Dependence of intrinsic viscosity and molecular size on molecular weight of partially hydrolyzed polyacrylamide

As a typical water-soluble polymer, ultra-high molecular weight (UHMW) partially hydrolyzed polyacrylamide (HPAM) has been widely used in various industries as thickeners or rheology modifiers. However, precise determination of its critical physical parameters such as molecular weight, radius of gyration (R-g) and hydrodynamic radius (R-h) were less documented due to their high viscosity in aqueous solution. In this work, the molecular structure of five UHMW-HPAM samples with different MW was elucidated by H-1 and C-13 NMR spectroscopy, and their solution properties were characterized by both static and dynamic light scattering. It is found that all the second virial coefficient (A(2)) values are positive and approaching zero, indicating of a good solvent of 0.5 M NaCl for UHMW-HPAM. The weight-average molecular weight (M-w) dependence of molecular size and intrinsic viscosity [eta] for these series of HPAM polymers with MW ranging from 4.81 to 15.4 x 10(6) g center dot mol(-1) can be correlated as R-g = 3.52 x 10(-2)M(w)(0.51), R-h = 1.97 x 10(-2)M(w)(0.51), and [eta] = 6.98 x 10(-4) M-w(0.91), respectively. These results are helpful in understanding the relationship between molecular weight and coil size of HPAM polymers in solution, and offer references for quick estimation of molecular weight and screening of commercial UHMW-HPAM polymers for specific end-users.

Automated summary

In this study, the molecular structure and solution properties of different molecular weight ultra-high molecular weight HPAM samples were investigated using NMR spectroscopy and light scattering techniques. The results showed a correlation between molecular size, intrinsic viscosity, and molecular weight of HPAM polymers, providing insights into the relationship between molecular weight and coil size in solution. These findings can serve as a reference for estimating molecular weight and selecting commercial UHMW-HPAM polymers for specific end-users.