Polyurethane polycarbonate-based

Polyurethanes as Biomaterials. Much of the progress in cardiovascular devices can be attributed to advances in preparing biostable polyurethanes. Biostable polycarbonate-based polyurethane materials such as Corethane (9) and ChronoFlex (10) offer far-reaching capabiUties to cardiovascular products. These and other polyurethane materials offer significant advantages for important long-term products, such as implantable ports, hemodialysis, and peripheral catheters pacemaker interfaces and leads and vascular grafts. 

Although a majority of these composite thermistors are based upon carbon black as the conductive filler, it is difficult to control in terms of particle size, distribution, and morphology. One alternative is to use transition metal oxides such as TiO, VO2, and V2O3 as the filler. An advantage of using a ceramic material is that it is possible to easily control critical parameters such as particle size and shape. Typical polymer matrix materials include poly(methyl methacrylate) PMMA, epoxy, silicone elastomer, polyurethane, polycarbonate, and polystyrene. 

Polyesters produce tough, oil-resistant polyurethanes, with the major drawback being lower hydrolysis resistance compared to polyurethanes made using polyethers. The two newer groups of polyesters (polycaprolac-tone- and polycarbonate-based) both have better resistance to hydrolysis. Their toughness is very close to the basic polyester polyurethanes. Their disadvantage is cost. 

Oligomeric carbodiimides are useful stabilizers for ester based polymers, such as polyesters, polyester based polyurethanes, polyether based polyurethanes, polyether based poly(urethane ureas) and polycarbonates. The scavenging of carboxyl end groups or carboxyl groups, generated in the hydrolysis of polyesters, with carbodiimide prevents hydrolysis of the polymers caused by the catalytic effect of the carboxyl groups. Neumann... 

Commercial petrochemical processes using syngas or carbon monoxide are based on four principal classes of reactions phosgenation, Reppe chemistry, hydroformylations, and Koch carbonylations. Phosgenation is a key step in the manufacture of polyurethanes, polycarbonates, and monoisocyanates. Reppe chemistry is the basis for acetic acid and acetic anhydride production as well as formic acid and methyl methacrylate synthesis. Hydroformylations utilize syngas in the oxo synthesis to make a wide variety of aldehydes and long-chain alcohols. The fourth class of reactions are Koch carbonylations. Koch carbonylations are used commercially to produce neo acids which are specialty products that serve markets similar to 0X0 alcohols. 

Polyurethanes are sensitive to strong acids, strong alkalis, aromatics, alcohols, hot water, hot moist air and saturated steam. The hydrolytic stability of polyurethanes in applications must be considered carefully. However, polyurethanes are resistant to weak acids, weak alkalis, ozone, oxygen, mineral grease, oils and petroleum. There are doubts for the oxidation stability of polytetramethylene ether glycol based polyurethanes. Polycarbonate urethane is a promising substitute with good oxidation stability. 

Table 4.4 Typical Properties of Polycarbonate-based Polyurethane...

Polyurethanes are another class of TPEs. They are a large family of chemical compounds that can consist of ether-based, ester-based, polycarbonate-based or polypropylene-based varieties. A number of copolymers are also included , polyurethanes are combinations of macroglycols and diisocyanates that have been polymerized into tough and elastic materials. TPE polyurethanes have been used for peristaltic pump tubing, parenteral solution tubing and catheters. The tables list the majority of those that are commercially available. Among others are those either of limited supply, available for proprietary use only or that have been successful, but recently discontinued such as ... 

This medical grade TPE polyurethane is the reaction product of an aliphatic diisocyanate, a polycarbonate-based macrodiol, and a chain terminating low molecular weight diol (Tables 4.4, 4.12, and 4.13). 

Available as a dimethyl acetamide solution, this segmented, aromatic, polycarbonate-based TPE polyurethane was designed to mimic Ethicon Corporation s Biomer. The polymer is made from the addition of diphenylmethane 4,4 -diisocyanate to a polycarbonate diol followed by addition of a mixture of chain extenders and a molecular weight regulator. The polymer is believed to be resistant to environmental stress cracking such as that experienced by other polyurethanes coated onto pacemaker leads (Tables 4.4, 4.12, and 4.13). 

Spfrkovi M, Pavlicevid J, Strachota A, Poreba R, Bera O, Kapralkova L, et al. Novel polycarbonate-based polyurethane elastomers composition-property relationship. Eur Polym J 2011 47(5) 959-72. 

Labow RS, Sa D, Matheson LA, Dinnes DLM, Santerre JP. The human macrophage response during differentiation and biodegradation on polycarbonate-based polyurethanes dependence on hard segment chemistry. Biomaterials 2005 26(35) 7357-66. 

The former class includes acrylic copolymers, vinyl acrylics and styrene butadiene, whilst the latter also embraces aqueous polyurethanes, polycarbonates and polyesters. Normally an acid or base functional resin is prepared in solution of a water soluble/miscible solvent, such as butyl glycol or butanol. Upon neutralisation, the resin is dispersed into the water phase and this is sometimes refered to as inversion . 

Matheson L A, Labow R S, Santerre J P (2002), Biodegradation of polycarbonate-based polyurethanes by the human monocyte-derived macrophage and U937 cell systems , J Biomed Mater Res, 61(4), 505-513. 

Acrylic Resins. The first synthetic polymer denture material, used throughout much of the 20th century, was based on the discovery of vulcanised mbber in 1839. Other polymers explored for denture and other dental uses have included ceUuloid, phenolformaldehyde resins, and vinyl chloride copolymers. Polystyrene, polycarbonates, polyurethanes, and acryHc resins have also been used for dental polymers. Because of the unique combination of properties, eg, aesthetics and ease of fabrication, acryHc resins based on methyl methacrylate and its polymer and/or copolymers have received the most attention since their introduction in 1937. However, deficiencies include excessive polymerization shrinkage and poor abrasion resistance. Polymers used in dental appHcation should have minimal dimensional changes during and subsequent to polymerization exceUent chemical, physical, and color stabiHty processabiHty and biocompatibiHty and the abiHty to blend with contiguous tissues. 

Among the polyurethane, polyester, and polyamide thermoplastic elastomers, those with polyether-based elastomer segments have better hydrolytic stabihty and low temperature flexibiUty, whereas polyester-based analogues are tougher and have the best oil resistance (43). Polycaprolactones and aUphatic polycarbonates, two special types of polyesters, are used to produce premium-grade polyurethanes (12). 

Hydrolysis studies compared a polycarbonate urethane with a poly(tetramethyl-ene adipate) urethane and a polyether urethane based on PTMEG. After 2 weeks in 80°C water, the polycarbonate urethane had the best retention of tensile properties [92], Polycarbonates can hydrolyze, although the mechanism of hydrolysis is not acid-catalyzed, as in the case of the polyesters. Polycarbonate polyurethanes have better hydrolysis resistance than do standard adipate polyurethanes, by virtue of the highest retention of tensile properties. It is interesting to note in the study that the PTMEG-based urethanes, renowned for excellent hydrolysis resistance, had lower retention of physical properties than did the polycarbonate urethanes. 

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