Crosslinking of polyimides via spirodilactone unit in polymer backbone

A new approach for the crosslinking of polyimides via the lactamization of spirodilactone unit in polyimide backbone was studied by two means: model reaction and the comparison of the properties of the polyimide precursors to those of the crosslinking polymers. Polyimides 4 and 5 were soluble in N,N′dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), N′-methylpyrrolidone (NMP), and other common organic solvents, whereas their corresponding crosslinking polymers were insoluble in these solvents. The glass transition temperatures for polyimide 5 and its crosslinking polymer were 262°C and 291°C, whereas those for polyimide 4 and its crosslinking polymer were 265°C and 360°C. The weight-loss rate of the crosslinking polymers was apparently slower than that of the precursors when the temperature was > 400°C. The 10% weight-loss temperature for the polyimides 4 and 5 was < 500°C, whereas that for the crosslinking polymers was close to or above 600°C. The results indicate that this type of crosslinking polymer has good thermal properties. The temperature for the formation of lactam was above 180°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3680–3686, 1999