Azidation of polyesters having pendent functionalities by using NaN ₃ or DPPA-DBU and photo-crosslinking of the azidopolyesters

In this article, we performed dehydration polycondensation of bromosuccinic acid and methylsuccinic acid with 1,4-butanediol at 80°C to synthesize aliphatic polyesters containing pendent bromo groups without dehydrobromination using scandium trifluoromethanesulfonate (Sc(OTf)₃) as the catalyst. Azidation of the resultant polyesters was carried out readily in N,N-dimethylformamide at room temperature using sodium azide (M_n = 8.3 × 10³ (M_w/M_n = 2.17)). ¹H nuclear magnetic resonance analysis of the product revealed that 65% contained azide functionality, and dehydrobromination occurred in 35% during the azidation process. On the other hand, azidation of poly(butylene bromoadipate-co-butylene methylsuccinate) (poly(BBA-co-BMS)) proceeded successfully under the same conditions to generate poly(butylene azidoadipate-co-butylene methylsuccinate) (poly(BAA-co-BMS)) without dehydrobromination (M_n = 10.4 × 10³ (M_w/M_n = 2.71)). We successfully photo-crosslinked the resultant azidopolyester by ultraviolet irradiation and examined it using scanning electron microscope. We also described azidation of polyesters having pendent hydroxyl groups by using the DPPA (diphenylphosphoryl azide)-DBU (1,8-diazabicyclo5.4.0undec-7-ene) substitution strategy to produce water-soluble polyesters containing pendent azido groups (M_n = 7.5 × 10³ (M_w/M_n = 2.25)). These azidopolyesters might be extremely useful not only for their derivatization by simple chemical modification but also for their effective utilization as photolithography material.