THERMAL-PROPERTIES AND ENTHALPY RELAXATION OF TYROSINE-DERIVED POLYARYLATES

Sixteen degradable, tyrosine-derived polyarylates with well-defined ch emical structures were used to study the effect of polymer structure o n the glass transition temperature and enthalpy relaxation kinetics (p hysical aging). These polyarylates compose a model system where the nu mber of methylene groups present in either the pendent chain or the po lymer backbone can be altered independently and in a systematic fashio n. Quantitative differential scanning calorimetry was employed to meas ure the glass transition temperature and the enthalpy relaxation kinet ics. Correlations between these material properties and the polymer st ructure were established. The glass transition temperature of this fam ily of polymers ranged from 13 to 78 degrees C. The addition of methyl ene groups to either the pendent chain or the polymer backbone made a fairly constant contribution to lowering the glass transition temperat ure. The rate of enthalpy relaxation increased with an increasing numb er of methylene groups in the polymer backbone, but was independent of the number of methylene groups in the pendent chain. This observation indicated that the rate of enthalpy relaxation in these polymers was limited by the mobility of the polymer backbone. The enthalpy relaxati on data was fitted to the Cowie-Ferguson model and the relaxation time s obtained ranged from 44 min to about 100 min. Although these structu re-property correlations facilitate the design of new materials with p redictable thermal properties, they are rarely investigated for biomed ical polymers. (C) 1997 John Wiley & Sons, Inc.