Photoactive polyesters containing o-nitro benzyl ester functionality for photodeactivatable adhesion

The fabrication of modern microelectronic silicon devices mechanically challenges these thin silicon substrates during manufacturing operations. Melt and solution polyesterification enabled the synthesis of polyesters containing photoreactive o-nitro benzyl ester units for use as a potential photocleavable adhesive. Melt transesterification provided a solvent-free method for synthesis of 2-nitro-p-xylylene glycol (NXG)-containing polyesters of controlled molecular weights. ¹H NMR spectroscopy confirmed the chemical composition of the photoactive polyesters. Size exclusion chromatography (SEC) determined the number-average molecular weights (Mn) of the polyesters synthesized in the range of 6000 to 12000 g/mol. ¹H NMR spectroscopy confirmed increasing levels of photocleavage of the o-nitro benzyl ester functionality with increasing exposure to broad wavelength UV irradiation, and exposure levels ranged from 0-187 J/cm² UVA. Photocleaveage of approximately 90% of the o-nitro benzyl ester (ONB) units within the backbone of the polymer occurred at maximum dosage. Wedge fracture testing revealed approximately a two-fold decrease in fracture energy upon UV irradiation, suggesting that these structural adhesives offer potential for commercial "flip bonding" applications.