Theoretical and Experimental Study of Thymine Based Photoresist Polymers

J. VICH, N. CASÍS, C. LUCIANI, D. MARTINO, D. ESTENOZ, J. WARNER

Washington, EEUU.

Congreso; Green Chemistry; 2007

Green Chemistry

Styrene-based biopolymers containing ionic and thymine groups chemically attached to the polystyrene structure were experimental- and theoretically investigated. The ionic groups make the polymer water-soluble, eliminating the environmental and health concerns associated with the use of volatile organic solvents as in conventional photoresist processes. Also, when the biopolymers are illuminated with UV light, a photocyclization reaction between adjacent thymines takes place, rendering it water-insoluble. The material obtained is called a photoresist. Vinylbenzyl thymine (VBT) was copolymerized in a batch solution process with vinylbenzyl triethylammonium chloride (TEQ) or vinylphenylsulfonic acid sodium salt (SSA). The reactions were carried out at 65 C in a batch-stirred tank reactor using 2,2’-azobisisobutyronitrile (AIBN) as initiator. Samples were taken along the reactions to determine monomer conversion, solubility, chemical composition, and molecular weight distribution. The obtained copolymers were cured by UV irradiation at room temperature. The addition of sensitizer molecules to irradiate at wavelengths in the visible range (520nm) and the effects of irradiation dose and the molecular structure and chemical composition of the polymer on the curing process were investigated. The cured material was characterized by AFM, FTIR, and UV-Vis Spectroscopy. A mathematical model that simulates the synthesis of the biocompatible polymers was developed. The model enables the calculation of the evolution of the reagent and product concentrations and the molecular weight distribution of the copolymer. Theoretical predictions are in good agreement with measurements. Also, for the curing process, a recursive statistical model was presented to compute the evolution of the weight average molecular weight before gelification, the gel point, and the evolution of the weight fraction of soluble material after gelification.