AbstractThe orientation of crystallites grown isothermally in several drawntrans‐polychloroprene networks is studied as a function of crystallization temperaturetx, degree of crystallinity ω, and elongation ratio α. The orientation distribution is particularly simple for this polymer since the crystallographiccaxis (chain axis) orients preferentially along the stretching direction, whileaandbare randomly arranged aboutc. Hence the parameter cos2χcadequately characterizes the distribution, where χcis the angle between thecaxis and the fiber axis, and the average is taken over all crystallites. A treatment due to Krigbaum and Roe is utilized to obtain values ofv(the number of statistical segments comprising the crystallization nucleus of critical size) through comparison of the average orientation of crystallites and amorphous statistical segments. The behavior observed falls into two categories. First, if the initial amorphous network is well oriented, 〈cos2χc〉 is independent of crystallinity during both crystallization and melting, andvvaries withtz(or the degree of supercooling) as predicted by nucleation theory. If different networks are to have the same crystallite orientation distribution, they must not only be crystallized at the same supercooling, but must also have the same distribution of amorphous segment orientations. Both the relative elongation and the network crosslink density affect the latter distribution. Next, we consider the second category. If the initial amorphous orientation is poor, 〈cos2χc〉 decreases linearly during crystallization and increases along approximately the same path during melting. Further, 〈cos2χc〉 for a giventzyieldsvvalues which are too large. These two behaviors can be explained if, in the former case, nucleation involves the best oriented statistical segments of all network chains, while in the latter there is a selection according to the chain displacement vector orientation. Thus, if the amorphous orientation is poor, both the orientation and thermodynamic stability of the crystallites decreases with further crystallization. If this decreased stability is reflected in shorter fold lengths, the reversible variation of long period spacing with temperature reported earlier for an oriented polychloroprene network can also be explained as a preferen