Sixteen degradable, tyrosine-derived polyarylates with well-defined chemical structures were used to study the effect of polymer structure on the glass transition temperature and enthalpy relaxation kinetics (physical aging). These polyarylates compose a model system where the number of methylene groups present in either the pendent chain or the polymer backbone can be altered independently and in a systematic fashion. Quantitative differential scanning calorimetry was employed to measure the glass transition temperature and the enthalpy relaxation kinetics. Correlations between these material properties and the polymer structure were established. The glass transition temperature of this family of polymers ranged from 13 to 78ЊC. The addition of methylene groups to either the pendent chain or the polymer backbone made a fairly constant contribution to lowering the glass transition temperature. The rate of enthalpy relaxation increased with an increasing number 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 relaxation data was fitted to the Cowie-Ferguson model and the relaxation times obtained ranged from 44 min to about 100 min. Although these structure-property correlations facilitate the design of new materials with predictable thermal properties, they are rarely investigated for biomedical polymers.
Liquid crystal polyurethane (LCPBI) containing biphenylnate and imide units was synthesized and characterized and used to modify the conventional epoxy resin (E-51). Experimental results revealed that the impact strength of the epoxy resin modified with LCPBI was 2.5 times higher than that of unmodified epoxy resin, and the tensile strength as well as the bending strength was also improved. The thermal decomposition temperature of modified systems was also 15-20oC higher than that of the unmodified system, and the fracture structures of the blends was investigated by SEM.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.