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In these three decades of progress, thermoplastic elastomers have risen in 1987 to a position of tenth in the order of commercial thermoplastic sales in the U.S.A., with a growth rate, 1986–1987, of 9.7%. It is very probable that the quantity shown for 1987 sales, 441 million pounds, is low, since it is well known that the largest producer of styrenic TPEs does not report offtake data. Much of the styrenic TPE goes to the adhesive industry, which also is very secretive in regard to materials consumption information. Thus, the 1986–1987 reported growth rate of 9.7% is on the low side. Another indicator of progress in the growth of TPEs has been illustrated by the number of product introductions from January 1986 to June 1987. During that period, TPEs led the major thermoplastics with the introduction of 270 new product types, and the nylons were a close second with 250. A third estimate of the explosive growth in TPEs may be seen in Table V which lists the number of manufacturers of TPEs in 1975, 1985, and 1987, increasing from 10 to 28 to 50. To summarize, the present thermoplastic elastomers, now high-volume commercial products, had roots in the chemistry and technology of polymers in the 1920's. Throughout the history of the “Roots” period one can detect precursor events from which several TPEs could have been foreseen. In each of the three decades of progress, major advances were made in the technology, physical properties, availability, and utilization of TPEs. The numbers of these increased in each succeeding period. Several paradigms appear in this review, for example: 1. The triblock styrene-diene A-B-A copolymers, morphology, and elastomeric character, in the first decade. 2. The copolyesters with (A−B)n morphology and greatly enhanced physical properties in the second decade. 3. The dynamically-vulcanized blends of EPDM and PP, followed in time by the concept of compatibilization to permit practical blends of NBR and PP in the third decade. Throughout these periods, growth was catalyzed by the favorable economics of manufacturing finished elastomeric products via low-cost thermoplastic processing techniques as compared with thermoset rubber processes. The reuse of scrap also provided a major incentive. In addition to these, the concept of component integration is now showing a path toward even more cost reduction incentives. New applicational areas continue to appear. One of these, blending relatively small amounts of TPEs with existing large volume thermoplastics, promises to provide extremely large offtakes of TPEs in the next decade. I am sure that the numbers of papers presented in symposia at meetings of the Rubber Division of the American Chemical Society confirm the continued explosive growth of TPEs we have seen in these past three decades.

The intrinsic "vistex" viscosities of several series of butadiene–styrene copolymers of varying conversion and average molecular weight, dissolved directly from the latex in the vistex solvent mixture (toluene–isopropanol, 80/20 by volume), have been investigated and compared with the intrinsic viscosities of the corresponding coagulated, dried polymers dissolved in toluene. The intrinsic viscosity in toluene, [η]T, is related to the intrinsic vistex viscosity, [η]V, in toluene–isopropanol by the equation:—[Formula: see text]Hence, viscosity average molecular weight may be calculated from vistex measurements.A further development of the method has shown that, once the latex is dissolved in the vistex solvent, the solution may be diluted, within certain denned limits, by the addition of pure solvent (toluene) to obtain the several levels of concentration of polymer required for the determination of intrinsic viscosity. It is then possible, by extrapolation to zero concentration of polymer, to obtain a value for the intrinsic viscosity that is equal to the conventional intrinsic viscosity of the polymer in pure solvent after coagulation and drying under very mild conditions. The viscosity characteristics of butadiene–styrene copolymers of varying conversion appear to be represented, at conversions below the gel point, by the equation,[Formula: see text]where β′ and n are constants of the order of 0.25 and 1 for solutions in toluene and 0.1 and 2.5 respectively for vistex solutions. Distinct changes in β and/or n have been found at conversions in the region of and beyond the gel point.

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An original ball-drop impact apparatus has bee11 consiructed and used to test the sensitivities of dextrin lead azide and mercury fulminate to mechanical Impact. Ball masses artd heights were both varied. Both the net kinetic energy and the change of nlomentuIn gave contin~~ous functions with the percentage of detonations. Con~parisons of the absolute values of the net kinetic energy and the change of momentum with another reported in the literature suggest that momentum is the more important factor in determining the probability of detonation. Values for the momenturn a t 50% detonatior~s for lead azide and mercury fulminate are 4.6 X 10' and 2.6 X lo4 c.g.s. units, respectively, with an area of contact of about 0.08 cm.? The corresponding times of impact were found to be ahout 2.2 X lo-' and 1.9 X 10-"ec.The question of whether the probability of the detonation of an initiator explosive is chiefly determined by the kinetic energy or the momentum of the impacting mass is of theoretical interest in interpreting the process of detonation by impact (8). In their earlier work, Taylor and Weale (9) suggest that kinetic energy is the important factor, although in 1938 (10) they introduce experiments and calculations based on momentum. Taylor and Weale do not mention the rebound of the steel balls used in their impact tests, although the measurement of rebound was introduced decades ago (referred to in Ref. 11). Powell, Skelly, and Ubbelohde (8) measured the momenta and kinetic energies of impact for mercury fulminate and lead styphnate. In their calculations, they assumed without measurement a definite value for the coefficient of restitution of the impacting mass. In the present work, some measurements of the net kinetic energy, change of momentum (hereinafter called impulse), and time of impact for the initiator explosives mercury fulminate and lead azide are reported. The time measurements allowed estimations to be made of the forces involved and these were found to be comparable with those found by Taylor and Weale (10) by an entirely independent method. EXPERIMENTAL MaterialsDextrin lead azide was prepared from sodium azide which had been recrystallized from a water-acetone mixture. Separate 50 ml. aqueous solutions containing 4 gm. sodium azide and 10.2 gm. lead nitrate C.P. were simultaneously added from burettes (delivery time-134 sec.) into 250 ml. of 0.5% aqueous solution of dextrin. Microscopic examination showed that the crystals of lead azide were of the same form as those prepared by Lowndes (6).