I. INTRODUCTION The behavior of model associative polymers (MAPs), hydrophobically modified poly(ethylene oxide) of molecular weight 2000 to
Water soluble, structure forming polymers have during 6000 g/mol, in aqueous solution has been studied by turbidimetry, recent years been the subject of a never ending increase of differential scanning calorimetry (DSC), and small-angle X-ray investigations. Block copolymers or statistical copolymers, scattering (SAXS) measurements. For the polymer of the lowest consisting of hydrophobic and hydrophilic parts and hydromolecular weight, 2000 g/mol, a complete schematic phase diaphobically modified hydrophilic polymers, are used in widegram has been sketched. The turbidimetric and DSC studies show spread fields from coating and pharmaceutical formulations, that two two-phase regions appear: (1) at low polymer concentration, upon heating above the temperature traditionally called the to enhanced oil-recovery and paper making. Typical examcloud-point temperature (CPT), and (2) at high polymer content, ples of such polymers are the Pluronics block copolymers upon cooling below the crystallisation temperature of the PEO (1), polyacrylates (2), polyacrylamides (3), and cellulose chains. This low molecular weight polymer exhibits a large region derivatives (4), which are modified along the chain, and of liquid crystallinity which is stable from room temperature up end-capped associative polymers (APs) (5, 6). to approximately 60ЊC. The SAXS measurements of the present The major application of APs, specifically of hydrophowork show that this cubic structure is either a simple cubic strucbically end-capped poly(ethyleneoxide), is as an additive ture sc or a body centered cubic structure bcc, but geometrical in water based surface coatings. Relatively low molecular considerations favor the later structure. The distance between the weight formulations containing APs meet the requirements lattice points is compatible with the end-to-end distance of the of viscosity enhancement and more Newtonian flow behav-PEO chains plus the diameter of the hydrophobic microdomain.
ior over a larger range of shear rates than is possible with The radii of the domains which are assumed to be spherical are traditional high molecular weight thickening agents. A vast very close to those obtained for diblock low molecular weight surfactants of C 12 EO y type in micellar or mesomorphic phases. At number of investigations have been carried out in order to higher concentrations, a lamellar phase is formed in equilibrium obtain information of the association mechanism and about with the cubic phase. This phase is of the same type as the lamellar the aggregate size and aggregate shape of various thickener phase formed by unmodified polyethylene oxide. Some additional aggregates. Macroscopic rheological properties, as well as information about the influence of the molecular weight of the properties at molecular level, have been studied both for PEO chains on the limits between the different regions of the simple model systems and for fully formulated paints. In diagrams and on the cubic phase characteristics is presented. addition to viscosity measurements (5-15), static and dy-