Determining the Effectiveness of Polymer Blend Compatibilization by Multiblock Copolymers Formed in-situ via Melt Mixing

摘要

A great deal of theoretical and experimental work has been carried out on the compatibilization of immiscible blends of homopolymer pairs.1-5 Copolymers consisting of two monomers,each of which are miscible in one of the homopolymers of the blend,have been shown to result in a finer dispersion of the minor phase and increased interfacial strength. The copolymer promotes adhesion between the immiscible phases,reduces interfacial tension,and sterically hinders the minor phase droplets from recombining.6-8 Blends made industrially are often economically compatibilized by reactive extrusion using monofunctional reactive polymers to form a diblock copolymer in-situ.9 More recent thin film studies have shown that a premade multiblock copolymer is more effective at promoting adhesion between the two immiscible phases than a diblock due to the fact that the multiblock copolymer crosses the interface several times,forming stitches.5 However,premade multiblock copolymers are much more likely to be trapped in the bulk phase as micelles,as the critical micelle concentration decreases with increasing molecular weight.10 By reacting low molecular weight telechelics containing complementary end groups during processing to form larger multiblock copolymers at the biphasic interface,the formation of micelles in the bulk can be minimized. However,the choice of the telechelic molecular weight can be critical in the success of this scheme. The optimal telechelic molecular weight is a compromise between low molecular weight telechelics which may quickly approach the interface and have a high end group concentration,and high molecular weight telechelics which are more effective at suppressing coalescence by steric hindrance.8