Effects of chain configuration on UCST behavior in blends of poly(L‐lactic acid) with tactic poly(methyl methacrylate)s |
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Authors: | Shu‐Hsien Li Eamor M Woo |
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Institution: | Department of Chemical Engineering, National Cheng Kung University, Tainan 701‐01, Taiwan |
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Abstract: | Chain configuration influences phase behavior of blends of poly(methyl methacrylate) (PMMA) of different tactic configurations (syndiotacticity, isotacticity, or atacticity) with poly(L ‐lactic acid) (PLLA). Blends system of sPMMA/PLLA is immiscible with an asymmetry‐shaped UCST at ~250 °C. The phase behavior of the sPMMA/PLLA blend is similar to the aPMMA/PLLA blend that has been already proven in the previous work to exhibit similar UCST temperatures (230–250 °C) and asymmetry shapes in the UCST diagrams. On the other hand, the iPMMA/PLLA blend remains immiscible up to thermal degradation without showing any transition to UCST upon heating. The blend system with UCST, that is, sPMMA/PLLA, can be frozen in a state of miscibility by quenching to rapidly solidify from the homogeneous liquid at UCST, where the Tg‐composition relationship for the sPMMA/PLLA blend fits well with the Gordon‐Taylor Tg model with k = 0.15 and the blend's T leads to χ12 = ?0.26 for the UCST‐quenched sPMMA/PLLA blend. Both parameters (k and χ) as characterized for the frozen miscible blend suggest a relatively weak interaction between the two constituents (sPMMA and PLLA) in the blends. The interaction strength is likely not strong enough to maintain a thermodynamic miscibility when the blend is at ambient temperature or any lower temperatures below UCST. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2355–2369, 2008 |
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Keywords: | blending configuration differential scanning calorimetry (DSC) phase behavior phase diagram PLLA PMMA UCST |
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