Morphology of model A/B(C-block-D) ternary blends and compatibilization of two immiscible homopolymers A and B with a C-block-D copolymer

The morphology of A/B/(C-block-D) ternary blends was investigated by transmission electron microscopy (TEM), and its implications in the compatibilization of two immiscible homopolymers A and B with a C-block-D copolymer are discussed. Emphasis is placed on the thermodynamic requirements and the role of order-disorder transition temperature (T-ODT) Of block copolymer for compatibilization. For the investigation, the following model ternary blends were prepared: (i) 63/27/10 PS/PB(P alpha MS-block-PI) with PS denoting polystyrene, PB denoting polybutadiene, P alpha MS denoting poly(alpha-methylstyrene), and PI denoting polyisoprene; (ii) 63/27/10 PPO/PP/(PS-block-PEB) with PPO denoting poly(phenylene oxide), PP denoting polypropylene, and FEB denoting poly(ethylene-co-l-butene); and (iii) 63/27/10 PMMA/PP/(P alpha MS-block-PI) with PMMA denoting poly(methyl methacrylate). Blend specimens were prepared by melt blending in a Mini-Max mixer at temperatures above and below the T-ODT of block copolymer. The TEM images of ternary blends showed a uniform distribution of(i) P alpha MS-block-PI layer on the surface of PB droplets dispersed in the PS matrix and (ii) PS-block-PEB layer on the surface of PP droplets dispersed in the PPO matrix only when melt blending was carried out at a temperature above the TODT of block copolymer. The formation of a uniform interphase between two immiscible homopolymers is attributed to the attractive thermodynamic interactions existing (i) between homopolymer PB and PI block in the 63/27/10 PS/PB/(P alpha MS-block-PI) ternary blend and (ii) between homopolymer PPO and PS block and between homopolymer PP and FEB block in the 63/27/10 PPO/PP/(PS-block-PEB) ternary blend. The present study indicates that the T-ODT Of block copolymer, in relation to melt blending temperature, determines whether the block copolymer can play the role of an effective compatibilizing agent even when thermodynamic requirements (attractive interactions) for compatibilization are Satisfied. Thus, we have concluded that attractive thermodynamic interactions done are not sufficient for compatibilization of two immiscible homopolymers unless the T-ODT of block copolymer is lower than melt blending temperature, because the viscosity of block copolymer in an ordered state (at T < T-ODT) is a few orders of magnitude higher than that in the disordered state (at T > T-ODT). That is, the mobility of block copolymer plays an important role in the compatibilization of two immiscible homopolymers.