Liquid-Induced Crystallization of Poly( Ethylene-2,6-Naphthala te)
Previous studies devoted to the liquid-induced crystallization of polymers have primarily focused on poly(ethy1ene terephthalate) (PET). Thorough summaries of the morphology induced in PET by this type of crystallization exist in the literature.13 Recent work has also focused on the fundamental aspects of liquid induced cry~tallization.~~5 Some limited studies concerning the liquidinduced crystallization of initially amorphous poly(ethylene-2,6-naphthalate) (PEN) have indicated that this polymer can also readily be crystallized in certain liquids such as dioxane and methylene chloride, resulting in a particularly distinct spherulitic texture? In the present study, similar effects have been noted, along with observations concerning the time and temperature dependence of the formation of this spherulitic texture induced by dioxane and aniline liquid.
In the dioxane-PEN case, immersions at 24OC seem to result in the formation of distinct clusters of small spherulites (on the order of 1 to 2 jtm in diameter) on the film surface, clusters which appear to increase in number with increasing immersion time [see representative scanning electron micrograph (SEM) in Fig. 11. With increasing immersion temperature, these spherulitic clusters seem to become more evenly dispersed over the entire film surface until approximately 5OoC, at which temperature the sample appears to be uniformly covered with spherulitic material and cavitation is in evidence. The size of the spherulites themselves, however, apparently does not vary strongly with either immersion time or temperature. Polarized optical microscopy (OM) studies of these dioxane-treated materials show distinct maltese cross patterns, indicative of optically anisotropic spherulites.
Treatments of PEN in aniline liquid appear to result in distinct spherulitic structure rather uniformly dispersed over the entire sample surface at 24OC. Surface cavitation is also quite prevalent at this temperature. While amines are known to degrade polyesters, the degradation process requires a much longer time scale than was typically used in this study for the immersions of PEN in aniline.6 Increasing the immersion temperature (up to 75OC in our studies) has no significant effect on the spherulite size, but does seen to increase the uniformity of the surface cavitation. There does not appear to be any significant difference in the spherulite sizes produced by either dioxane or aniline in PEN. Figure 2 shows a representative SEM of the typical morphology induced in PEN by aniline. Also displayed in this figure is an SEM of a fracture surface of a PEN film immersed in aniline, demonstrating that this spherulitic structure extends into the bulk of the film as well. OM studies of these aniline-treated PEN films again verify that these materials have characteristic optically anisotropic spherulitic texture.
Fracture surfaces of PEN immersed in dioxane liquid at 24OC reveal an apparent front of liquid penetrating the polymer. For the PEN-dioxane system at 5OoC, a distinct permanent void is left Fig. 1. Representative SEM of the surface of an initially amorphous PEN f i l m immersed in dioxane liquid 90 min at 24OC.