Linear versus nonlinear determinations of equilibrium melting temperatures of poly(trimethylene terephthalate) and miscible blend with poly(ether imide) exhibiting multiple melting peaks

摘要

Multiple melting peaks in some semicrystalline polymers such as poly(trimethylene terephthalate) (PTT) have caused some difficulty in estimating accurately the equilibrium melting points. PTT forms a miscible blend with amorphous poly(ether imide) (PEI); for comparison purposes, a miscible system of a fixed composition (PTT/PEI of weight ratio=9/1) was determined. PTT and its miscible blend both exhibited dual melting peaks (labeled as low and high peaks: T-m,T-L, T-m,T-H), and the first peaks (T-m,T-L), not the second peak (T-m,T-H), should be used for extrapolation. The equilibrium melting temperatures (T-m(0)) of neat PTT and its blend PTT/PEI (9/1) were 245.2 and 242.4inverted perpendicularC, respectively, by the linear Hoffman-Weeks treatment using the corrected values of T-m,T-L (i.e., values obtained using a heating rate close to zero). Linear and nonlinear treatments led to a significant difference in estimated T-m(0), and the relative validity of these two methods is discussed. The nonlinear estimate yielded a higher value by about 27.3degreesC for neat PTT and 23.1degreesC for the PTT/PEI (9/1) blend, respectively (also the correction in T-m,T-L at the same condition mentioned previously). Results showed melting depression in miscible PTT/PEI (9/1). In addition, the T-m(0) value of neat PTT was higher than that of PTT/PEI (9/1) owing to much thicker and more-perfect crystals in neat PTT. (C) 2002 Wiley Periodicals, Inc. [References: 37]