Theoretical and Experimental Study of Thymine Based Photoresists Polymers

F. GARCÍA; C LUCIANI; D. REYNA; D. MARTINO; D. A. ESTENOZ; G. MEIRA; J.C. WARNER

Foz do Iguazu

Congreso; CBECIMAT, 17° Congresso Brasileiro de Engenharia e Ciência dos Materiais; 2006

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, thereby eliminating the environmental and health concerns associated with the use of volatile organic solvents that is required in conventional photoresist processes. The material is called a photoresist, given that after illumination with UV light a photocyclization reaction between adjacent thymines takes place (crosslinking), rendering it water-insoluble. The synthesis conditions determine the molecular weights distribution and chemical composition of the copolymers, influencing the solubility and the photoreactive behavior. The curing process determines the final thermal and mechanical properties of the photoresist. The relationships between the synthesis conditions, the curing conditions, and the final mechanical and thermal properties are a challenging issue that is at present only beginning to be understood. In this work, the syntheses of water-soluble copolymers based on vinylbenzylthymine (VBT) and ionically charged monomers (vinylbenzyl triethylammonium chloride and vinylphenylsulfonic acid sodium salt) are investigated. The study focused on the effects of the monomer type, comonomer molar ratio, monomer-to-solvent ratio, reaction temperature, and reaction time, on the molecular structure, solubility, and photoreactivity properties. Samples were taken along the reactions to determine: a) monomer conversion and solubility by gravimetric analysis, and b) molecular weight distribution (MWD) by size exclusion chromatography (SEC). The obtained copolymers were cast onto a compatible substrate (polyethylene terephthalate), and cured by UV irradiation at room temperature. The cured material was characterized by Atomic Force Microscopy (AFM), Fourier Transform Infrared (FTIR), and UV-Vis Spectroscopy. A mathematical model was developed that simulates the synthesis of these biocompatible polymers. The model assumes the standard low temperature styrene kinetics, and calculates monomer conversion, copolymer composition, and MWD. It was validated with experimental data. The theoretical predictions are in good agreement with measurements.