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J t is known that during processing of polystyrene thermoplastics by means of injection molding, molecular states of order are formed through shear and tensile forces which considerably influence the strength and deformation behavior of the moldings.1-6 Deformation of material caused by processing forces macromolecules into a high degree of order (orientation) and thereby a state of low entropy. This orientation represents the source of a force tending to bring system to a statistically more probable state i.e., higher entropy. This entropic-elastic power P, for one macromolecule is given6 by P, = KTh/Zaz(1)where K is the Boltzman constant, 2' is the absolute temperature, h is the distance between the ends of the chain, Z is the number of moving elements in the chain, and a is the length of the macromolecule. P, is thereby proportional to the degree of orientation (stretching) of the macromolecule and the absolute temperature. The relation (1) is valid only when plastic deformation of the macromolecules does not occur. At relatively low temperatures when the mobility of chains is at a minimum (there exist only vibration motions of atoms around equilibrium positions or motions of atom groups) this relatively weak force cannot lead to a decrease in the degree of order of the material.A decrease in degree of ordering is possible only after heating of the material above the glass transition temperature, when micro-brownian motion of segments of the polymer chains occurs. This makes possible application of the entropic-elastic power, and shrinkage of molecules and thereby deformation of the sample ensue.The method is based on following the course of deformation of the samples in dependence OIL temperature. In the case of uniasially oriented samples it is a measure of their deformat,ion length shrinkage s after tempering at. c:ertaiii t,emperat,ures.where lo is the distance between marks on sample before tempering and I is the distance between the same marks on sample after tempering. We took measurements of shrinkage in a Hoppler ultrathermostat with a 5 liter tempering vessel. We used ethylene glycol as working liquid which made possible measurements in the required temperature range (20-180°C) and ensured free contraction of samples during tempering (the samples floated on the surface of the liquid). I n order to prevent deformation of soft samples (an important factor during measurement at higher temperatures when plastic flow of material occurs), we took them from the bath by means of a special instrument. The test specimens used were of the type usually used for testing of mechanical properties of polymers. The samples were prepared by an injection- molding technique on a CSB 12-4-5 injection plunger machine a t a fusion chamber temperature of 190°C, theoretical molding pressure of 600 kp/cm2, and a form temperature of 3040°C. i.e., at conditions usual for preparation of test specimens from polystyrene thermoplastics.Measuring involves only putting marks on the test specimens and measuring the distance between ...

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