Structural Rigidity of Aromatic Polyamides with Bulky Lateral Substitutions

In the present study the effect that controlled structural modifications have on the physical and conformational properties of a series of isomeric aromatic polyamides synthesized with different bulky pendant lateral groups was investigated. Physical properties of the aromatic polyamides such as thermal properties were determined by differential scanning calorimetry. Structural changes were determined by Fourier transform infrared spectroscopy, density and fractional free volume (FFV). Light scattering and dynamic-mechanical analysis were used to characterize the thermodynamic and kinetic rigidity. Vogel's model was applied to evaluate kinetic rigidity in polyamide chains and the results were compared with physical properties data. It was found that there was a relationship between T-g and the conformational entropy determined by the structure which indicates that the higher the level of rigidity in the polyamide the higher the value of T-g. For kinetic rigidity, it was found that the relaxation time at infinite temperature B-a, was very close to the value 5 x 10(-12) s, reported for other amorphous glassy materials. There was also a relationship between the activation energy of the glass transition U-infinity and FFV, which is determined by the presence or absence of the bulky functional groups, indicating that the smaller the FFV, the higher the energy required for the glass transition to take place.