Enhancement of the crystallinity of a thermoplastic polyimide

The polyimide based on 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 1,4-diaminobutane (poly(BTDA-DAB)) does not crystallize from the melt. This paper describes attempts to enhance the crystallization of this polyimide. The spherulitic growth rate and the nucleation density of pure poly(BTDA-DAB) (M¯w = 35 300) are quite low, namely G = 0.031 μm min-1 and 1.7 × 107 cm-3 respectively, both at 240°C. Classical nucleating agents, such as talc and non-coated glass fibre, raise the nucleation density to 6-7 × 109 cm-3 but endcapping the polyimide chains with -φ-SO3Na endgroups results in a nucleation density of 3.3 × 1015 cm-3. The highest crystallization rate is obtained for a sample in which 4.7% of the chains have been endcapped with -φ-SO3Na. Upon cooling from the melt at 20°C min-1, the heat of crystallization of this sample is ca. 32J g-1, corresponding to a crystallinity of ca. 35%. Further, this paper demonstrates the synergistic effect of the simultaneous presence of -φ-SO3Na endgroups and 10 wt% of 4-hydroxybenzophenone as plasticizer. Further optimization is necessary to obtain a high molecular weight, semicrystalline poly(BTDA-DAB) upon injection moulding.