Abstract
Several methods have been investigated which improve the processability of polyimide homo- or copolymer systems. In particular, the utilization of a solution imidiza tion technique in converting the poly(amic acid) intermediate to the fully cyclized polyimide has been successfully exploited. The solution imidization was conducted in N- methylpyrollidone (NMP) and an azeotroping agent, such as cyclohexylpyrollidone (CHP), at approximately 160°C for 24 hours. This technique has been shown to yield more soluble products than the corresponding bulk thermal imidization which is con ducted at higher temperatures of ∼300°C. Another important method of improving melt as well as solution processability involves the incorporation of a monofunctional reagent to obtain nonreactive end groups and controlled molecular weights. Structural modifica tion by copolymerization with more flexible oligomers such as poly(arylene ether)s may also enhance processability and possibly provide improved impact strength. In this paper, the effects of incorporating varying concentrations of poly(arylene ether) sulfone and ketone oligomers into the polyimide backbone are reported. The overall copolymer molecular weight was consistently controlled to —25,000 g/mole, with the use of small molar quantities of the monofunctional reagent phthalic anhydride. Very tough, trans parent films were obtained in all cases by compression molding copolymers at 340°C. Thermal analysis indicated that microphase separation is achievable in some cases as judged by the presence of two glass transition temperatures.