Applications

Triple Detection GPC of Polyquaternium

Introduction

Usage: Polyquaternium is the commonly used name for several types of polycationic polymers, all of which have quaternary ammonium centers present in the polymer. These polymers are distinguished by the number that follows “Polyquaternium”, which represents their registration each as a chemically different type of polymer, e.g. Polyquaternium-1 (Polyquad). The quaternary ammonium salt, polyquaternium-1 is classified as a cationic surfactant with excellent antibacterial and preservative characteristics. Due to the positive charges on these polymers, they have the ability to bind to negatively charged surfaces. This gives them a wide variety of applications such as: stripping agent in water treatment, conditioning agent in hair and skin care products, and antistatic and softening agent in leather and fibers. Polyquad was initially developed for use in multipurpose care solutions of contact lenses as a high molecular weight biocide that attacks pathogens by binding to the negatively charged phospholipids located in the bacterial cell membrane, resulting in cellular lysis. Gel permeation chromatography (GPC) with triple detection, employing a light scattering detector and viscometer, may be used to determine accurate molecular weights and molecular weight distribution for polyquad polymers. This information is used to assess their physical properties, such as solubility, as well as pharmacokinetic properties to ensure optimum performance.

Manufacturing: There are many different types of these polymers, which are differentiated by their structure, molecular weight and size, and charge density. Some of these are derived by the modification of cellulose, guar gum, starches, polypeptides and proteins from various animal and plant sources, while others are completely synthetic.

Chemical Formula: C22H48Cl3N3O6 Chemical Structure

Molecular Structure of Polyquaternium-1

Figure 1. Molecular structure of Polyquaternium-1

Instrumentation

Two polyguanidine samples were dissolved in 5% Acetic acid at a concentration of 5 mg/mL and left to dissolve overnight while shaking before filtering through 0.22µm nylon filters. Analysis was completed on a Viscotek Triple Detector Array (TDA) 302 equipped with a Refractive Index (RI) detector, Viscometer, Right Angle (90o) Light Scattering (RALS) and Low Angle (7o) Light Scattering (LALS). Separation was performed using two C-MBHMW-3078 columns for cationic polymers (Viscotek) connected in series. These columns were used to overcome any potential interaction of the cationic polymer with the column packing of non-charged column packing since GPC must operate free of interactions to assure separation by size only. Samples were injected at a volume of 100 µL and eluted through the system at flow rate of 1 mL/min 5% acetic acid. A temperature of 30oC was maintained during separation and detection.

Results and Discussion

Figure 2 is an overlay of the molecular weight distributions of two polyquaternium sample which displayed similar molecular weights with only slight differences across the distributions.

Overlay Plot of the Reflective Index Response Versus Retention Volume of Polyquaternium

Figure 2. An overlay plot of the RI chromatograms of two polyquaternium samples

Figure 3 shows an overlaid multi-detector chromatogram for a sample of polyquaternium-1 which delivered strong signals in the detectors. The molecular weight values of the polyquad samples reported in Table 1 were determined by the Right Angle (90o) Light Scattering detector.

Overlay Plot of the Detector Response Versus Retention Volume of Chromatograms for Polyquaternium

Figure 3. A typical multi detector overlay of chromatograms for a sample of polyquaternium.

Table 1. Molecular weight parameters and size data derived from triple detection using Omni-Sec software.

Table of the Molecular Weight Parameters and Size of Polyquaternium

Overlay of the Mark-Houwink Plots of Polyquaternium

Figure 4. An overlay of the Mark-Houwink plots of two polyquaternium samples

Figure 4 shows the overlaid Mark-Houwink plot of log intrinsic viscosity as a function of log molecular weight for the two samples. Both samples display a similar relationship between increasing molecular weight and increasing intrinsic viscosity, indicating that the polyquaternium samples were of a comparable structure. The difference in molecular weight observed may be attributed to differences in synthesis methods rather than changes to the nature of the polymers themselves.

Conclusion

Triple detection GPC employing a viscometer and a light scattering detector with a concentration detector was successfully used to assess the molecular weight distribution and molecular structure of the commercially important polymer, Polyquad, without having to rely on column calibrations.

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