EFFECT OF THERMAL ANNEALING AND SUPERCRITICAL FLUIDS ON THE CRYSTALLIZATION BEHAVIOR OF METHYL-SUBSTITUTED POLY(ARYL ETHER ETHER KETONE)

The glass transition temperature of MePEEK, a monosubstituted methyl d erivative of poly(aryl ether ether ketone), PEEK, is 145-degrees-C, th e same as that of PEEK. However, the onset of melting of MePEEK, cryst allized by thermal annealing, occurs at 210-degrees-C, much lower than the onset at 335-degrees-C observed for PEEK. MePEEK, crystallized by successively annealing for 100 min each at 175, 190, and 200-degrees- C, melts in a two-step process spread over a broad temperature range o f about 50 deg. This double melting behavior is observed in PEEK also. When MePEEK is annealed in a similar manner in the presence of superc ritical CO2 at 100 atm, the melting event is still broad but the two p eaks are now overlapped. Similar conditioning in the presence of super critical 0.9CO2 + 0.1CH2Cl2, and 0.9CO2 + 0.1CH3OH at 100 atm gives a single and sharp melting peak with onset at 229 and 260-degrees-C, res pectively. The melting event is now spread over about 15 deg only. The density of amorphous MePEEK is 1.233 g cm-3. The density and heat of melting of 100% crystalline MePEEK are estimated to be 1.348 g cm-3 an d 74 J g-1, respectively, on the basis of density, thermal, and X-ray diffraction measurements on semicrystalline samples. The corresponding values for PEEK are 1.40 g cm-3 and 130 J g-1.