The effect of physical interactions on melt-phase homogenization of mixtures of poly( m-xylene adipamide) with aliphatic polyamides induced by interchange reactions

Abstract

Poly( m-xylene adipamide) (MXD6) was melt mixed at 290°C in a Brabender with the aliphatic polyamides: nylon-6,6, nylon-6,9, nylon-6,10, nylon-6,12 and nylon-12,12. MXD6 was found to be physically immiscible with each nylon- x, y; however, owing to interchange reactions during melt mixing, the mixtures eventually became one-phase. The time required for this reaction-induced phase homogenization was followed visually and by differential scanning calorimetry (loss of ability to crystallize and change in glass transition behaviour) and was found to increase significantly as the ratio of methylene to amide units, CH 2 NHCO ratio, in the aliphatic polyamide increased. The extent of reaction at the point of phase homogenization was determined by 1H nuclear magnetic resonance, and this, too, increased with the CH 2 NHCO ratio but not as much as the melt mixing time required for phase homogenization. These effects are attributed to the more unfavourable polymer-polymer interaction energy between MXD6 and nylon- x, y as the CH 2 NHCO ratio increases. This physical parameter is believed to influence the initial interfacial area (through the interfacial tension), the initial interfacial thickness and the length of the critical copolymer segment length for conversion of a microphase-separated block copolymer to a single-phase melt. All these factors influence the melt mixing time required for phase homogenization.