Nanoheterogeneities in PEO/PMMA blends: A modulated differential scanning calorimetry approach

Modulated differential scanning calorimetry has been carried out on melt-mi xed blends of poly(ethylene oxide)/atactic-poly(methyl methacrylate) (PEO/P MMA). Two PEO molecular weights have been used to prepare blends in the con centration range 10 to 80 wt % of PEO. Two glass transitions temperatures w ere observed for the fully amorphous blends, in the 10 to 30 wt % PEO range , using the differential of heat capacity with respect to temperature [dC(p )/dT] signal. The semicrystalline blends, 40, 60, and 80 wt % PEO, exhibite d melting of PEO crystallites and the PEO-rich phase glass transition at -3 0 to -50 degrees C. A second glass transition around 30 degrees C was detec ted for the 40 wt % PEO blend when a cooling run was carried out, because P EO crystallization was avoided under these conditions. Therefore, heterogen eous amorphous phases were observed not only for fully amorphous blends, bu t also for semicrystalline ones. Further analysis of the dC(p)/dT signal, o btained from the MTDSC experiments by fitting with Gaussian curves, showed that there is an interphase that varies in amount between 10 to 50 wt %. Co rrelation of the MTDSC observations with NMR spectroscopy and SAXS/SANS lit erature results are discussed. (C) 2000 John Wiley & Sons, Inc.