Crystalline homopolyimides and copolyimides derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride/1,3-bis(4-aminophenoxy)benzene/1,12-dodecanediamine. 2. Crystallization, melting, and morphology

A study of crystallization, melting, and morphology is carried out for homopolyimides derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and either 1,3-bis(4-aminophenoxy)benzene (134APB) or 1,12-dodecanediamine (C12), as well as copolyimides containing different compositions of 134APB and C12. For copolyimides, although a singular glass transition was seen in each composition, the crystallization and melting behavior of all compositions is dominated by either 134APB/BPDA or C12/BPDA homopolyimide crystals. The bulk crystallization rate is significantly reduced in compositions with high C12 content. Compositions of copolyimides with 40/60 and 20/80 134APB/C12 ratios additionally exhibited dual maxima in crystallization rates which can be attributed to the phase separation of the two crystals. Since no large depression in the spherulite growth rate was found, the decrease in the bulk crystallization rate is primarily due to the decrease in nucleation density. The last endotherm in the triple-melting behavior is associated with a reorganization process rather than the polymorphism, as verified by DSC and X-ray diffraction. Finally, two major spherulite appearances were identified: (1) Maltese-cross spherulites with negative birefringence in 134APB/BPDA dominant systems; (2) ringed-like spherulites with no preferred birefringence in C12/BPDA dominant systems. Both morphologies consist of lamellar crystals with the 134APB/BPDA crystals having a broader thickness than C12/BPDA, as was determined by small angle X-ray scattering.