HE important observation, made by Katz ( 6 ) in 1925 using T x-ray diffraction technique, showed that the mere stretching of crude or soft vulcanized Hevea rubber caused a t least a portion of the polymer to undergo crystallization. This and the subsequent experiments of Hock ( 4 ) emphasized the point that ~uccesaful attempts to synthesize a polymer resembling Hevea rubber mould have to take regularity into account. The situation is complicated in isoprene polymers by the variety of ways the monomer can enter the growing polymer chain.The four isomeric forms of polyisoprene are shown in Figure 1.Since head-to-tail orientations must be considered because of the asymmetry of the isoprene molecule, there are eight possible arrangements of the units that can occur in polymerized isoprene. Sodium, potassium, emulsion, and alfin polyisoprenes have been shown to contain all four forms of the repeating units (8). All of these uncured polymers have poor tack and their pure gum vulcanizates shorn poor physical properties. They do not crystallize when stretched or cooled. It has long been recognized that polymers of conjugated hydrocarbon dienes would have to be very regular in structure before their properties would approach those of Hevea rubber.Looking back over the last 15 to 20 years, there has been a elow development, almost iniperceptible at first, of catalyst systems m-hich produce polymers that in some degree shox-an oriented structure. This orientation could result if the monomer, during the propagation phase of the polymerization, is held in a definite position with respect to the growing chain, as by cybotactic forces where polymerization is initiated a t the melting point of the monomer or as by adsorption of the monomer onto a solid surface-perhaps to the surface of the catalyst itself.The woik reported here deals primarily mith the properties of a rubber made by directed polymerization. POLYMER STRUCTURE AND PROPERTIESCatalyst. Catalyst systems, based on polyolefin information purchased from Karl Ziegler, hare been applied to isoprene mononler systems. and modifications have been developed such that either cis-1,4-polyisoprene or trans-l,4-polyisoprene can now be prepared at n 111 Infrared Absorption Spectra. The effect of one of these catalyst modifications was first recognized when a modified olefin polymerization yielded an isolable unstabilized rubbery component n~liich showed an infrared absorption spectrum (2-to 25micron range) almost identical to that of Hevea rubber except for peaks due to oxidation at 2.8, 5.6, and 5.8 microns and, additionally, a slightly higher intensity in the peak at 11.25 microns. Subsequent samples of this rubber, a cis-1,4-poly-I The B. F. Goodrich Go., Tire and Equipment Division, Akron, Ohio.isoprene, now called Ameripol SN, when protected by age resistors did not show these oxidation peaks (Figure 2).Infrared absorption spectra indicate low ma,ximum concentrations of 1,2-and 3,4-addition products in Bmeripol SN. For these two isomeric units the discrimination in the presen...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.