What is the refractive index of poly(methacrylamide)? I've been looking for the index of refraction for poly(methacrylamide). I searched several vendors and in https://polymerdatabase.com/ with no success. Is there any database where I can find this information?

The refraction index of the monomer would be useful too.
As reported in  Gooch JW (Jan W. Encyclopedic Dictionary of Polymers. Springer; 2011. doi:10.1007/978-1-4419-6247-8. Poly(N-methyl methacrylamide) has a refractive index of 1.5398