Segmented polyurethane adhesives

Figure 1. The dynamic viscosity (G"/w in pascal seconds) of Halthane 73-18 segmented polyurethane adhesive increases with time until the chemorheology of cure is complete. Cure curves for four different temperatures show a positive temperature coefficient which should be proportional to the overall reaction rate.

Kawamoto, Y, Nakao, A., Ito, Y, Wada, N., Kaibara, M. Endothelial cells on plasma-treated segmented-polyurethane adhesion strength, antithrombogenicity and cultivation in tubes. J. Mater. Sci. Mater. Med. 8(9), 551-557 (1997)... 

Ishihara K, Hanyuda H, and Nakabayashi N. Synthesis of phospholipids polymers having a urethane bond in the side chain as coating material on segmented polyurethane and their platelet adhesion resistant properties. Biomaterials, 1995, 16(11), 873-879. 

Lee and Matsuda modified a segmented polyurethane film with a dithio-carbamate moiety and then initiated the polymerization of (ethylene glycol) methacrylate and N,N-dimethylacrylamide [35]. The resulting films were hy-drophihc and were shown to inhibit adhesion of platelets. Such films could be useful as anti-coagulant substrates for devices implanted in vivo. 

Merrill and Salzman have developed PEO soft segment polyurethanes and indeed have demonstrated minimal adsorption of blood proteins and minimal platelet adhesion on such surfaces121). Nagaoka et al. have studied various methacrylate copolymers with PEO side-chains of varying lengths and showed a direct correlation between minimization of platelet adhesion with increased PEO side-chain length and surface... 

For instance, the modification of silicone rubbers, poly-(tetrafluoroethylene), polyethylene, and segmented polyurethanes by ionic attachment of heparin was shown to result in a decrease of platelet adhesion onto these polymers71 74 75. A similar... 

Figure 4. The large broad "maximum" in the loss tangent isotherm of 73-19 polyurethane adhesive at 40 C is attributed to hard segment development. This peak is not observed above 50 C because the hard segment glass transition temperature has been exceeded.

Seven polyurethane adhesives have been developed at Lawrence Livermore National Laboratory (LLNL). These adhesives, designated Halthanes were synthesized because of OSHA restrictions on the use of the curing agent methylene bis(2-chloroani1ine). Four of the Halthanes were made fromLLNL-developed 4,4 -methylene bis(phenylisocyanate) terminated prepolymers cured with a blend of polyols three were made from an LLNL-developed prepolymer terminated with Hylene W and cured with aromatic diamines. In this paper we report the dynamic mechanical and thermal behavior of these seven segmented polyurethanes. 

Figure L The low-temperature dynamic mechanical spectrum of Halthane 73-14 is typical of the 73-series polyurethane adhesives. Two secondary relaxations, Tp and Ty, are shown as peaks in the loss modulus at —100° and —150°C. The soft segment glass transition, Tg(SS), occurs at about —50°C. The frequency of oscillation was held constant during the measurement at 0.1 Hz.

There are several ways of changing the properties of segmented polyurethane copolymers. In this study, the chemical structure of the hard segments was changed to adjust the modulus of the adhesive. Further fine tuning is possible by varying the concentration of the different blocks. For example, the 87-series adhesives have a lower modulus than the 88-series adhesives because their hard segment concentration is lower. Studies of concentration effects (16) have shown that much wider variation of modulus is possible tTian was achieved here. 

When each of the acrylate or methacrylate polymers was preincubated with whole plasma, the platelet reactivity of the surfaces upon subsequent exposure to whole blood decreased significantly (Fig. 3). On the other hand, with many other polymers this effect of plasma was not seen. Of 20 varieties of segmented polyurethanes examined, none showed this behavior (22), and platelet adhesion to polystyrene was also unaffected by plasma pretreatment ( ). The phenomenon of plasma-induced passivation of methacrylate and acrylate polymers presumably involves selective adsorption of specific plasma proteins by the surfaces and/or a particular alteration of the adsorbed protein once bound. 

Solvent-borne adhesives represent the majority of the volume in the packaging market, with both one- and two-component systems being used. Waterborne polyurethane adhesives are a much smaller segment that has been driven by environmental considerations. Growth has slowed in recent years because of generally inferior performance compared to solvent-based adhesives and because most of the major converters have already made capital investments in solvent recovery systems. 

Textile fibers (cotton, silk, wool, hair, rayon, nylon, polyester, aramid, etc.) Structural materials (lumber, composites, poly(oxymethylene), PVC, nylon, etc.) Rastios (polyethylene, polypropylene, polytetrafluoroethylene, polyoxide, etc.) Adhesives (glues, epoxies, polyvinyl alcohol, synthetic rubber, segmented polyurethanes, etc.) Biological materials (the basic molecules, carbohydrates, proteins, and DNA)... 

FTIR spectroscopy has proven to be particularly useful in gaining an understanding of the biocompatibility phenomenon. It is believed [746, 841, 856, 857] that protein adsorption is the initial step in the interaction of blood with implanted biomaterials, followed by adhesion of cells and subsequent tissue attachment. This implies that the substrate surface characteristics influence the process, which was confirmed by ATR studies of albumin adsorption on calcium phosphate bioceramics and titanium [763] and segmented polyurethane [764], albumin and fibrinogen on acetylated and unmodified cellulose [765, 766], poly(acrylic acid)-mucin bioadhesion [767], polyurethane-blood contact surfaces [768], and other proteins on poly(ester)urethane [769], polystyrene [767, 771] and poly(octadecyl methacrylate) [771] and by IRRAS study of adsorption of proteins on Cu [858]. Another branch of IR spectroscopic studies of protein adsorption relates to microbial adhesion (Section 7.8.3). 

Aran-Ais E, Torro-Palau A.M., Orgiles-Barcelo A.C., Martin-Martinez J.M., Characterization of thermoplastic polyurethane adhesives with different hard/soft segment ratios containing rosin as an internal tackifier, J. Adhes. Sci. TechnoL, 16(11), 2002, 1431-1448. 

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