Sub-micrometer polyamide droplets dispersed in polyethylene: Dimensional stability above the melting point of polyethylene

Metallocene-catalyst polymerized ethylene-1-octene copolymers in which a polyamide 6 (PA6) is finely dispersed by means of a MA-grafted-polyethylene as compatibilizer show a non-conventional mechanical behavior at high temperatures. Once the ethylene-1-octene copolymer is melted the system still shows good mechanical properties and dimensional stability. Besides, due to the dispersed phase morphology of the system, so-called fractionated/homogeneous crystallization takes place (extra supercooling of around 50 °C compared to the bulk PA6 crystallization temperature) and the material can be processed in the same temperature range in which it later on will show good mechanical response. The explanation of this intriguing mechanical behavior is sought in the molecular architecture of the system and turns out to be related to the slower flow dynamics of the matrix chains in case of high enough molar mass. The slower dynamics is caused by an increase in entanglement density due to mixing/interactions between matrix chains and compatibilizer chains chemically attached to the droplets. The droplets thereby function as physical crosslinks.