CRYSTAL MORPHOLOGY AND PHASE IDENTIFICATION IN POLY(ARYL ETHER KETONE)S AND THEIR COPOLYMERS .3. POLYMORPHISM IN A POLYMER CONTAINING ALTERNATED TEREPHTHALIC ACID AND ISOPHTHALIC ACID ISOMERS

Crystal structures and morphology of a polymer containing alternated t erephthalic acid (T) and isophthalic acid (I) Linked phenylene units i n poly(ether ketone ketone) [PEKK(T/I)] have been investigated via tra nsmission electron microscopy (TEM), electron diffraction (ED), wide a ngle X-ray diffraction (WAXD), and differential scanning calorimetry ( DSC) experiments. When the polymer is crystallized at high temperature s (at and above 310 degrees C), only one orthorhombic crystal unit cel l (form I) is found, and the crystal dimensions are a = 0.778 nm, b = 0.610 nm, and c = 3.113 nm, At the crystallization temperature below 2 00 degrees C, another orthorhombic crystal unit cell(form II) forms, h aving the dimensions of a = 0.417 nm, b = 1.108 nm, and c = 3.113 nm. Even at this low-temperature range, form II always coexists with form I except in the case of solvent-induced crystallization. A possibility of the existence of a new form (form III) is identified in a temperat ure range between 200 and 300 degrees C, and usually coexists with for m I. This form also possesses an orthorhombic unit cell with dimension s of a = 0.641 nm, b = 0.610 nm, and c = 3.504 nn. Transformations fro m form II to both forms I and III require melting and recrystallizatio n. Relatively regular-shaped lamellar crystals in PEKK(T/I) can be obs erved.