Effects of thermal history, crystallinity, and solvent on the transitions and relaxations in poly(bisphenol‐A carbonate)

The following system of nomenclature for the transitions and relaxations in polycarbonate has been proposed: α = Tg = 150, β = 70, γ = −100, and δ = −220°C (frequency range of 10–50 Hz). The three component peaks of the γ relaxation are denoted by γ1, γ2, and γ3 relaxations correspond to phenylene, coupled phenylene‐carbonate, and carbonate motions, respectively. Dynamic mechanical analysis of poly(bisphenol‐A carbonate) using the DuPont 981–990 DMA system shows that the magnitude of the β relaxation depends upon the thermal history of the polycarbonate; annealing greatly reduces the intensity of the β relaxation. A relaxation map constructed for the β relaxation gives an activation energy of 46 kcal/mol. Exposure of polycarbonate to methylene chloride vapor for various times shows that after an induction period of about 5 min the intensity of the γ3 relaxation at −78°C decreases whereas the intensity of the γ1 relaxation of −30°C is unaffected and the ratio E″(γ1)/E″(γ3) increases linearly with the square root of time. This has been ascribed to the interaction of methylene chloride on the carbonate group in polycarbonate. Thermal crystallization of polycarbonate does not affect the positions of the γ relaxation and the glass transition peaks, but merely reduces their intensity. The glass transition peak intensity falls off sharply in comparison to the γ relaxation intensity. Both the γ3 and γ1 peaks in polycarbonate have been observed simultaneously for the first time by dynamic mechanical analysis. Impact strength measurements show that methylene chloride treatment of polycarbonate results in a change in mode of failure from ductile to brittle with a resultant 40‐fold reduction in impact energy for fracture. Thermally crystallized polycarbonate exhibits brittle fracture with very low force and energy at break.