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-infinity). This indicates that the strength of interchain interaction influences the Tg's of polyimides much stronger than the chain flexibility. (c) 2006 Wiley Periodicals, Inc.