Nucleation and crystallization of isotactic poly(propylene) droplets in animmiscible polystyrene matrix

In this work, isotactic poly(propylene) (iPP) was finely dispersed in immis cible atactic polystyrene (PS) matrices. When the dispersion obtained is fi ne enough (droplet size of approximately 1-2 mum), the iPP crystallizes in a fractionated fashion at temperatures between 104 and 42 degreesC. By appl ying a self-nucleation procedure we were able to corroborate that what caus es the fractionated crystallization in most droplets is the lack of highly active heterogeneous nuclei (i.e. those normally active at low supercooling s in the bulk polymer) in every droplet. When a sufficient amount of a comp atibilizer is used to obtain very small particle sizes and more homogeneous dispersions, the iPP crystallizes exclusively at a low temperature exother m that exhibits an onset at 51 degreesC and peaks at 46 degreesC, Wide-angl e X-ray diffraction measurements indicated that both the iPP in the bulk an d in dispersed droplets crystallized in the monoclinic alpha -phase, this e vidence may rule out the possibility that the crystalization observed at 46 degreesC is due to the formation of another crystal modification or a meso morphic phase as previously suggested in literature. The results presented in this work indicate that this low temperature exotherm may represent the dynamic crystallization during cooling of heterogeneity-free droplets that nucleate homogeneously at temperatures close to 51 degreesC.