Effect of molecular structures on polyimide properties: Comparison between estimations and experiments

Abstract The density and glass transition temperature ( T g ) of 11 polyimides were investigated by experiments and predictions using the connectivity indices method to explore the structure–property relationships. The predicted results are in good agreement with the experimental data. The mean interchain spacings ( d ‐spacings) of polyimides increase with the introduction of bridging groups, i.e., following the order: PDA < BZD < ODA < MDA < BDAF, while the densities increase in the order of MDA < BZD < PDA, and cohesive energy densities (CEDs) of polyimides change following the order of BDAF < MDA < ODA < BZD < PDA. In addition, the glass transition temperatures ( T g 's) increase as the CEDs increase for the polyimides prepared from the same dianhydride and different diamines, whereas no certain correlation exists between T g 's and the values of the characteristic ratio ( C ∞ ). This indicates that the strength of interchain interaction influences the T g 's of polyimides much stronger than the chain flexibility. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 998–1003, 2007