INVESTIGATIONS OF THE PRACTICAL ROUTES, STRUCTURE, AND PROPERTIES FORPOLY(ARYL ETHER KETONE KETONE) POLYMERS

Different routes for preparing poly(aryl ether ketone)s (PEKKs) are pr esented and compared. The properties of PEKKs are related to the conte nt of metaphenyl links in the molecular main chains, the molecular cha in branching degree, the gelation content by molecular crosslinks, and , especially, the relative content of crystal form II to crystal form I of the PEKK polymorphism. When the molecular T/I ratio of 50/50 in t he polymer chains is reached, the obtained PEKK has a lower melting po int and gelation content (2% or so). The PEKKs prepared from the elect ronical substitution route (E route) often have a 0-30% content of cry stal form II (relative to the mixed form I and form II), which is much more than that in PEKKs from the nucleophilic substitution route (N r oute, form II accounts for 0-20%). The relatively unstable crystal for m II resulted in the unstable and difficultly predicted thermal proper ties of PEKKs. PEKKs from different routes provide samples with meltin g points from 360 to 397 degrees C (T-m) and glassy transition tempera tures (T-g) from 167 to 176 degrees C and the equilibrium melting poin t of 411 degrees C for para-PEKK, while the tensile strength of the ho mopolymer PEKK and copolymers of PEEKK (poly(aryl ether ether ketone k etone)-PEKK can reach 100 MPa prepared by the N route. The high T-g ma kes PEKK polymers practically useful while too high T-m and a very sma ll difference between T-m and T-d (degradation temperature) produce ob stacles to its wide application. The reaction mechanisms of both elect rophilic and nucleophilic routes are investigated and discussed in det ail. Results show that the molecular chain branched by solvents and mo nomers with many activated points may be partly reduced to some extent by the oligomer and extruding route. (C) 1998 John Wiley & Sons, Inc.