Urethane systems

Urethane sealants Urethane systems Urethane TPE Urethritis, nonspecific... 

N. Barksby and G. L. Aden, "Low Monol Polyols and Their Effects iu Urethane Systems," Polyurethanes World Congress 1993, Vancouver, B.C., Canada, Oct. 10—13, 1993. 

There are many suppHers of urethane systems in the United States. The TSE Company suppHes the mbber form many companies supply the prepolymer forms. It is estimated that close to 68,000 t of these mbbers are used in the United States if aU forms are included. Uses include sport wheels (roUer blades, ski wheels) printing, paper, and steel processing roUs gears pump liners appHance components and soHd industrial tires. 

Low viscosity urethane polymers have been prepared from castor od and polymeric isocyanates (82). These low mix viscosity systems are extremely usehd for potting electrical components where fast penetration without air voids, and fast dispensing cycles are desirable. Very low viscosity urethane systems containing castor polyols have been prepared for use in reclaiming water-logged buried telephone cable and for encapsulating telephone cable sphces (83—86). 

The unblocking temperature usually refers to the temperature at which the blocked urethane system must be heated for 30 min in order to achieve cure. The reaction can be accelerated by curing at higher temperatures and/or by the addition of catalyst, as shown in Fig. 6 [62]. Common urethane catalysts like dibutyltin dilaurate are known to decrease the unblocking temperature. 

Moisture-curable urethane systems (one-pack) can be considered as two-component systems which use atmospheric moisture as the second component. One-pack urethane coatings can be produced that are similar in physical properties to the two-pack systems for almost all applications. These highly complex systems can have a great deal of flexibility. Claimed advantages are a one-pack system, rapid cure, even at low temperatures, excellent chemical and abrasion resistance and good flexibility. Although these systems have been available for some time in other countries of Europe, they are only recently beginning to be of interest in the UK. 

De Groot JH, de Vrijer R, Pennings AJ, Klompmaker J, Veth RPH, and Jansen HWB. Use of porous polyurethanes for meniscal reconstruchon and meniscal prosthesis. Biomaterials, 1996, 17, 163-174. Borkerhagen M, Stoh RC, Neuenschwander P, Suter UW, and Aebischer P. In vivo performance of a new biodegradable polyester urethane system used as a nerve guidance channel. Biomaterials, 1998, 19, 2155-2165. 

Borkerhagen M, Stoh RC, Neuenschwander P, Suter UW, and Aebischer P. In vivo performance of a new biodegradable polyester urethane system used as a nerve guidance channel. Biomaterials, 1998, 19, 2155-2165. 

The majority of water-based UV systems are currently being used in the cabinet industry. Water-based UV coatings should be a blend of different resin systems such blends offer certain benefits. Urethane systems offer excellent clarity, hardness, and flexibility. Acrylic resins are easy to apply and offer quick water evaporation. 

There are relatively few direct transmission, electron microscopy (TEM) studies of domain structures in polyurethanes (3-7,13,14,15). No distinct micelle-lamellae platelets have been observed in the urethane systems thus studied. Instead, the domain structures which have been observed generally appear as isolated equiaxed grains 30-500 A in diameter (4,13,14,15). Randomly oriented fibrils with lateral dimensions of 300-600 A have been observed in a polyether/MDI/BDO system (3,6). It remains to be seen what relation the equiaxed grains (domains) and the fibrils observed by transmission electron microscopy have with the micelle-lamellae structures inferred from WAXS and SAXS (12,16). 

The reaction times are considerably shorter than those encountered with most urethane systems, but the system remains fluid during the rise and the flow is even and controlled. 

Compatibility It Is highly desirable and often mandatory that IMR agents be compatible, both physically and chemically with the chemicals of the urethane system. This means that the IMR agent should be compatible with either the B-side components (polyols plus chain extenders), or the A-slde Isocyanate. Obviously, the reactive nature of isocyanates with compound having an active hydrogen, limits the choice of compounds to those which are non-reactlve, that is, chemically Inert toward isocyanates. 

When a molded part doesn t release, the essential problem (the fact that It sticks to the mold) Is one of adhesion. Thus, If release Is to be achieved, adhesion must be prevented. For most molded urethane systems there are four factors which can affect adhesion, thus release ... 

It has generally been observed that urethane systems, which are cured on the surface of some low energy materials, are also free from adhering to them, i.e. they are self-releasing. Materials which show this characteristic relative to urethanes in a very effective way include at least three different types of plastics polytetrafluoroethylene, polyethylene, and polypropylene. These materials all have a defined critical surface tension sc less than about 30 dynes/cm. Assuming that this value is near, the liquid vapor surface tension lv value of an effective IMR urethane systems, then the work of adhesion as given by Equation 4 is as follows ... 

The ability for an IMR agent to impart release to a given urethane system is a difficult property to quantify and compare. This requirement becomes dependent upon many processing and chemical factors, such as ... 

Reactivity Faster processing of urethane systems has been... 

Nucleation Most elastomeric urethane systems are molded to a... 

Hazard Toxic by inhalation. Damaging to eyes. Use Stabilizers in polyester and urethane systems, intermediate for textile chemicals and pharmaceuticals. 

UrethHall [Hall], TM for polyester polyols for urethane systems that are fluid and pourable at room temperature and are based on chemistry completely different from the traditional adipate polyesters. Available in 25 different variations of glycol base, hydroxyl number, or molecular weight. 

F. Florio, Catalysis of urethane systems, in Handbook of Coatings Additives, 2nd Edn 1. Florio and D. Miller (Eds), Marcel Dekker, New York (2004). 

Problem 5.38 Calculate the sol fraction and the degree of cross-linking in the urethane, networks formed by stepwise polymerization of 2-hydroxymethyl-2-ethyl-l,3-propanediol and 1,6-hexamethylene diisocyanate to 90% conversion of the hydroxyl groups. Compare these properties for two urethane systems with (a) r = 1 and (b) r = 0.75, where r is the mole ratio of hydroxyl to isocyanate groups. 

Aromatic isocyanate tends to react faster than aliphatic isocyanate. The reactivity is also dependent on factors such as sterlc hinderance, temperature, catalysts and competing reactions. Isocyanate reactions found in a urethane system are shown on Table 1. 

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