tailieunhanh - The Estimation of Mechanical Properties of Polymers from Molecular Structure

The internal elements of a valve are collectively referred to as a valve's trim. The trim typically includes a disk, seat, stem, and sleeves needed to guide the stem. A valve's performance is determined by the disk and seat interface and the relation of the disk position to the seat. Because of the trim, basic motions and flow control are possible. In rotational motion trim designs, the disk slides closely past the seat to produce a change in flow opening. In linear motion trim designs, the disk lifts perpendicularly away from the seat so that an annular orifice appears | The Estimation of Mechanical Properties of Polymers from Molecular structure J. T. SEITZ The Dow Chemical Co. Central Research 1702 Building Midland Michigan 48674 SYNOPSIS The use of semiempirical and empirical relationships have been developed to estimate the mechanical properties of polymeric materials. Based on these relationships properties can be calculated from only five basic molecular properties. They are the molecular weight van der Waals volume the length and number of rotational bonds in the repeat unit as well as the Tg of the polymer. Since these are fundamental molecular properties they can be obtained from either purely theoretical calculations or from group contributions. The use of these techniques by polymer chemists can provide a screening technique that will significantly diminish their bench time so that they may pursue more creatively the design of new polymeric materials. 1993 John Wiley Sons Inc. 1. INTRODUCTION The purpose of this paper was to give polymer chemists a technique for estimating the important mechanical properties of a material from its molecular structure. Hopefully this will provide a screening tool that will significantly diminish their bench time so that they may pursue more creatively the design of new polymeric materials. The important practical applications of polymers are generally determined by a combination of heat resistance stiffness strength and cost in short the engineering properties of a material. Other properties may be of importance but if a polymer does not have a balance of these properties its chances for commercial success are very limited. To a large extent these properties can be associated on the molecular scale with the cohesive forces the molecular size and the chain mobility. The approach taken here is to relate molecular properties of the repeat unit to the properties of the polymer. Repeat unit properties can be obtained from group additivity or by simple calculations. In the usual group .

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