JOURNAL OF MATERIALS SCIENCE 22 (1987) 523-531 Drawing of virgin ultrahigh molecular weight polyethylene: an alternative route to high strength/high modulus materials Part 2 Influence of polymerization temperature PAUL SMITH*, HENRI D. CHANZYt, BRUNO P. ROTZINGER§ E. L du Pont de Nemours and Company, Inc., Central Research and Development Department, Experimental Station, Wilmington, Delaware 19898, USA The synthesis of ultra-high molecular weight polyethylene films and the production of high strength/high modulus tapes and filaments drawn directly from the virgin polymer are described. The study particularly focuses on the effect of the polymerization temperature on the defor- mation behaviour of the virgin UHMW polyethylene films. These results are discussed within the framework of the entanglement concepts for deformation of weakly bonded macromol- ecules. The develop/nent of the room temperature Young's modulus and the tensile strength with draw ratio is presented and compared with modulus and tenacity/draw ratio relations observed for melt and solution crystallized polyethylene. 1. Introduction The structure and morphology of virgin, i.e. as- polymerized or nascent, crystallizable polymers has been a topic of interest in the 1960s [1-5]. In these early studies it was already recognized that under certain experimental conditions monomers may sim- ultaneously polymerize and crystallize into chain- extended structures. The mechanism underlying this interesting polymerization is reasonably well under- stood [1-5]. Macromolecules polymerized below their melting point, or, rather, dissolution temperature in the polymerization mixture, never experience the liberty of the completely liquid state; only a part of the growing molecule is "dissolved" in its surrounding medium. The macromolecules thus never adopt a random coil conformation and, important in relation to the present work, do not form many entanglements with neighbouring chains. The actual local tempera- ture, pressure and concentration determine how many segments of the growing chain are in the liquid state; that is true if the polymerization rate does not exceed the rate at which the polymer segments are incor- porated into the crystalline solid (schematically illus- trated in Fig. 1 for Ziegler-Natta type ethylene poly- merization). Thus it can readily be envisaged that under selected experimental conditions virgin poly- mers are produced in which the macromolecules exhibit a chain-extended and virtually "non-entangled" conformation. An example of a polymer produced commercially under such experimental conditions is poly(tetrafluorethylene) (PTFE) [6-8]. As a result, virgin PTFE has a number of properties that axe remarkable in comparison with those of the once- molten (and re-entangled) polymer: a very high crys- tallinity, high melting temperature [9] and most unusual flow characteristics of the solid polymer [10]. In Part 1 [11] we described preliminary results on drawing of virgin ultra-high molecular weight (UHMW) polyethylene as an alternative route to high strength fibres. The presented method dispenses with the elaborate dissolution, precipitation and solvent recovery procedures in the "gel-spinning" technique [12, 13] that axe necessary to untangle the long macro- molecules prior to tensile drawing [14]. The alternative virgin-polymer processing technique [11] relies on the synthesis of polyethylene under experimental con- ditions where the macromolecules are produced in a near non-entangled conformation. In view of the foregoing introductory remarks on virgin polymers, it is evident that the polymerization variables, such as temperature and pressure have a major effect on the conformation of the macromol- ecules produced and, therefore, on the properties of the as-polymerized polymer. In this paper we report on the effect of the polymerization temperature on the drawing characteristics of virgin UHMW polyethy- lene. 2. Experimental techniques Virgin polyethylene films were produced according to the technique that was previously described [I 1, 15, 16]. A rack containing six cleaned glass slides was immersed in a boiling solution of 1 mM freshly distilled VCI4 in dry n-heptane. After 10min a coating of fine VCI3 *Present address: University of California, Materials Program, Santa Barbara, California 93106, USA. ~i Permanent address: CERMAV (CNRS), BP 68, 38402 Saint Martin d'Heres, France. §Present address: Ciba-Geigy AG, Zentrales Forschungslaboratorium, CH-4002 Basel, Switzerland. 0022-2461/87 $03.00 + .12 © 1987 Chapman and Hall Ltd. 523