The Specific Refractive Index Increment and the Partial Specific Volume of Atactic Poly (2-vinylpyridine)

Abstract The specific refractive index increment, dn⁄dc, of atactic poly(2-vinylpyridine) was measured in 18 solvents with 436 nm light at 25 °C. Using these data, the partial specific volume, \barν2, of the polymer in these solvents was then evaluated by means of the method proposed by Heller. A sufficient agreement was found between the values of \barν2 thus obtained optically and those determined directly by the density measurement of solutions in several solvents. It was found that \barν2 varies considerably with the kind of solvent and that, in some solvents, such as methanol and ethanol, it takes an extremely lower value than that of bulk crystalline isotactic poly(2-vinylpyridine). The results were discussed in terms of thermodynamic interactions between the polymer and the solvent, the molar volume, and the compressibility of the solvent molecule. The relationship between dn⁄dc and the refractive index of a solvent, n1 for 436 nm light is expressed by dn⁄dc=0.900× (1.628–n1).