Effects of chain configuration on UCST behavior in blends of poly(L‐lactic acid) with tactic poly(methyl methacrylate)s

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 T g -composition relationship for the sPMMA/PLLA blend fits well with the Gordon-Taylor T g model with k ¼ 0.15 and the blend's T 0 m leads to v 12 ¼ À0.26 for the UCST-quenched sPMMA/PLLA blend. Both parameters (k and v) 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.

Tacticity in Vinyl Polymers

“…A more valid interpretation on the phase behavior in PLLA/PMMA blends has been recently offered by Li and Woo (40), and they have claimed that the blend systems of s-PMMA/PLLA and a-PMMA/PLLA are immiscible with an asymmetry-shaped upper critical solution temperature (UCST) behavior near 230-250 • C. On the other hand, an i-PMMA/PLLA blend remains immiscible up to thermal degradation without showing any transition to UCST upon heating. In addition to the phase behavior in blends, the morphology and nucleation density of PLLA crystals in tactic PMMA/PLLA blends are also affected by the critical temperature of melt treatment (T max ) as shown in Figure 2 (40). This figure shows POM micrographs of the spherulites of PLLA blended with various tactic PMMAs melt-crystallized at 130 • C from the temperature below UCST (row A) and above UCST (row B).…”

Properties of mineral filled poly(lactic acid)/poly(methyl methacrylate) blend

“…8 Another potential method is to blend PLA with other polymers having better thermal resistance. Nevertheless, miscibility between PLA and PMMA is not a straightforward issue and changes in preparation method 16,17 or in PMMA tacticity 18 can lead to different phase behaviors. However, these blends are immiscible and, in an immiscible blend, the glass-transition temperature of PLA remains unchanged.…”

Hydrolytic stability of polylactide and poly(methyl methacrylate) blends

“…Contradictory results were found for blends prepared in the melt state with some authors reporting a phase separation while others reported a single phase . One way to explain these different observations is that the blend has an upper critical solubilization temperature . Despite the effectiveness of melt mixing technique to obtain miscible blends, the increase in the molecular weight of the constituent polymers, that is, PLA and PMMA, has been shown to promote phase separation …”

“…31,32 One way to explain these different observations is that the blend has an upper critical solubilization temperature. 30,33 Despite the effectiveness of melt mixing technique to obtain miscible blends, the increase in the molecular weight of the constituent polymers, that is, PLA and PMMA, has been shown to promote phase separation. 28,29 The phase behavior of the blend may directly affect the hydrolysis phenomenon.…”