Enthalpy relaxations in polymer blends and block copolymers:Influence of domain size

It is now well known that enthalpy relaxation measurements can be used to establish polymer-polymer blend phase behavior when the glass transition temperatures of the two polymers are virtually coincident. In the most simple cases, the aging kinetics of an immiscible blend will be representative of the pure polymers superimposed upon each other. However, in many cases the situation is more complicated because of the presence of interface material. In this paper the relation between enthalpy recovery peak separation, domain size and interface thickness is considered. The discussion is based on relaxation experiments involving di-block copolymers of styrene and 2-vinyl pyridine, blends of polystyrene and poly(2-vinyl pyridine) and blends of poly(vinyl chloride) and poly(isopropyl methacrylate). If the amount of material in the interface is too large due to either a small average domain size or a thick interface no peak separation will occur. The first situation is found for the microphase separated block copolymer system whereas the second possibility occurs for blends of polymers which are on the verge of miscibility like poly(vinyl chloride) and poly(isopropyl methacrylate)