Estimation of the Mark-Houwink-Sakurada Parameters for the Characterization of the Molecular Weight of Peg/PEO

Poly(ethylene glycol)/Poly(ethylene oxide) are polymers extensively used in the biomedical field particularly in tissue engineering and drug delivery applications. The molecular weight (M) of the polymer is used to predict the diffusional properties of the material, the mechanical performance and other physical and chemical properties of the PEG/PEO based biomaterials. Viscometry, a well-established technique, offers a powerful tool for determining the molecular weight of polymers. Relative to other techniques such as gel permeation chromatography and light scattering, viscometric analysis is the most cost-efficient technique that can be easily adopted in most laboratories. This study utilizes the polymer-solvent relationship of the Mark-Houwink-Sakurada (M-H-S) equation, to correlate the M and the intrinsic viscosity of PEG/PEO aqueous-based solutions. To calculate the parameters of the M-H-S equation, seven M with estimated values of 3.4, 6.0, 10.0, 20.0, 150.0, 250.0, and 325.0 kDa were used at nine different concentrations ranging from 4.0 to 12.0 % w/w using water and a 5.0 % w/w NaCl aqueous solution as solvents. The molecular weight of each polymer was measured and confirmed using dynamic light scattering (DLS). Viscosity measurements for the two PEG/PEO aqueous-based systems were carried out at room temperature using an AMETEK Brookfield Viscometer. Using the intercept of the curve between the inherent/reduced viscosity and the polymer concentration for each M the intrinsic viscosity was estimated. The linearized form of the M-H-S equation, was used to calculate the parameters K and ɑ. The use of 5.0 % NaCl aqueous solution allowed us to achieve viscosity measurement for low PEG/PEO M and low values of polymer concentration. The present of the ionic environment resulted in significant changes in the values of the K and ɑ parameters of the M-H-S equation. The changes in the values of the parameters can be explained due to different polymer chain conformations in the aqueous environments given by the distinct ionic strength between the pure water and NaCl solution.