Effect of solvent character on polymer entanglements

Abstract

In the recent paper we discussed the influence of solvent on the magnitude of the low-shear limiting viscosity ratio η_r = η₀/ η_a for polymer solutions over a wide range of concentrations. The data presented there demonstrated that thermodynamically poor solvents led to much higher viscosities at high concentrations than did good solvents. This behavior is opposite to low-concentration results, where poor solvents lead to lower viscosities because of eoil shrinkage. The traditional picture of melts and polymer solutions at high concentration attributes their generally high viscosities to the existence of entanglement networks. This concept was invoked to explain the above solvent effects. In poor solvents, the entangled chains cling together more tightly and perhaps form multimolecular aggregates before entanglements occur in the classical sense. Our objective here is to compare the onset of such phenomena with the predictions of previous theory and correlation. It is found that solvent effects, previously neglected, can lead to significant errors in such estimates.