Polymeric membranes and other polymer articles having desired surface characteristics and method for their preparation

#The invention relates generally to polymer articles having modified surfaces, such as an essentially hydrophobic polymer article having a hydrophilic surface resulting from entropically-enhanced migration of a miscible, hydrophilic component to the surface of the article.

#A membrane having a hydrophobic core and a hydrophilic surface component is provided as well.

#Control of the surface chemistry of polymeric articles and compositions has technological relevance to a variety of commercially-important areas such as the medical devices industry, personal products, coatings, membranes, etc. Many polymeric articles and compositions that are useful in these areas are defined by a particular type of material because of economic considerations or mechanical requirements. For example, an essentially hydrophobic material might be used for structural reasons where it would be desirable to provide a different type of surface, for example a hydrophilic surface, on the article. Other examples involve imparting a chemical functionality to a surface such as a chelating functionality or other functionality that can selectively remove particular species from solution, or otherwise expose a desired chemical characteristic. While many techniques exist for modifying surface properties of polymers, many involve multi-step processes and/or do not result in thermodynamically or physically-stable incorporation of surface-modifying components.

#FIG. 1 is a schematic illustration of a cross section of a surface of an essentially hydrophobic, prior art polymeric article modified with a low molecular weight component having a hydrophobic portion anchored in the article and a hydrophilic portion facing the surface of the article;

#FIG. 2 is a schematic illustration of an essentially hydrophobic polymeric article of the invention having a compatible, less-hydrophobic, branched component residing at the surface of the article and entangled with the polymer chains of the article;

#FIG. 3 illustrates schematically a branched component of the invention;

#U.S. Provisional Pat. Appln. Ser. No. 60/024,570, filed Aug. 26, 1996 by Mayes et al., U.S. pat. appln. Ser. No. 08/819,610, filed Mar. 17, 1997 by Mayes et al. and PCT Appln. No. PCT/US97/16488, filed Aug.26, 1997, and all are incorporated herein by reference.

#The present invention provides surface-modification techniques for polymeric articles that involve selective segregation of a component of a polymer blend to a surface of the blend to provide desired chemical functionality at the surface. One aspect of the invention makes use of entropic segregation to create a desired surface property. Another aspect involves segregation driven at least in part by entropy. One embodiment of the invention involves surface-functionalized membranes.

#Specifically, the present invention involves techniques for surface segregation, from a polymer blend of a plurality of miscible components, of a relatively higher-cohesive-energy component including a chemical functionality that is desired at the surface. In one set of embodiments, control of the surface chemistry of a polymer can be achieved by designing a surface-modifying polymer component that will be entropically-driven to the surface of the article because of its branched molecular architecture, providing the surface-modifying component with a chemical functionality desired at the surface, and designing the component so that it will be compatible with the base component of the polymer matrix. As used herein, “entropically-driven” is meant to define driven by a force enhanced at least in part by entropy. That is, the surface-modifying polymer component is driven to the surface essentially exclusively by entropic forces, or by a combination of forces at least one of which is entropic. In particular, use of a branched molecular architecture in a component having a chemical functionality desirable at the surface provides a thermodynamic mechanism for the segregation of the component to the surface and a means to achieve a high surface coverage of the component.