TECHNOLOGY

Self-adhesive Polymeric Coatings Have Nonstick Surfaces

Thin films reduce drag at solid-fluid interfaces; offer such uses as coatings for boat hulls, dental structures, and cardiovascular prostheses

One of life's excruciating tasks— scraping barnacles and other ma­rine aggregations off boat hulls— may soon lose its pain. A polymeric material developed by a Tampa, Fla., scientist is proving effective in tests as a coating that resists adherence of marine organisms and also re­duces drag.

However, notes Keith Kent, pres­ident of Kent Integrated Scientific Systems (KISS), use of the material as a marine coating is only part of the story. The technique he devel­oped prepares self-adhesive poly­meric coatings that readily adhere in thin films to most solids—requir­ing no primers or other pretreat-ments—and produce a highly sta­ble, nontoxic, nonstick surface that reduces drag at solid-fluid interfaces.

He envisions a vast variety of possi­ble applications beyond marine coat­ings, including coatings for cardio­vascular prostheses and dental struc­tures, wood preservatives, and car and airplane coatings.

Kent started the small Tampa firm last December to develop products based on research he began in 1979. He has training in both chemistry (a B.A. degree) and dentistry. Col­laborating with him are chemists Robert E. Baier of the State Univer­sity of New York, Buffalo; and Herman Gucinski of Anne Arundel Community College, Severna Park, Md. Kent discussed some of his work at American Chemical Society national meetings, both last month and in March 1983.

Kent's research on the coatings began when as a dentist he tried to understand the physical and chem­ical principles determining the bond strengths of prosthetic skin adhe-sives. His specialty, maxillofacial prosthetics, involves providing ar­tificial replacement parts for miss­ing structures in the head and neck region, usually using silicones and other high-molecular-weight poly­

mers that are relatively inert and biocompatible. Prosthetic skin ad-hesives are frequently used to bond the prostheses in place, instead of, or in addition to, mechanical reten­tion. However, the inertness that makes the polymers suitable for prostheses also means that the ad­hesive cannot bond chemically to the prosthetic material, but must in­stead be bonded mechanically.

Kent sought methods of augment­ing the prosthesis-to-adhesive and adhesive-to-skin bond strengths. His work led to development of a new intrinsic prosthetic skin adhesive. Control and modification of poly­merization conditions—with resul­tant changes in the surface chemis­try and character—also led to mate­rials that can selectively bond to most substrates without use of caus­tic or highly reactive reagents, such as the etching and bonding agents now required for silicone polymer bonding. These nontoxic, biocom­patible materials at the same time selectively resist surface interactions, forming a nonadherent interface that can serve as a fouling-resistant or fouling-release surface, with re­duced drag and altered surface wettability.

Kent will not reveal details of the polymer preparation and structure. KISS is seeking patent protection for the materials. However, the ma­terials are made by modifying cross-linked high-molecular-weight poly­mers. He has worked mainly with silicones and polyurethanes—both implantable medical grades—but he says the chemical formulat ions would work as well with polyethers or other high-molecular-weight crosslinked polymers.

What he does is to modify the chemistry of the polymers by "ma­nipulating the prepolymerization process." This affects the way a

Barnacles and other marine growths from nine months in ocean are easily wiped off KISS-COTE-coated plate (left), resist removal on unco at ed plate

44 October 14, 1985 C&EN

polymer—for example, a silicone— polymerizes, and results in a differ­ent crosslinked configuration than that found in normal silicones (for example, a more methylated sur­face). This process alters the surface energy, changing surface behavior: For instance, a silicone surface can be made pe rmanen t ly tacky. He also can produce " te thered" sur­face-bound polymers—a surface-extended network of crosslinked chains with loose ends reaching into, and thereby controlling, flow/ adhesion properties in the liquid phase.

The polymers can be readily mod­ified with additives and/or thin­ners to change their color, consis­tency, and surface chemistry. The silicone polymer is made as a wax, paint, and jelly. The wax is just wiped on and wiped off, leaving a very thin film.

The first practical application is as a marine coating, which Kent hopes to market under the name "KISS-COTE" (he is seeking trade­mark approval). Current antifoul-ing coatings act by presenting a tox­ic surface to marine organisms. By contrast, KISS-COTE presents a nonstick, slippery surface, on which the organisms cannot readily colo­nize. Thus, coated glass fiber test plates that have been suspended in the Gulf of Mexico for nine and 15 months can easily be wiped clean of barnacles and other growths with a bare finger; uncoated plates can­not be cleaned even by scraping with a sharp knife. Moreover, un­like current coatings, KISS-COTE re­quires no primers or other pretreat-ment, even on glass fiber boats.

Kent is also studying other appli­cations. In limited animal trials, a polymer coating reduced sticking of blood cells and bacteria in small-diameter artificial blood vessels. The silicone polymer is permeable to oxygen, and so he is working with a local fence firm to test use as a wood sealant and preservative. Use in surgical dressings is another sug­gestion. Use in toothpaste and in crown and denture coatings, to pre­vent sticking of plaque and food, looks promising. And coating air­planes to keep off ice, insects, and other debris is a possibility.

Richard Seltzer, Washington

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