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 dianhyd ride (BPDA) and either 1,3-bis(4-aminophenoxy)benzene (134APB) or 1,12 -dodecanediamine (C12), as well as copolyimides containing different c ompositions of 134APB and C12. For copolyimides, although a singular g lass transition was seen in each composition, the crystallization and melting behavior of all compositions is dominated by either 134APB/BPD A or C12/BPDA homopolyimide crystals. The bulk crystallization rate is significantly reduced in compositions with high C12 content. Composit ions of copolyimides with 40/60 and 20/80 134APB/C12 ratios additional ly exhibited dual maxima in crystallization rates which can be attribu ted to the phase separation of the two crystals. Since no large depres sion in the spherulite growth rate was found, the decrease in the bulk crystallization rate is primarily due to the decrease in nucleation d ensity. The last endotherm in the triple-melting behavior is associate d with a reorganization process rather than the polymorphism, as verif ied by DSC and X-ray diffraction. Finally, two major spherulite appear ances were identified: (1) Maltese-cross spherulites with negative bir efringence in 134APB/BPDA dominant systems; (2) ringed-like spherulite s with no preferred birefringence in C12/BPDA dominant systems. Both m orphologies 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.