Development of tetraphenylborate-based photobase generators and sacrificial polycarbonates for radiation curing and photoresist applications.

摘要

Aiming at the development of new photobase generators (PBGs) and photoimageable sacrificial materials for radiation curing and photoresist applications, this thesis research explores the potential of tetraphenylborate salts as a new class of PBGs and their uses as photocatalysts in photoinitiated base-catalyzed polymerizations, polymer cross-linking and polymer thermal degradation. The thesis work also investigates the structure-performance relationship in thermodegradable polycarbonates (PCs).;The design strategy for new PBGs involves the use of a protonated amine with tetraphenylborate as a counter ion. The photolysis of the tetraphenylborate chromophore leads to the release of free amine bases. A variety of amines can be used and converted into the corresponding PBGs. Specifically, triethylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triaza-bicycle[4.4.0]dec-5-ene (TBD) and tert-butylimino-tris(dimethylamino)phosphorane [t-BuP 1(dma)] are readily converted into the tetraphenylborate salts, which all can release the base upon irradiation below 280 nm in the solid state and in solution. The quantum yields of these PBGs are comparable to most of commercially available cationic photo-initiators. TBD·HBPh4 and t-BuP1(dma)·HBPh4 are able to release TBD and t-BuP1(dma) that are 100 and 1000 times more basic, respectively, than the strongest base ever generated among all previously reported PBGs. TBD·HBPh4 is found to be an efficient photocatalyst for the living ring-opening polymerization of cyclic esters, photo-cross-linking of polymeric materials containing the hydroxyl-ester groups, and base-amplified thermolysis of poly(propylene carbonate) (PPC). Using TBD·HBPh4 as a PBG, a dry-developing photoresist material based on PPC is successfully formulated and the positive images with a resolution better than 80 mum and an aspect ratio of 3:1 have been demonstrated.;In addition, thermodegradable PCs are functionalized to contain the photo-cross-linkable acrylate, metal-binding (e.g., amine, disulfide, pyrrolidinone and diether) and water-soluble carboxylic acid groups. The metal-binding PCs are highly labile to heat and can be completely degraded to volatile compounds at 320-380°C in an inert atmosphere. The degradation temperatures are further lowered, even close to room temperature, in the presence of acid or amine groups due to chemical amplification effect. The PCs containing pyrrolidinone or cross-linked acrylate groups can not be cleanly burned off, because their thermolysis by-products are non-volatile and become char-like ashes (> 1 wt.%). In comparison with DuPont FodelRTM silver conductor paste, the PCs-based photoimageable sacrificial paste has comparable photo-patterning ability and a lower burning temperature for image development.