Poly(L-lactic acid) (PLLA) (-CH(CH3) -COO-)(n) is a biodegradable polymer, which exhibits many applications in the biomedical field and where thermoplastics are employed. A comprehensive study of the normal modes and their dispersion in PLLA using Wilson's GF matrix method as modified by Higgs is being reported. Assignments of calculated normal modes have been made and characteristic features of dispersion curves are discussed. Heat capacity has been calculated via density-of-states using Debye relation in the temperature range 10-250 K, which is in fairly good agreement with the experimental data. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48:175-182, 2010