Polyurethane -urea

In general, polyurethane urea are always created when diamines are used instead of diols as chain extenders during the synthesis of polyurethanes. This measure changes the hard segment of the resulting polymer molecule. The result is polyurethane urea instead of PUR. If aliphatic diisocyanates, macrodiols, and diamines are also involved, aliphatic polyurethane urea is created. If an aliphatic polyester (M = 1000 to 4000 mol) is used as the macrodiol, we speak of aliphatic polyester-polyurethane ureas [953]. 

Aliphatic polyurethane-urea can be manufactured in pellet form in reaction extruders, or in the form of aqueous dispersions. Compared to TPUs, the influence of the urea hard segment in polyurethane urea on biological degradability is not clear, Table 5.138. The entire polymer is rendered non-biodegradable when a non-degra-dable hard segment is integrated [953]. 

Adipic acid/butanediol/neopentyl glycol HDI-lPDI-mix/lPDA 

The available assessments regarding FIFE and PCTFE vary some mention termite attack, others classify huoropolymers as resistant [32]. 

FIFE is no longer used as material for hip joint sockets because of excessive wear. Expanded FIFE is used for blood vessel replacement for which good results have been published for large-lumen vessels however, assessments of narrow-lumen vessels are controversial [1003]. 

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Siloxane-urethane segmented copolymers, which have very good mechanical, fatigue and surface properties 370,377 or their blends with conventional polyurethane-(ureas) have been successfully used in the production of blood pumps, intra-aortic balloons and artificial hearts 200,332,370,376,377). 

Spaans, C.J., Belgraver, V.W.. Rienstra, O.. De Groot, J.H., Veth, R.P.H., and Pennings, A.J., Solvent-free fabrication of micro-porus polyurethane amide and polyurethane-urea scaffolds for repair and replacement of the knee-joint meniscus. Biomaterials 21 2453-2460, 2000. 

Diamines may be introduced as short chain extenders. As the amine reacts rapidly (Eq. 2.23), hindered aromatic amines must often be used to allow a controllable reaction. Polyurethane ureas are formed. 

Step Non-linear Network Polymers Epoxy resins Melamine Phenolic Polyurethanes Urea... 

Figure 11.9 13C-NMR spectrum of segmented polyurethane-urea, observed at...

Block copolymers were developed rapidly in the 1960s when living anionic polymerization was first utilized to synthesize triblock thermoplastic elastomers or elastoplastics. At the same time, step or condensation polymerization to produce thermoplastic polyurethanes, urea-urethane spandex fibers, and later more specialized materials, such as the semicrystalline polyester-polyether copolymers were developed [10]. Imide block or segmented copolymers utilizing... 

Several studies have been published in recent years on the properties of RIM polyurethanes and polyurethane-ureas (1-7). Unlike most studies, however, we have restricted our attention to simplified linear systems in order to establish the effect of reaction rates and mold temperatures on the phase separation and molecular weight of segmented polyurethane elastomers produced by RIM(6). 

Polyesters, polyetherimide, melamine-formaldehyde, polyurethanes, polyurethane-ureas and polyamides (nylons) are examples of condensation polymers prepared by REX. " Because a small molecule is produced in condensation reactions, vent ports are employed. Between the ports are melt sealing screw sections, to prevent back mixing of volatilizing melt. Sealing screw sections are constructed by a right handed-left handed sequence of screw elements. Another chemistry feature of step-growth reactions is their sensitivity to errors in stoichiometric feed proportions. This poses problems with solid feed materials, which are normally converted to liquid form for more... 

Demir et al. prepared polyurethane urea copolymer solution in DMF and observed that the average fiber diameter (AFD) increases with the solution concentration as given by AFD = (Conc.)3. A trimodal distribution of the fiber diameter has been observed with fiber diameter varying from 7 nm to 1.5 pm (Demir et al. 2002). 

Polyurethane-urea microcapsules were prepared by the interfacial polycondensation of methylene bis(phenyl isocyanate), hexamethylene diamine and anionic sodium hgnin sulphonate, as the emulsifying agent, and 2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide, as a herbicide. The morphology amd microstractuie of these microcapsules were investigated by TEM and scanning electron microscopy and the effect of caldrun chloride on the stabihty of the microcapsule stractuie examined. 22 refs. 

Urea linkages have been monitored during the extrusion production of a polyurethane-urea, through doping with a fluorescent aromatic diamine chain extender, whereas soluble poly(arylene etherjs, thioethers and sulfones have been synthesized which emit strongly in blue and red regions. Brownian dynamics have been used to determine the distribution of fluorescent resonance... 

Synthesis and Modification. A series of polyurethanes and polyurethane-ureas of varying degress of hydrophilicity and hydrophobicity and mechanical property were synthesized. The polymers were prepared by a solution polymerization method and consisted of three components a polyether, a diisocyanate, and a chain extender. In our studies, polyurethanes (Table I) were based on a carbowax (polyoxyethylene glycol), MDI (methylene bis-4-phenyl isocyanate) and 1,5-pentanediol. Polyurethane-ureas (Table II) were obtained by substituting the chain extender from a diol to a diamine. The polyurethane-ureas (Table II) were obtained by changing the chain extender from a diol to a more reactive diamine. The polyurea-urethanes (Table III) were obtained by using a diamine terminated polyether instead of the carbowax. 

The types of polymers in current use are somewhat limited and are mainly poly(dimethyIsiloxane), polyethylene, polytetrafluo-roethylene, poly(methyl methacrylate) and derivatives, poly(ethylene terephthalate), poly(vinyl chloride) [plasticized] and some polyether polyurethane ureas. A large number of other polymers are being studied experimentally. Because of the wide diversity of uses, each of which has very specific requirements, it is not possible for any single polymer to be the only material used in medical applications. In the past, medical applications were usually attempted with a commercial grade of a polymer, but this... 

Most blood vessels in the body are smaller than 4 mm, and no satisfactory replacement currently exists. The most promising materials seem to be certain polyether polyurethane ureas (PEUU) (48, 49) and some hydrogels (50). Both materials show good blood compatibility, and patency rates (in dogs) in excess of 75% have been reported for the PEUU system (49). Human studies have not been made, to date, with either material, but the PEUU material is about the same as that used in the artificial heart. 

L. Salzman, E. W. Merrill, E. W. XPS Analysis of Segmented Polyurethane-ureas Assessment of Surface Activity toward Blood Platelets, in press. 

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