Background: The nature of phase transitions and apparently irreversible phase homogenization upon heating in blends of biodegradable poly(L-lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were proven using differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy and 1H NMR spectroscopy. The complex phase behaviour in this blend system is puzzling and is a matter of debate; this study attempts to clarify the true nature of the phase behaviour. Results: A PMMA/PLLA blend is immiscible at ambient temperature but can become miscible upon heating to higher temperatures with an upper critical solution temperature (UCST) at 230°C. The blends, upon rapid quenching from the UCST, can be frozen into a quasi-miscible state. In this state, the interaction strength was determined to be X12 = -0.15 to -0.19, indicating relatively weak interactions between the PLLA ester and PMMA acrylic carbonyl groups. Conclusion: The absence of chemical exchange reactions above the UCST and phase reversibility back to the original phase separation morphology, assisted by solvent re-dissolution, in the heat-homogenized PLLA/PMMA blend was shown. Verification of UCST behaviour, phase diagrams and solvent-assisted phase reversibility were experimentally demonstrated in PMMA/PLLA blends.
All Science Journal Classification (ASJC) codes
- Polymers and Plastics
- Organic Chemistry
- Materials Chemistry