A new polyimide was synthesized from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 2,2-dimethyl-l,3-(4-aminophenoxy)propane (DMDA), and abbreviated to be BTDA-DMDA. This polymer possesses three relaxation processes which have been observed through dynamic mechanical and dielectric analyses above -150°C. The a relaxation process has been assigned to be the glass transition and occurs at about 250 "C with an apparent activation energy of 420 kJ/mol. Two subglass relaxation processes are aprelaxation process at around 100-170 "C in a frequency range from 0,l Hz to 100 kHz with an activation energy of 182 kJ/mol and a y relaxation process occurs at around -80 "C with an activation energy of 44 kJ/mol. Carbon-13 solid state nuclear magnetic resonance experiments were carried out for the study of molecular dynamics at different temperatures. The results indicate that the y relaxation is responsible for an oscillation and R flipping motion of the two phenoxy rings in the DMDA portion. Theprelaxation was shown to pertain to the kHz-motion of the aromatic imide rings in the BTDA portion. The molecular motion of the DMDA and BTDA portions are largely decoupled from each other in the frequency region studied.

A new semicrystalline polyimide has been synthesized from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride and 2,2‐dimethyl‐1,3‐(4‐aminophenoxy)propane. The polymer has a high glass transition temperature of 230°C and a melting temperature of 325°C. Its overall crystallization rate between 240 and 325°C is quite fast (t1/2<10min) and relatively insensitive to the crystallization temperature. Although the degree of crystallinity obtained is dependent on the crystallization conditions, it can be as high as 50%. The polymer's morphology, which was examined with transmission electron microscopy (TEM), has a randomly stacked, ribbon‐like, lamellar texture. Both TEM and polarized light microscopy show that mature spherulites do not develop. The crystal unit cell, which was determined from wide‐angle X‐ray diffraction measurements on highly oriented films, is monoclinic with a = 0.960nm, b = 0.582nm, c = 2.46nm and γ = 81.1°.

Thermal properties of a new semicrystalline polyimide synthesized from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and 2,2‐dimethyl‐1,3‐(4‐aminophenoxy)propane (DMDA) have been studied. Heat capacities in the solid and liquid states of BTDA‐DMDA have been measured. The heat capacity increase at the glass transition temperature (Tg = 230°C) is 145 J/°Cmol for amorphous BTDA‐DMDA. The equilibrium heat of fusion of the BTDA‐DMDA crystals has been obtained using wide‐angle X‐ray diffraction and differential scanning calorimetry measurements, and is 75.8 kj/mol. Based on the information on crystallinity and the heat capacity increase at Tg, a rigid amorphous fraction is identified in semicrystalline BTDA‐DMDA samples, which represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample, which should be associated with crystal sizes, and therefore with crystal morphology. It has also been found that this polymer has a high‐temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies of BTDA‐DMDA in nitrogen and air are determined to be 154 and 150kJ/mol, respectively.

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