Synthesis, physical properties, and crystallization of optically active poly(L‐phenyllactic acid) and poly(L‐phenyllactic acid‐co‐L‐lactic acid)

Abstract

AbstractOptically active poly(L‐phenyllactic acid) (Ph‐PLLA), poly(L‐lactic acid) (PLLA), and poly(L‐phenyllactic acid‐co‐L‐lactic acid) with weight‐average molecular weight exceeding 6 × 103 g mol−1 were successfully synthesized by acid catalyzed direct polycondensation of L‐phenyllactic acid and/or L‐lactic acid in the presence of 2.5–10 wt % of p‐toluenesulfonic acid. Their physical properties and crystallization behavior were investigated by differential scanning calorimetry, thermogravimetry, and polarimetry. The absolute value of specific optical rotation ([α]) for Ph‐PLLA (−38 deg dm−1 g−1 cm3) was much lower than that of [α] for PLLA (−150 deg dm−1 g−1 cm3), suggesting that the helical nature was reduced by incorporation of bulky phenyl group. PLLA was crystallizable during solvent evaporation, heating from room temperature, and cooling from the melt. Incorporation of a very low content of bulky phenyllactyl units even at 4 mol % suppressed the crystallization of L‐lactyl unit sequences during heating and cooling, though the copolymers were crystallizable for L‐phenylactyl units up to 6 mol % during solvent evaporation. The activation energy of thermal degradation (ΔEtd) for Ph‐PLLA (200 kJ mol−1) was higher than that for PLLA (158 kJ mol−1). The ΔEtd for the copolymers increased with an increase in L‐phenyllactyl unit content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008