Light scattering from reacting polymer systems. Associating polymers in a good solvent

The forward scattering of light allows determination of the osmotic modulus (=inverse osmotic compressibility), which in good solvents is a measure of repulsive forces among the particles in solution but also depends on the molar mass of the particle. The osmotic modulus increases with concentration if the particle weight remains constant. The increase differs for particles of different architecture and can for c < 3c* be described by structure specific g‐factors, where g is defined through A3=gA22 Mw with A2 and A3 being the 2nd and 3rd virial coefficients. For associating systems in a good solvent also the particle weight increases with c. A procedure is suggested which allows within limits a correction of the measured apparent molar mass M̄app (c) for the true molar mass M̄w (c) at the concentration c. Three examples are discussed in detail.