Controlling molecular mobility and ductile-brittle transitions of polycarbonate copolymers

To control molecular mobility and study its effects on mechanical propertie s, we synthesized two series of poly(ester carbonate) and polycarbonate cop olymers with different linkages: (B(x)t)(n) (x = 3, 5, 7, 9) and (BxT)(n) ( x: = 1, 3, 5, 7, 9), where t represents the terephthalate, T represents the tetramethyl bisphenol A carbonate linkages, and B is the conventional bisp henol-A (BPA) carbonate. These two series of materials have distinct differ ences in their relaxation behaviors and chain mobility, as indicated by the pi -flip motion of the phenylene rings in the B-x blocks. Uniaxial tensile tests of the copolymers indicate that the brittle-ductile transition (BDT) temperatures of the copolymers are correlated to whether the gamma -relaxa tion peaks due to the B-x sequence is fully established. The materials poss essing more fully established low-temperature gamma peaks give rise to a lo wer BDT. Also, the locations of the gamma peaks are correlated to the ring flips of the B-x blocks of polymer chains. (C) 2001 John Wiley & Sons, Inc.