Miscible blends containing poly(ethylene oxide) (PEO) have been examined over the entire composition range using differential scanning calorimetry to explore further the reported presence of two glass transitions. Three systems, poly(ethylene oxide)−dimethyl ether (PEO−DME)/poly(methyl methacrylate) (PMMA), PEO/poly(lactide) (PLA), and PEO/poly(vinyl acetate) (PVAc), were chosen in order to study the effects of end-group chemistry, annealing time, and crystallinity on the calorimetric behavior of the blends. The molecular weight of PEO was kept low to minimize the interference due to crystallization. Two distinct glass transitions were observed in the mid-composition range for all three systems. The glass transition temperatures varied smoothly with blend composition between the glass transition temperatures of the two homopolymer components. It was found that the self-concentration model describes the composition dependence of these glass transitions well. Further investigation on selected PEO/PVAc blends showed that annealing time and degree of crystallinity had a little effect on the glass transition behavior. These results confirm that the presence of two glass transitions should not necessarily be taken as an indication of immiscibility.
The linear viscoelastic properties of blends of poly(vinyl methyl ether) (PVME) with poly-(styrene) (PS), poly(styrene-stat-vinylphenol) (PSVPh) copolymers, and poly(vinylphenol) (PVPh) in different proportions were measured over a wide temperature range (0-160 °C). All blends were miscible over the temperature and composition ranges covered. The amount of hydrogen bonding was tuned by using copolymers with varying mole fractions of vinylphenol units (10%, 20%, and 50%). The time-temperature superposition principle (tTS) was used to create master curves from the rheological data. For some PS/PVME and PSVPh/PVME blends there was a clear failure of tTS. In contrast, tTS was successful for all the PVPh/ PVME blends and PSVPh/PVME blends with higher vinylphenol content, despite much higher differences between the component T g s. These results confirm that the dynamic response of two polymers can be effectively coupled in the presence of sufficient hydrogen-bonding interactions, whereby the temperature dependences of the two-component relaxation times become equivalent. By using an established model for predicting the extent of hydrogen bonding, the concentration of hydrogen bonds necessary to couple the dynamic behavior, as reflected by the success of tTS, was estimated. The size of the associated "control volume" is comparable to the Kuhn length.
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