The Role of the Order−Disorder Transition Temperature of Block Copolymer in the Compatibilization of Two Immiscible Homopolymers

Abstract

The important role that the order-disorder transition temperature (TODT) of a block copolymer plays in the compatibilization of two immiscible homopolymers is demonstrated, using the model ternary blend systems consisting of a polystyrene-block-polybutadiene (SB diblock) copolymer and two immiscible homopolymers, polystyrene (hPS) and polyisoprene (hPI). For the study, SB diblock copolymers having different microstructures were employed. We investigated via transmission electron microscopy (TEM) the morphology of the blends. We found that an SB diblock copolymer was very poorly distributed at the interface between hPS and hPI in an hPS/hPI/SB ternary blend when the specimen was annealed at a temperature below the T ODT of the block copolymer, while a more uniform distribution of the SB diblock copolymer was observed when a specimen was annealed at a temperature above its TODT. We have shown that the miscibility (or the interaction parameter) between the hPI and PB block in an SB diblock copolymer plays a decisive role in controlling the morphology at the interfaces between hPS and hPI. We conclude that a block copolymer must be designed, such that its TODT is below the targeted melt blending temperature, in order for the block copolymer to be able to act as an effective compatibilizing agent for two immiscible homopolymers. This conclusion is supported further by investigating the tensile properties and morphology of ternary blends consisting of polypropylene (PP), hPS, and polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene (SEBS triblock) copolymer (Kraton G1650), which were prepared by melt blending at 200 °C in a batch mixer. That is, little improvement in the tensile properties of the ternary blends was observed when Kraton G1650 was added to PP/hPS binary blends. This observation is explained by a very poor distribution, observed by TEM, of Kraton G1650 at the interface between PP and hPS in the ternary blend. This is attributed to the very high T ODT, estimated to be above 350 °C from currently held mean-field theory, of Kraton G1650 compared to the melt blending temperature employed.

Influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene and elastomer blends

“…This peak did not disappear in the temperature range in which the thermal cycles were performed. However, it will decrease in intensity and finally it will not be observed at the orderedisorder transition of the block copolymer at much higher temperature (around 350 C) [42]. Therefore, the crystallization of iPP in the iPP/ SEBS blends took place in the presence of styrenic domains which imposed an effect on these processes.…”

Morphology of compatibilized ternary blends of polypropylene, nylon 66, and polystyrene

“…The lowered viscosity of the melt could also have allowed more opportunity for the dispersed particles to contact one another, so coalescence could occur. The phenomenon of increasing particle size has also been seen with increasing compatibilizer [23,29].…”

Morphology and mechanical properties of polypropylene/polystyrene blends compatibilized with styrene–butadiene block copolymers

“…Chun and Han [9] proposed that the order–disorder transition temperature, T ODT , of a block copolymer strongly affects its compatibilization efficiency. They proposed that only in systems prepared at a temperature above a copolymer T ODT , the copolymer can show emulsification effect and form an “interphase” improving mechanical properties of the blend.…”