Laser Light Scattering Studies of Soluble High-Performance Polyimides:  Solution Properties and Molar Mass Distributions

Two soluble high-performance polyimides, poly(BCPOBDA/DMMDA) and poly(ODPA/DMMDA), in CHCl 3 at 25 °C have been studied using laser light scattering. We found that the z -average radius of gyration (〈 R g 〉) can be scaled to the weight-average molecular weight ( M w ) as 〈 R g 〉 (nm) = 4.95 × 10 -2 M w 0.52 and 〈 R g 〉 (nm) = 1.25 × 10 -2 M w 0.66 respectively for poly(BCPOBDA/DMMDA) and poly(ODPA/DMMDA), indicating that poly(ODPA/DMMDA) in CHCl 3 at 25 °C has a more extended chain conformation than poly(BCPOBDA/DMMDA). Using the wormlike chain model approach, we found that the Flory characteristic ratios ( C ∞ ) of poly(BCPOBDA/DMMDA) and poly(ODPA/DMMDA) are ∼20 and ∼31, respectively, indicating that both of them have a slightly extended chain conformation in comparison with typical flexible polymer chains, such as polystyrene, whose C ∞ is ∼10. A combination of the weight-average molar mass ( M w ) with the translational diffusion coefficient distributions ( G ( D )) has led to D (cm 2 /s) = 3.53 × 10 -4 M -0.579 and D (cm 2 /s) = 4.30 × 10 -4 M -0.613 respectively for two soluble high-performance polyimides, poly(BCPOBDA/DMMDA) and poly(ODPA/DMMDA), in CHCl 3 at 25 °C. Using these two calibrations, we have successfully characterized the molar mass distributions of the two polyimides from their corresponding G ( D )s. The exponents of these two calibrations further confirm that both of the polyimides have a slightly extended coil chain conformation in CHCl 3 . The chain flexibility difference between these two polyimides has also been discussed.