Viscosimetric study of high molecular weight polyethylene oxide

Abstract

It is well known that polyethylene oxide (PEO) type polyethers are non-ionogenic polymers and behave as electrolytically neutral in aqueous medium [1, 2]. Direct and indirect data exist, however, that PEO can specifically bond the cations of some alkaline earth and transition metals [3-6]. Since PEO is generally synthesized using a catalyst containing calcium or zinc, it may be presumed that Ca 2+ and Zn 2+ ions can be specifically bonded with the oxygen atoms of the ethylene oxide groups; consequently, the macromolecules of the polymer behave as positively charged in aqueous medium. Investigation of the IR spectra of PEO in 4.8 M CaCI2 solutions shows that Ca 2+ is really a non-indifferent ion with respect to the ethylene oxide groups [ -EO--] [7, 8]. Literature data, however, provides no direct evidence for the presence of charges directly bonded to the PEO macromolecules. The present study is a part of our investigations aimed at determining whether the macromolecules of commercially available PEO are electrically neutral in aqueous media, an issue of paramount importance in cases when PEO is used as a brightener for the electroplating of bright copper coatings. Viscosimetric measurements were used for the resolution of this problem. The choice was based on the fact that charged polymers with a flexible chain have a larger size of the chaotic (Gaussian) sphere, due to the electrostatic repellent force among the identically charged links. Aqueous solutions of polyethylene oxide produced at NEOCHIM (Bulgaria) were used for the assessments. The molecular mass of the product, determined by us viscosimetrically was 1.6 × 10 o. The basic PEO solution with a concentration 1 g dm -3 was prepared by dissolving the dry product in double-distilled water cooled down to 4°C; this was done with continuous stirring using an electromagnetic stirrer at 300 r.p.m, for 24 h. The doubledistilled water was used for all cases of further measurements. The viscosimetric measurements were carried out with a modified Hoeppler viscosimeter at shear stress S within the range 0.736-1.96 kPa at 0.24 kPa steps. The temperature of the solutions during the study was kept within the limits 20 + 0.05 °C using a water thermostat. The concentration of the investigated polymer in the solutions was changed within the range 1.0-0.1 gdm -3 and the concentration of NaC1 within the range 0.05-1.2 M. The time t required for the shift of the piston (spherical ball) at a certain distance in the test tube containing the investigated solution was measured.