Polyurethane-silicone rubber copolymer

Test polymers for visualization studies were polyurethane (Pellethane, 2363-80A, Upjohn), filler-free polydimethylsiloxane (Sil-Med Corporation), two forms of Teflon, sintered (TFE, DuPont) and Fluorofilm (Dilectrix Corporation), and polyurethane-silicone rubber copolymer (AVCOthane 51, AVCO). Samples of 1 cm2 or, for shear studies, 5 X 20 X 0.5-cm sheets, were washed in ionic detergent solution (Alconox) at 60°C for 1 h, rinsed in deionized water, and refluxed in absolute ethanol for 1 h. Materials were dried and stored in a desiccator until use. 

The materials selected for evaluation included three materials currently being used in these applications Biomer (Thoratec Laboratories Corporation, Emeryville, CA), representative of segmented ether-type polyurethanes Avcothane-51 (Avco Everett Research Laboratory, Inc., Everett, MA), a block copolymer of 10% silicone rubber and 90% polyurethane and Hexsyn (Goodyear Tire and Rubber Company, Akron, OH), a sulfur vulcanized hydrocarbon rubber that is essentially a polyhexene. Also selected, because of their easy availability, were Pellethane (Upjohn Company, North Haven, CT), an ether-type of polyurethane capable of being extruded in sheet form, and a butyl rubber formulation, compounded and molded at the National Bureau of Standards. The material thickness varied, but the sheets were generally about 1 mm thick. 

HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HNS NTO NTO/HMX NTO/HMX NTO/HMX PETN PETN PETN PETN PETN PETN PETN PETN PETN PETN RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX TATB/HMX Cariflex (thermoplastic elastomer) Hydroxy-terminated polybutadiene (polyurethane) Hydroxy-terminated polyester Kraton (block copolymer of styrene and ethylene-butylene) Nylon (polyamide) Polyester resin-styrene Polyethylene Polyurethane Poly(vinyl) alcohol Poly(vinyl) butyral resin Teflon (polytetrafluoroethylene) Viton (fluoroelastomer) Teflon (polytetrafluoroethylene) Cariflex (block copolymer of butadiene-styrene) Cariflex (block copolymer of butadiene-styrene) Estane (polyester polyurethane copolymer) Hytemp (thermoplastic elastomer) Butyl rubber with acetyl tributylcitrate Epoxy resin-diethylenetriamine Kraton (block copolymer of styrene and ethylene-butylene) Latex with bis-(2-ethylhexyl adipate) Nylon (polyamide) Polyester and styrene copolymer Poly(ethyl acrylate) with dibutyl phthalate Silicone rubber Viton (fluoroelastomer) Teflon (polytetrafluoroethylene) Epoxy ether Exon (polychlorotrifluoroethylene/vinylidine chloride) Hydroxy-terminated polybutadiene (polyurethane) Kel-F (polychlorotrifluoroethylene) Nylon (polyamide) Nylon and aluminium Nitro-fluoroalkyl epoxides Polyacrylate and paraffin Polyamide resin Polyisobutylene/Teflon (polytetrafluoroethylene) Polyester Polystyrene Teflon (polytetrafluoroethylene) Kraton (block copolymer of styrene and ethylene-butylene)... 

RUBBER (Synthetic). Any of a group of manufactured elastomers that approximate one or more of the properties of natural rubber. Some of these aie sodium polysulfide ( Thiokol ). polychloiopiene (neoprene), butadiene-styrene copolymers (SBR), acrylonitrilebutadiene copolymers (nitril rubber), ethvlenepropylene-diene (EPDM) rubbers, synthetic poly-isoprene ( Coral, Natsyn ), butyl rubber (copolymer of isobutylene and isoprene), polyacrylonitrile ( Hycar ). silicone (polysiloranei. epichlorohy-drin, polyurethane ( Vulkollan ). 

Membrane-reservoir systems based on solution-diffusion mechanism have been utilized in different forms for the controlled delivery of therapeutic agents. These systems including membrane devices, microcapsules, liposomes, and hollow fibres have been applied to a number of areas ranging from birth control, transdermal delivery, to cancer therapy. Various polymeric materials including silicone rubber, ethylene vinylacetate copolymers, polyurethanes, and hydrogels have been employed in the fabrication of such membrane-reservoir systems (13). 

In practice, manufacturers have tried to combine the best characteristics of all insulating materials by using silicone for the lead body, with each cable and coil conductor coated with a fluoropoly-mer and a thin polyurethane layer to cover the entire lead. In this way, is possible to improve abrasion resistance and handling performance. Recently developed copolymer obtained by mixing silicone rubber and polyurethane can also be used for the outer layer. 

As described previously, many attempts have been made over the years to improve the durability and reliability of insulating materials (Fig. 1.32). Recently, good results have been achieved with the copolymer. This is a silicone rubber-polyurethane chemical mesh specifically created for cardiac... 

Pressure sensitive and contact adhesives are made from a variety of polymers including acrylic acid esters, polyisobutylene, polyesters, polychloroprene, polyurethane, silicone, styrene-butadiene copolymer and natural rubber. With the exception of acrylic acid ester adhesives which can be processed as solutions, emulsions, UV curable 100% solids and silicones (which may contain only traces of solvents), all remaining rubbers are primarily formulated with substantial amounts of solvents such as hydrocarbon solvents (mainly heptane, hexane, naphtha), ketones (mainly acetone and methyl ethyl ketone), and aromatic solvents (mainly toluene and xylene). 

Orientations in elongated mbbers are sometimes regular to the extent that there is local crystallization of individual chain segments (e.g., in natural rubber). X-ray diffraction patterns of such samples are very similar to those obtained from stretched fibers. The following synthetic polymers are of technical relevance as mbbers poly(acrylic ester)s, polybutadienes, polyisoprenes, polychloroprenes, butadiene/styrene copolymers, styrene/butadiene/styrene tri-block-copolymers (also hydrogenated), butadiene/acrylonitrile copolymers (also hydrogenated), ethylene/propylene co- and terpolymers (with non-conjugated dienes (e.g., ethylidene norbomene)), ethylene/vinyl acetate copolymers, ethyl-ene/methacrylic acid copolymers (ionomers), polyisobutylene (and copolymers with isoprene), chlorinated polyethylenes, chlorosulfonated polyethylenes, polyurethanes, silicones, poly(fluoro alkylene)s, poly(alkylene sulfide)s. 

In some cases, grafting is used to form the copolymers. Examples of chains combined with PDMS in this way include polyfethylene oxide) fluorinated chains, alkyl acrylates and alkyl methacrylates, polyfvinyl alcohol), polyfether sulfones), and polyurethanes. Grafting has also been used to introduce t-butylamine and t-butylammonium biocidal functionalities, and to improve the adhesion of silicone rubber to polyurethane. In other cases, the siloxane groups are simply placed on the ends of chains, such as onto some polybenzoxazines. ... 

Over the years many fluoroelastomers have been prepared in addition to the materials described earlier in this chapter. These include fluorinated polyurethanes, fluorinated polyepoxides, hexafluoro-acetone/propylene oxide copolymers and polyfluorals. Many of these materials are thermally unstable, a fact which stresses the point that the presence of C—F bonds with their high bond strength is no guarantee of polymer thermal stability. One particular type of fluoroelastomer which is of technical importance, the fluorosilicone rubber family, are however of good thermal stability and are considered together with the silicone rubbers in a later chapter. 

With the development of synthetic elastomers during World War II, new types of adhesives appeared for application to a broader range of substrates and for use at higher temperatures. Styrene-butadiene and butadiene-acrylonitrile copolymers found application in new adhesives. There were also significant concurrent developments in adhesives based on chlorinated rubber, polychloroprene (neoprene), and poly sulfide rubber. Development of carboxylic elastomers, silicone rubbers, and polyurethanes followed. 

Poly(Dimethyl Siloxane) Silicone Rubber, Usually Copolymer with Vinyl groups (VMQ) PolyfDimethyl Siloxane) Copolymer with Phenyl-Bearing Siloxane and Vinyl Groups (PVMQ) Room Temperature Vulcanizing Silicone Polysulfide (ET and EOT) Polyurethane (AU and EU)... 

Not only polydienes but also polyethylene and its copolymers as well as silicone rubbers and polyurethanes can be crossHnked with peroxides. However, a-polyolefins such as... 

There are two types of maxillofacial implants extraoral and intraoral. The former deals with the use of artificial substitutes for reconstructing defective regions in the maxilla, mandible, and face. Useful polymeric materials for extraoral implants require (1) match of color and texture with those of the patient (2) mechanical and chemical stability (i.e., material should not creep or change color or irritate skin) and (3) ease of fabrication. Copolymers of vinyl chloride and vinyl acetate (with 5 to 20% acetate), polymethyl methacrylate, silicones, and polyurethane rubbers are currently used. Intraoral implants are used for repairing maxilla, mandibular, and facial bone defects. Material requirements for the intraoral... 

The elastomer must exhibit a low value of Tg. Among polymers that might be regarded as engineering elastomers the following should be mentioned—butadiene-styrene copolymer (GR-S or SBR), butyl, neoprene, EPR (copolymer ethylene-propylene), nitrile, polybutadiene, thiokol, polyiso-prene, silicon, polyurethane, Hypalon, and EPDM. The internal breakdown by consumption is about 75% synthetic versus 25% natural rubber. Within the family of synthetic elastomers a typical breakdown is about 46% SBR, 19% polybutadiene, 9% EPR, 4% neoprene and 3% nitrile. 

Most compounders use a combination of physical and chemical antiozonants and achieve excellent protection in this way. For more severe ozone-resistance problems, there are, of course, a number of specialty elastomers that are saturated and therefore completely ozone-resistant ethylene/propylene rubber, chlorinated and chlorosulfonated polyethylene, ethylene/vinyl acetate, ethylene/acrylic esters, butyl rubber, SEES, plasticized PVC, butyl acrylate copolymers, polyepichlorohydrin and copolymers, polyetherester block copolymer, polyurethane, and silicone. 

Impact Modifiers. Notched impact strength and ductility can be improved with the incorporation of impact modifiers, which can also lower the brittle-ductile transition temperature and give much improved low temperature toughness. Impact modifiers are rubbers (often olefin copolymers) that are either modified or contain functional groups to make them more compatible with the nylon matrix. Dispersion of the rubber into small (micrometer size) particles is important in order to obtain effective toughening (19). Impact modifiers can be combined with other additives, such as glass fiber and minerals, in order to obtain a particular balance of stiffness and toughness. Modified acrylics, silicones, and polyurethanes have also been proposed as impact modifiers. 

There are many shoe development examples available. These include the use of a low molecular weight silicone oil to swell a silicone polymer [Tokko Kaiho 291110 (1986), trade name Alpha Gel], a gel with polyurethane as the polymer component (product name Solbosen), and a rubber form made of a high styrene, styrene-butadiene copolymer to... 

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