It was observed that the poly(3,5-dimethylphenyl acrylated) is soluble in the mixture of triethylamine and acetonitrile but not in any of them alone. Therefore, the densities of twenty (20) binary mixtures of acetonitrile and triethyamines from 10°C to 46°C were measured by an Anton Paar DMA 5000 model density-meter. The partial specific volume were estimated by adjusting the best curve fitted to the data and the intercepts of the line tangent to the curve at a given composition and temperature using Microsoft Excel. The thermal expansion of the binary mixture along with partioal specific volume was tabulated and was related to the physicochemical property of the mixture. These data will be use to study the physical-chemical properties of the newly synthesized poly(3,5-dimethylphenyl acrylate) in the binary solution.