Polyurethane Modified Materials

The promising results in blood compatibility of heparinized-PUs demonstrated that these new polymers reduce thrombus formation compared to nonheparinized PUs. Furthermore, the residual bioactivity of heparin was found to be approximately 25%, slightly higher than those reported elsewhere [143]. 

Other approaches with various antithrombotic drugs or molecules such as urokinase derivatives [144], prostacyclin [145], ADPase [146], dipyridamole [147], and hirudin [148] were developed, but none of them have in-vivo or clinical studies and are still being investigated. 

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Handbook of Polymers for Pharmaceutical Technologies 12.5.3 Polyurethane Modified Materials... 

Compositions of Polyesters, Polyurethanes, Modified Phenolic Resins and Related Materials with Dicyanates... 

ASTM D 4889-88 Standard Test Method for Polyurethane Raw Materials Determination of Viscosity of Crue or Modified Isocyantes, 2 pp (Conun D-20)... 

Christensen L (2002) HOME OF the blue morpho butterfly. New York Times (12 May) Crossland RK, Harlan Jr, JT (1975) Block copolymer adhesive compositions. U.S. Patent 3917607 Davis FJ, Mitchell GR (2008) Polyurethane based materials with applications in medical devices. In Bartolo P, Bidanda B (eds) Bio-materials and prototyping applications in medicine. Springer, New York, pp 27 8. ISBN 9780387476827 Djiauw LK, Icenogle RD (1986) Low smoke modified polypropylene insulation cranpositions. U.S. Patent 4622352... 

Acidity of Crude or Modified Isocyanates D4877 Polyurethane Raw Materials Determination of... 

Viscosity of Crude or Modified Isocyanates D4890-B Polyurethane Raw Materials Determination of Gardner and APHA Color of Polyols D5155 Polyurethane Raw Materials Determination of the... 

Miscellaneous chemicals are used to modify the final properties of rigid polyurethane foams. Eor example, halogenated materials are used for flammabihty reduction, diols may be added for toughness or flexibiUty, and terephthalate-based polyester polyols may be used for decreased flammabiUty and smoke generation. Measurements of flammabihty and smoke characteristics are made with laboratory tests and do not necessarily reflect the effects of foams in actual fire situations. 

Thermosetting-encapsulation compounds, based on epoxy resins (qv) or, in some niche appHcations, organosiHcon polymers, are widely used to encase electronic devices. Polyurethanes, polyimides, and polyesters are used to encase modules and hybrids intended for use under low temperature, low humidity conditions. Modified polyimides have the advantages of thermal and moisture stabiHty, low coefficients of thermal expansion, and high material purity. Thermoplastics are rarely used for PEMs, because they are low in purity, requHe unacceptably high temperature and pressure processing conditions. 

Most of the surface sizes used in North America are modified styrene maleic anhydride (SMA) copolymers. Commercially available materials include Scripset (Monsanto/Hercules Inc.), Cypres (Cytec), Sursize (Akzo Nobel), MSA (Morton), NovaCote (Georgia Pacific), and HTl (Hopton Technologies). Styrene acrylate emulsions that are commonly used include Jetsize and Unibond (Akzo Nobel), Basoplast (BASF), and Cypres (Cytec). Other materials used as surface sizes include acrylonitrile acrylate copolymer (Basoplast, BASF), stearylated melamine resin (Sequapel, Sequa), polyurethane (Graphsize, Vining Chemicals), and diisobutylene maleic anhydride copolymers (Baysynthol, Bayer). 

Polyurethane foams do, however, suffer from one serious disadvantage. Unless modified they bum with copious evolution of smoke and toxic by-products, which has led to a number of fatal fires, particularly in domestic accommodation. To some extent the problem may be reduced by suitable upholstery covering, but as mentioned on p. 775 a number of countries have now made mandatory the use of fire retardent additives. At the time of writing there is considerable activity in the development of new safer systems, particularly in the use of amino materials such as melamine as additives. Further developments may also be expected in the near future. 

Two-component waterborne urethane dispersions are similar to the one-component PUD s in that a polyurethane dispersion comprises one of the two components. The second component is usually a crosslinker from the following classes of materials (a) polyisocyanates, (b) aziridines, (c) polycarbodiimides, and (d) epoxies. Many of the crosslinkers are not inherently water-soluble or water-dispersible. Therefore, they must be modified with surface active agents themselves, so as to become emulsifiable in water. 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

Coal tar-modified polyurethane is a cold-applied liquid waterproofing system. The system by Sonneborn is an example of this approach to waterproofing. It is applied as a liquid at the rate of 10-15 mils/coat. The coating dries hard, but has some elasticity. This material may be attacked by acids in groundwater but can be defended by a protection board. The performance of any liquid-applied waterproofing systems is limited by the capabilities of the applicator (it is difficult to achieve even coats on vertical surfaces). 

Adherent films would not necessarily require formation of covalent bonds at the Interface, since localized lntermolecul u dispersion forces that u e operative In the adsorption of coatings (with good wetting properties) should provide stable interfacial bond conditions. Among candidate materials which could fulfill the requirements of good adhesion and substrate protection from moisture are epoxy-modified polyurethanes and epoxy-siloxane polymers. 

Macromolecules may be classified according to different criteria. One criterion is whether the material is natural or synthetic in origin. Cellulose, lignin, starch, silk, wool, chitin, natural rubber, polypeptides (proteins), polyesters (polyhydroxybutyrate), and nucleic acids (DNA, RNA) are examples of naturally occurring polymers while polyethylene, polystyrene, polyurethanes, or polyamides are representatives of their synthetic counterparts. When natural polymers are modified by chemical conversions (cellulose —> cellulose acetate, for example), the products are called modified natural polymers. 

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