Molecular Relaxation Mechanisms of Tyrosine-Derived Polycarbonates by Thermally Stimulated Depolarization Currents N. SUA ´ REZ, 1 E. LAREDO, 1 A. BELLO, 1 J. KOHN 2 1 Physics Department, Universidad Simo ´n Bolı ´var, Caracas, Venezuela 2 Department of Chemistry, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903 Received 12 January 1996; accepted 13 June 1996 ABSTRACT: A series of tyrosine-derived polycarbonates with different lengths ( 2 ° n ° 8 ) for the alkyl ester pendent chain were studied by measuring thermally stimulated depolarization currents ( TSDC ) . The observed spectra could be separated into three regions: the low-temperature zone with a broad, complex b band (80–240 K), the intermediate zone (250–300 K), and the high-temperature zone (300–400 K) with a sharp a peak. The application of direct signal analysis ( DSA ) to decompose the complex peaks into elementary processes led to the determination of the relaxation time distri- bution and temperature dependence of each process. The variation of the relaxation parameters as a function of the pendent chain length facilitated the tentative identifi- cation of the relaxation mechanisms responsible for the observed current peaks. It is proposed that as the temperature increases one observes, first, the individual motion of each polar group, then the concerted motion of the entire pendent chain, and, last, the movement of the polymer backbone.  1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1457 – 1466, 1997 Key words: polycarbonates; tyrosine; dielectric relaxations; TSDC; glass transition; biomaterial INTRODUCTION sulting in carbonate – amide copolymers pos- sessing an ester-linked pendent chain (Fig. 1). Tyrosine-derived polycarbonates are new degrad- Previous studies have confirmed that these mate- able polymers being investigated for medical ap- rials are generally biocompatible, possess favor- plications such as drug delivery and bone fixa- able physicomechanical properties, and can be tion. 1–4 These degradable polymers represent a fabricated readily into devices useful for medical specific example of pseudo-poly ( amino acid)s applications. 5,6 and, in this case, are derived from the polymeriza- Currently, the family of tyrosine-derived poly- tion of desaminotyrosyl – tyrosine alkyl esters re- carbonates comprises four polymers whose chemi- cal structure is identical except for the length of an alkyl ester pendent chain present at each mo- Correspondence to: J. Kohn nomeric repeat unit. By using the ethyl, butyl, Contract grant sponsor: Consejo Nacional de Investigaciones hexyl, or octyl esters, the length of the pendent Cientificas y Tecnolo ´gicas (CONICIT), Caracas, Venezuela Contract grant sponsor: Programa de Nuevas Tecnologı ´as chains was varied in steps of two methylene Contract grant number: NM-012 groups from two to eight carbons (Fig. 1). The Contract grant sponsor: National Institutes of Health availability of such a series of structurally related Contract grant number: GM39455  1997 John Wiley & Sons, Inc. CCC 0021-8995/97 / 111457-10 polymers facilitated the identification of struc- 1457 / 8E70$$RUT8 01-10-97 10:29:44 polaa W: Poly Applied