Cold crystallization behavior of polyamide 6 in PS-g-PA6 graft copolymers
Résumé
TEM micrographs show that the PA grafts of PS-g-PA6 graft copolymers, which are obtained directly by extracting homo-PA6 out from the homo-PA6/PS-g-PA6 blends, are in the form of wormlike structure. The wormlike PA6 domains can shrink into droplets after annealing at 250 °C for 15 min. The diameter of the droplet determined by TEM and SAXS is in the range of 50―60 nm. This article reports on a unique crys-tallization behavior of the PA6 grafts in PS-g-PA6 graft copolymers. In a DSC cooling scan, PA6 grafts do not crystallize from the melt with a cooling rate of 10 °C/min. However, there is a cold crystallization peak around 65 °C in the subsequent heating scan. This cold crystallization phenomenon, which has not yet been reported in the literature till now, follows well the homogeneous nucleation mechanism and is depressed at relatively slow cooling rates (2 °C/min) or even completely eliminated after annealing within a specific temperature range. It may be caused by the slow diffusion or transport rate of the less flexible PA6 grafts to the crystal fronts when crystallization takes place around its glass transition temperature.