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Characterization of single-phase and phase-separating polymer blends by rheology, optical and electron microscopy, and solid state NMR

Ioannis Polios, University of Massachusetts Amherst


Miscible and phase-separated blends are of great practical interest because a range of useful materials can be produced by blending existing polymers. The relation between rheology and time dependent morphology of a phase separating binary blend of polystyrene and poly(vinyl methyl ether) was investigated by heating a sample from the single phase (at 90 $\sp\circ$C) into the two phase regime (at 124$\sp\circ$C, 16 K above the LCST) and maintaining its temperature there while measuring the evolution of the dynamic moduli G$\sp\prime$ and G$\sp\prime\sp\prime$. The morphology was observed on length scales from 1 mm down to 1 nm by conventional optical microscopy combined with digital image analysis, Hoffman modulation microscopy, TEM, and WISE NMR with spin diffusion. NMR shows that major compositional changes occur mostly in the first 20 min and then the composition remains constant at about 60:40 PS/PVME for the PS-rich matrix and 5:95 PS/PVME for the PVME-rich microdomains. The PVME-rich microdomains are separated by thin layers of the PS-rich phase which forms the matrix. On a larger scale, shape and geometry change during the entire experiment (42 h). The linear domain growth is consistent with the theories of Siggia and Doi-Ohta. The initial increase of the dynamic moduli is attributed to the formation of highly interconnected PVME-rich and PS-rich phases during spinodal decomposition. The subsequent decrease of the values of the dynamic moduli is considered to be the result of the loss of the interconnectivity between the two phases due to the break-up of the PS-rich phase network and the coalescence of the PVME-rich domains. The thermorheological behavior of binary model blends of polystyrene and poly(2, 6-dimethylphenylene oxide) is also examined. Their rheological properties were modeled based on parameters of the pure components. The pure components were treated as slightly polydisperse linear flexible polymers and the relaxation behavior of the blends was presented as the linear superposition of the relaxation behavior of the pure components while the parameters of our model were successfully correlated with the glass transition temperature of our blend samples.

Subject Area

Chemical engineering|Plastics

Recommended Citation

Polios, Ioannis, "Characterization of single-phase and phase-separating polymer blends by rheology, optical and electron microscopy, and solid state NMR" (1998). Doctoral Dissertations Available from Proquest. AAI9841911.