Exploration of Viable Methods to Form 1-Thia-3,4-Diazolidine-2,5-Dione (TDAD) Based Polymers

Novel, well-designed photodegradable polymers have the potential to profoundly influence society due to their wide range of applications. The photochemistry and bisfunctionality of the 1-thia-3,4-diazolidine-2,5-dione (TDAD) structure allows for the development of these unique materials. An area of particular interest with TDAD polymers is that of photoresists. Photoresists are light sensitive polymers used to coat silicon wafers that are etched to create integrated circuits, which are a vital component of modern electronics. Portions of the photoresists are photolyzed, and then a wash is required to remove the remaining organic molecules. Etching the exposed sections of the silicon wafer creates the semiconductor of the integrated circuit. If a photodegradable polymer used in this process photolyzed completely to innocuous gaseous molecules, the wash step to remove the products of the photolytic decomposition could be eliminated. The cost, waste, and time associated with this wash would therefore be unnecessary, which would have a massive impact upon the industry.

Initial experiments with TDADH utilizing base-catalyzed anion polymerization have shown that with efficient leaving groups, the intermediate TDAD anion can rearrange, leading to a thermal decomposition. Experiments using 1,2-diiodoethane have exhibited this decomposition, which is partially due to the stability of the ethylene decomposition product. New methods of forming these polymers which will avoid this rearrangement are being examined.

For instance, the method of using 1,1-disubstituated dihalides instead of 1,2-disubstituted dihalides in the anionic polymerization is being explored. Decomposition of the intermediate TDAD anion made from this type of dihalide would afford high-energy carbenes, making this undesirable thermal rearrangement unlikely.

In the latest polymerization effort diiodomethane was used in the alkylation of the TDAD salt, as it is a 1,1-dihalide that would minimize the likelihood of the undesirable rearrangement. Solubility tests indicated that solids produced by this reaction were soluble in dimethyl sulfoxide but insoluble in chloroform. Importantly, some of the solid produced is insoluble in water. The combination of insolubility in less polar organic solvents, coupled with solubility in the very polar DMSO and insolubility in water is positively indicative of the presence of a TDAD polymer or oligomer. The TDAD polymer with just a CH₂group between the rings may be so polar that it is water soluble which would explain the partial solubility the products show.

To eliminate confusion 1,1-dibromoheptane has been synthesized, which will be used to create a TDAD polymer with a long organic chain. This nonpolar group will decrease water solubility of the resulting TDAD polymer. The solubility tests would be made clearer and the carbon chain would give the polymer more groups that could be examined spectroscopically. Because TDAD polymers offer the possibility of different connecting groups a variety of syntheses are possible. Besides experimenting with alternative leaving groups and manipulating the alkylation processes as mentioned, nylon 6 approach, acid-catalysis and ring opening metathesis-type polymerizations will be explored to work towards the goal of developing a photodegradable TDAD polymer to be used in photoresists.