Glass transition temperature of poly(d,l-lactic acid) of different molar mass

To evaluate the glass transition of poly(d,l-lactic acid)s (PDLLA), three PDLLA grades of different molar mass were analyzed by fast scanning calorimetry (FSC), on cooling at rates between 0.01 and 100,000 K/s. Poly(l-lactic acid) (PLLA) is used as a reference and measured at similar conditions as PDLLA, however, assuring the absence of crystallization. By using the Vogel–Fulcher–Tammann–Hesse (VFTH) equation to fit the glass-transition dynamics of PDLLA and PLLA, it is found that the Vogel temperatures of PDLLA and PLLA are essentially the same. In addition, the dependencies of the glass transition temperature on the molar mass of PDLLA and PLLA are evaluated. The glass transition temperatures of PDLLA and PLLA of infinite molar mass are the same, suggesting that the stereoisomerism does not influence the glass transition dynamics.