Effects of Chain Configuration on UCST Behavior in Blends of Poly(L-lactic acid) with Tactic Poly(methyl methacrylate)s

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 similar to 250 degrees 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 degrees 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 T-g-composition relationship for the sPMMA/PLLA blend fits well with the Gordon-Taylor T-g model with k = 0.15 and the blend's T-m(0) leads to chi(12) = -0.26 for the UCST-quenched sPMMA/PLLA blend. Both parameters (k and chi) 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. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2355-2369, 2008