Affordable, UV-, heat- and water-resistant radiochromic film composed of diacetylenes having chromophoric groups

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Project Summary: Self-developing, instant radiochromic films based on the solid-state polymerization of diacetylenes (R-C≡C-C≡C- R’, where R and R’ are substituent groups) are used for measuring radiation therapy dose. Currently available radiochromic films, e.g., the GafChromicTM EBT films from Ashland (Bridgewater, NJ, USA), have many drawbacks such as they are very expensive, sensitive to water and ambient UV light, requiring cold storage and shipping, a short shelf-life, delamination of the coating if bent sharply or cut, non-uniform coating requiring a yellow dye for thickness correction, etc. These shortcomings have prevented their broader use in radiation therapy clinics. Hence, there is a strong need for more economical radiochromic films, which do not have the drawbacks of commercially available radiochromic films. One of the principal investigators, G.N. Patel, is one of the early pioneers in the field of diacetylenes and is still active in the field. His company, JP Laboratories, Inc., has developed radiation dosimeters and radiochromic films for radiation protection and other non-medical applications. Utilizing his extensive experience in diacetylene chemistry and synthesis, we will synthesize a class of diacetylenes, which have a chromophoric group as a substituent group, e.g., R = (CH2)n-OCONH-(CH2)n-A, where n=1-4, A is a light yellow color chromophoric group. The chromophoric diacetylenes (CD) will be produced by reacting diacetylene diols with chromophoric isocyanates. Then, CD-based emulsion, a coating formulation, will be prepared and uniformly coated on a polyester film substrate to create a CD film. Diacetylene diols are significantly less expensive than those used to make GafChromicTM films. The radiochromic films made from chromophoric diacetylenes, the CD film, will have none of the drawbacks of GafChromicTM films. The chromophoric group will absorb UV light. Hence the CD film will not develop color upon exposure to ambient UV light. The CD film will not require a yellow marker for the thickness correction because the CD is yellow. Diacetylenes with urethane (- OCONH-) functionality usually have a higher melting point (above 100°C), resulting in a longer shelf-life, and are not affected by water/humidity. Because of the high melting point of CD, the CD film can be briefly heated to eliminate the post-irradiation change of measured dose, allowing an instant reading of the radiation dose. In the first stage of the project, small quantities of chromophoric diacetylenes will be synthesized, inks/emulsions made of CD will be coated on a substrate to make the radiochromic films, and the prototype films will be evaluated. The best performing CD film will be selected, and a sufficient quantity of the film will be made for the extensive evaluation for radiation therapy applications. In the second stage, the chosen CD film will be assessed for the effect of dose, dose rate, energy, UV light, water/humidity, and heat (shelf-life). JP Labs and the University of Minnesota facilities are fully equipped to carry out the proposed work.