A novel approach using differential scanning calorimetry to investigate the dissolved state in aqueous solutions of polymers used for papermaking

Abstract The size and conformations of dissolved polymer molecules of polyethylene glycol (PEG) in 5% aqueous solutions were examined through the use of differential scanning calorimetry (DSC). As long as the freezable bound water is considered to be the water enclosed by the entangled polymer chains in the solution, the appearance of the characteristics of a polymer begins to occur at a degree of polymerization (DP) between 11 and 21 and is largely completed at a DP of about 50. Assuming that the peak temperature of the DSC curve for the freezable bound water indicates the size of the entangled molecular coil, the lowering of the peak temperature with a decrease of molecular weight (MW) suggests a decrease in the size of the entangled molecular coil. The linear relationship between the peak temperature and the reciprocal of the number‐average MW suggests melting point depression as a plausible mechanism for the peak temperature lowering. Mixing of two polymers with different MWs—and thus, entangled molecular coils of different sizes—causes a kind of polymer–polymer interaction and the coil sizes change as follows. If the difference in the values of the two MWs is large, the sizes of the entangled molecular coil of each MW are brought closer to each other. The extent of approach is roughly proportional to the mixing ratio. If the difference in the values of the two MWs is not large, the original entangled molecular coils disappear and a single molecular coil of intermediate size appears instead. The size of the single intermediate molecular coil varies roughly according to the simple mixing law for the values of the two MWs. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2798–2807, 2003