Effects of Chain Tacticity or Chirality on Phase Behavior in Polymer Blends: Poly (methyl methacrylate), Polypropylene, and Poly (lactic acid)

摘要

Effects of chain configurations such as tacticity and chirality on phase behavior in blends composed of tactic/ chiral polymers have been of great interests. Issues in blends of polymers of the same chemical repeat unit but different tacticities/ chiralities were addressed by investigating on the phase behavior and interaction strength of blends based on polypropylene (PP) or poly (methyl methacrylate) (PMMA) of different tacticity configurations, i. e., atacticity (a-), syndiotacticity (s-), and isotacticity (i-), or poly (lactic acid) (PLA) of different chirality configurations. Although blends based on tactic polymers have been widely studied, there are on-going debates on interpretation on phase behavior (miscibility vs. UCST, or immiscibility) in such blends. The aPP/ iPP blend was shown to be miscible and possess a significantly negative value (-0.21). However, the sPP/ iPP and aPP/ sPP blends were found to be UCST systems (UCST=150~170℃) with the interaction parameters being nearly zero (-0.02 and -0.007, respectively, at Tm~180℃). On the other hand, phase behavior of counterpart blends based on tactic PMMA's is quite different from the trend of phase behavior seen in blends of tactic PP's. Difference in crystallinity in these blend systems may be at work. Factors and possible mechanisms will be discussed.