1742
W. J. BARNES, W. G. LUETZEL AND F. P . PRICE
Vol. 65
CRYSTALLIZATION OF POLY-(ETHYLENE OXIDE) IN BULK BY WILSONJ. BARNES, WILLIAM G. LUETZEL AND FRASER P. PRICE General Electric Research L.aboratory, Schenectady, New I'mk Received March 1 , 1961.
Measurements of spherulite growth rates and bulk crystallization rates have been made at a variety of temperatures on several Ioly-(ethylene oxide) polymers in the molecular weight range of 5000 to 30,000. Spherulite nucleation rates have been c a h l a t e d . It is found t h a t both the spherulite growth rates and the bulk crystallization rates have essentially the same temperature coefficient. This makes the spherulite nucleation rates essentially temperature independent. It is concluded that spherulite nucleation is a heterogeneous process. A theory of spherulite growth as a nucleation controlled process is presented. It is concluded that, if a constant nucleation rate per unit spherulite boundary is assumed, the growth of the crystallites comprising the spherulite is very rapid compared to their nucleation. This theory is applied to the data obtained and conclusions about the magnitude of some of the interfacial tensions are drawn.
Much of the current work on crystallization of synthetic high polymers is concerned with the investigation of tiny single crystals produced by precipit,ation from dilute solution. l - 8 Notwithstanding the intrinsic interest of these crystals, and notwithstanding the possibility that their study may ultimately lead us to a comprehension of the situation in bulk polymers, it is nevertheless fruitful to continue investigations of the crystallization of synthetic high polymers in bulk. The development of crystallinity in bulk polymers is intimately connected with the nucleation and growth of spherulitic structures. The majority of investigations of the crystallization process have been carried out using dilatometric technique^.^-^ In these cases the nucleation process and the growth process are inextricably intertwined. Only in relatively few instances7s8have microscopic observations of spherulite growth rate been combined with measurements of bulk crystallization rates to yield information on the rate of spherulite nucleation. In these instances it has been found that the temperature dependence of the bulk crystallization rate almost exactly equals the temperature dependence of the spherulite growth rate. Further these investigators show that, contrary to the conclusions of Mandelkern, et al.,6 the growth and crystallization rates have a dependence on the inverse first order and not on the inverse second order of the supercooling. This paper is concerned with the rate of spherulite nucleation and growth in poly-(ethylene oxide). This ma.teria1was chosen for investigation beoausc it melts in an easily accessible region, and it is readily available in a range of molecular weights. However the principal reason was that it appeared that it might be possible by following Hibbert's proceduree to prepare by stepwise synthesis, a series of monodisperse polyglycols of various molecular weights. The crystallization behavior of these materials both in bulk and from dilut,c solution was to be investigated. This preparative attempt has been notable only in its complete lack of twccess. The investigation described here (1) A. Keller, Makromol. Chem.. 34, 1 (1959). (2) A. Keller, Phil. Map.. 4, 21 (1957). (3) H. A. Stuart, Kolloid-Z.. 165, 3 (1959). (4) L. A . Wood and N. Bekkedahl. J . Appl. Phya.. 17, 362 (1946). (5) P. u'.Allen, Trans. Faraday Soc.. 48, 1178 (1952). (6) L. Mandelkern, F. A . Quinn. Jr.. and P. J. Flory. J . A p p l . Phys.. 46, S O (1954). (7) Von B. Kahle. 2. Wektrochem., 61, 1318 (1957). ( 8 ) Von 13. v. Falkai and H. A . Stuart, Kollmd-Z., 162, 138 (1959). (9) E . L. l,o>-elland I
