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

Optically 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 × 10 3 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]   589 25 ) for Ph‐PLLA (−38 deg dm −1 g −1 cm 3 ) was much lower than that of [α]   589 25for PLLA (−150 deg dm −1 g −1 cm 3 ), 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 (Δ E td ) for Ph‐PLLA (200 kJ mol −1 ) was higher than that for PLLA (158 kJ mol −1 ). The Δ E td for the copolymers increased with an increase in L ‐phenyllactyl unit content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008