperature procedures is leading to new variations and applications of these processes.

The synthesis and characterization of isobutylene/styrene tri- and H-block polymers, and the copolymerization of α,ω-styryl polyisobutylenes with N-vinyl pyrrolidone will be presented.

The concepts of reptation and the tube model have been successfully used to describe the dynamics of a system of entangled polymers. Attempts to apply this model have given rise to questions about the statistics of a polymer, represented by a lattice random walk, and its entanglement with an obstacle net. We have determined the number of ways such a walk can form unentangled closed loops of various types. If one reels in a general random walk from its ends, pulling out unentangled loop, one is left with the so-called primitive path, which is taken to represent the path of the tube. The probability that an N step random walk has a K step primitive path has been calculated. Asymptotic formulas for this probability are presented.

Given the numerous variables in composition, reaction conditions, and processing, the design of a polyurethane elastomer with a specified set of properties is indeed a challenging task. The control of characteristics such as heat stability, toughness, fatigue, and other key qualities requires a compendium of theoretical and experimental knowledge. Optimizing a single property, e.g., low temperature resiliency, can necessitate changes in composition that may compromise other important properties. Thus, to balance the entire system in order to meet the specification limits, much more than an empirical approach is needed to achieve the goal in a reasonable time. In this presentation, we will demonstrate that, by use of an array of sophisticated testing methods and carefully designed experiments combined with computer modeling, the tailoring of a segmented elastomer can be placed on a scientific basis. Key methods of characterization are dynamic mechanical spectroscopy, small angle X-ray scattering, electron microscopy, Fourier transform infrared, and differential scanning calorimetry. Special experiments included the systematic synthesis and testing of a wide range of model compounds. Optimum soft segment properties such as chain length and mobility were defined. Hard segments that are properly segregated and have high thermal and mechanical integrity were synthesized and characterized. These and related experiments have led us to a better understanding of the molecular mechanisms underlying the mechanical and thermal behavior of an elastomer. With this knowledge we can select molecular components and control phase relationships in building elastomers to meet end use requirements that demand maximum static and dynamic polymer properties.

In concentrated polymer latex systems where strong repulsive forces, either electrostatic or steric, exist between the particles ordering of the particles occurs. The structure formed can be examined by small angle neutron scattering and experiments indicate that the arrangement of the particles is liquid-like. Results are reported for a poly(-styrene) latex in an aqueous electrolyte solution and for a poly(-deuteromethyl methacrylate) latex, with the particles stabilised by poly-12-hydroxy stearic acid in dodecane.

We describe the results of a simulation of a model of a random chain embedded as a self-avoiding walk on a diamond lattice. The dynamic model is the same as Kirkwood's. The equation of motion method we use permits such functions as S(k, ω), the dynamic structure factor, to be calculated as easily as the density of states. We present results on the density of states and S(k, ω) for chains of 1000 monomers. The results illustrate a mechanism of harmonic self-stabilization of a chain, which we also discuss in physical terms. We believe that simulations of this type can be useful to experimentalists in relating spectral features to morphology.

The particle size distribution (PSD) of latex produced in a continuous reactor depends on recipe ingredients and reactor design and operation. Alfrey and co-workers developed theoretical models to predict PSDs for several cases. This work is briefly reviewed in the present paper, and more recent models are presented. The potential use of PSD data for the quantitative determination of kinetic parameters related to free radical desorption from latex particles is discussed.

This paper demonstrates how a recent formulation of fracture mechanics termed “Generalized Fracture Mechanics” is specially suited to the analysis of adhesive failure since it permits the separation of the interfacial component of adhesion from viscoelastic and other energy losses in the bulk of the adhesive (and/or adherends). The role of such losses can therefore be uniquely defined.

Experimental data on the rotation and translation of rigid rod macromolecules in the semi-dilute region are discussed in the terms of the Doi-Edwards theory. Available data indicate that the rotational diffusion coefficients vary approximately as the inverse concentration squared and the inverse length to a power between 7 and 8. The absolute value of the decrease of the rotational diffusion coefficient in the semidilute region relative to the infinite dilution value is about two orders of magnitude less than is predicted by the Doi-Edwards theory. Some possible explanations for these deviations include: