ABSTRACT
In general, chemically different polymers are incompatible and exhibit macroscopic phase separation because of a vanishingly small mixing entropy of high molecular weight polymer chains, and the phase structure strongly inŽuences the slow dynamics of blends (Utracki, 1989). Nevertheless, a considerable number of polymer pairs are known to be miscible in given ranges of temperature and composition. In early studies, blends of such miscible polymers were considered to be more or less similar to blends of chemically identical polymers and were subjected to just a vague focus of research. However, at temperatures above the glass transition temperature, the local concentration of the components in miscible blends Žuctuates with time. In other words, the miscible blends are statically homogeneous but dynamically heterogeneous. This dynamic heterogeneity provides the miscible blends with a variety of unique features such as broad segmental relaxation/glass transition and signi†cant thermorheological complexity (failure of time-temperature superposition) for both local and global relaxation processes (see, e.g., Alegria et al., 1994; Chen et al., 2008, 2011, 2012; Chung et al., 1994; Colby and Lipson, 2005; Ediger et al., 2006; Haley and Lodge, 2005; Haley et al., 2003; Hirose et al., 2003, 2004; Kumar et al., 1996; Lodge and McLeish, 2000; Lutz et al., 2004; Miller et al., 1990; Miura et al., 2001; Pathak et al., 1998, 1999, 2004; Sakaguchi et al., 2005; Takada et al., 2008; Urakawa, 2004; Urakawa et al., 2001; Watanabe and Urakawa, 2009; Watanabe et al., 2007, 2011; Zhao et al., 2008, 2009).
