Thermal and Rheological Properties of Miscible Polyethersulfone/Polyimide Blends

Blends of an aromatic polyethersulfone (commercial name Victrex) and a polyimide (com- mercial name Matrimid 5218), the condensation product of 3,3’,4,4’-benzophenone tetra- carboxylic dianhydride and 5 (6)-amino-1- (4’-aminophenyl) -1,3,3’-trimethylindane,were studied by differential scanning calorimetry, dynamic mechanical analysis, and rheological techniques. The blends appeared to be miscible over the whole range of compositions when cast as films or precipitated from solution in a number of solvents. After annealing above the apparent phase boundary, located above Tg,the blends were irreversibly phase separated indicating that the observed phase boundary does not represent a true state of equilibrium. Only a narrow “processing window” was found for blends containing up to 20 wt % polyimide. Rheological measurements in this range of compositions indicated that blending polyether- sulfone with polyimide increases the complex viscosity and the elastic modulus of the blends. For blends containing more than 10 wt % polyimide, abrupt changes in the rheological properties were observed at temperatures above the phase boundary. These changes may be consistent with the formation of a network structure (due to phase separation and/or crosslinking) .Blends containing less than 10 wt % polyimide exhibited stable rheological properties after heating at 320°C for 20 min, indicating the existence of thermodynamic equilibrium

Heat capacity of poly(trimethylene terephthalate)

Thermal analysis of poly(trimethylene terephthalate) (PTT) has been carried out using standard differential scanning calorimetry and temperature-modulated differential scanning calorimetry. Heat capacities of the solid and liquid states of semicrystalline PTT are reported from 190 K to 570 K. The semicrystalline PTT has a glass transition temperature of about 331 K. Between 460 K and 480 K, PTT shows an exothermic ordering. The melting endotherm occurs between 480 K and 505 K with an onset temperature of 489.15 K (216 C). The heat of fusion of typical semicrystalline samples is 13.8 kJ/mol. For 100% crystalline PTT the heat of fusion is estimated to be 28--30 kJ/mol. The heat capacity of solid PTT is linked to an approximate group vibrational spectrum, and the Tarasov equation is used to estimate the skeletal vibrational heat capacity ({Theta}{sub 1} = 542 K and {Theta}{sub 3} = 42 K). A comparison of calculation and experimental heat capacities show agreement of better than {+-}2% between 190--300 K. The experimental heat capacity of liquid PTT can be expressed as a linear function of temperature: C{sub p} {sup L}(exp) = 211.6 + 0.434 T J/(K mol) and compares well with estimations from the ATHAS data bank using group contributions of other polymers with the same constituent groups ({+-} 0.5%). The change of heat capacity at T{sub g} of amorphous PTT has been estimated from the heat capacities of liquid and solid to be 86.4 J/(K mol). Knowing C{sub p} of the solid, liquid, and the transition parameters, the thermodynamic functions: enthalpy, entropy and Gibbs function were obtained

Poly(trimethylene teraphthalate) crystal structure and morphology in different length scales

Poly(trimethlene teraphthalate) (PTT) is one of the terephthalic polyester family members which can crystallize between its glass transition and melting temperatures. The crystal structure has been determined using both electron diffraction (ED) on single crystals and wide angle X-ray diffraction on powder and oriented fibers. The unit cell is triclinic with dimensions of a = 0.46 (3) nm, b = 0.61 (2) nm, c = 1.86 (1) nm, alpha = 97.5 degrees, beta = 92.1 degrees, and gamma = 110 degrees. The bulk PTT samples usually crystallize to form spherulites in the crystallization temperature (T-c) region studied. Between T-c = 135 and 165 degreesC, the spherulites show a banded texture, and the band spacing increases with increasing T-c. The radial direction in the spherulites has been determined to be the crystal a-axis. Observations of successive ED patterns taken along the radial direction of a spherulite within one band reveal twist of lamellar crystals along the spherulite radial direction. The chain-folding direction, determined using a polyethylene decoration method, is along the a-axis direction in the lamellar crystals and parallel to the radial direction in the spherulites. Linear growth rates of the spherulites have also been measured and the maximum growth temperature is located at 165 degreesC. This temperature is also the upper-limit temperature for PTT banded texture spherulite formation. (C) 2001 Elsevier Science Ltd. All rights reserved