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 x 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 ([alpha](589)(25)) for Ph-PLLA (-38 deg dm(-1) g(-1) cm(3) was much lower than that of [alpha](589)(25) for 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 (Delta E-td) for Ph-PLLA (200 kJ mol(-1)) was higher than that for PLLA (158 kJ mol-1). The Delta E-td for the copolymers increased with an increase in L-phenyllactyl unit content. (C) 2008 Wiley Periodicals, Inc. J Appl Poly, Sci 110: 3954-3962, 2008