Polyurethane prepolymer

In the CSIRO process, a reactive polyurethane prepolymer is appHed to a garment from perchloroethylene. The garment is then pressed and subsequendy steamed in an oven. A second polymer may sometimes be used in conjunction with the prepolymer. When this is employed, the process is termed the Serolan BAP Process (178). A number of alternative treatments are being investigated to achieve finishes that are more environmentally friendly (179). 

Fig, 17. (a) Isocyanate-terminated polyurethane prepolymer synthesis, (b) Moisture cure of isocyanate-terminated polyurethane prepolymers, (c) Side reactions of isocyanate-terminated polyurethane prepolymers. 

OH Polybutadiene Homogeneous hydrogenation [e.g., Ni or CoAriethyl aluminum (or Ru, Rh catalysis)] heterogeneous catalysis (Raney Ni) Hydrogenated mixed 1.4- and 1,2-polybutadienes as heat-resistant polyurethane prepolymers... 

Di-hydroxyl end-capped PPG (18) is an intermediate in the formation of a common polyurethane prepolymer (20). End group functionality of this intermediate is important, as this hydroxyl functionality is modified to form the prepolymer. Any different end group structures could lead to the presence of prepolymer that will not form polyurethane of the desired structure. The desired reaction of the intermediate (18) to form the prepolymer (20) is described in Figure 21. Reaction of one unit of the intermediate (18) and two units of methylene diphenyl 4,4 -diisocyanate (MDI) results in the formation (nominally) of the prepolymer (20). 

Figure 21 Reaction scheme for the reaction of PPG with MDI to form a polyurethane prepolymer.

Figure 26 hi NMR spectrum from MDI/PPG polyurethane prepolymer. Inset shows expansion of spectrum indicating assignment for functionalised end groups of polymer. 

Figure 28 MALDI-TOF mass spectrum from MDI/PPG polyurethane prepolymer. Peaks from functionalised oligomers are annotated with numbers corresponding to those described in the text.

One of the more advanced technical offerings from castor oil is a line of polyester diols, triols, and higher functional polyols derived from 100% castor oil as products for the preparation of polyurethane prepolymers and elastomers [68]. The Polycin line of polyols are prepared by transesterification of ricinoleic acid and derivatives. The producers (Vertellus) offer diol and triol products, as well as a recently developed series of diol and triol glyceryl ricinoleate esters that are stated to be prepared from 100% castor oil, making them fully renewable in content. The products are recommended for coatings, sealants, and adhesive applications. 

Consider the procedure for immobilizing an enzyme using polyurethane technology. A solution of the enzyme is produced in water. The solution is then emulsified with a hydrophilic polyurethane prepolymer. The emulsion is applied to the structural members of a reticulated foam by means of nip rollers. After curing... 

An activated carbon (Nuchar RGC Powder, 879-R-02) was supplied by the Chemical Division of Westvaco, Covington, VA. A slurry of the carbon was made in water and emulsified with a TDI-based hydrophilic polyurethane prepolymer (Hypol 2002, Dow Chemical, Midland, MI). Immediately after mixing, the emulsion was grafted to a 30-ppi polyether polyurethane (Crest Foam T-30, Monachie, NJ.). The amount of carbon was determined gravimetrically to be 29% by weight. 

LeJeune et al. - - investigated this stabilizing effect of immobilization at the expense of activity. They immobilized an organophosphorus hydrolase by emulsifying a solution of the enzyme with a hydrophilic polyurethane prepolymer. They intended to study the enzymatically catalyzed hydrolysis of organophosphate nerve... 

The prepolymer used for this study was an MDI-based preparation (Suprasec 1002) from Huntsman PU, Brussels, Belgium. Immobilization of the enzyme was accomplished by coating the inside structure of a reticulated foam with an acetone solution of a hydrophilic polyurethane prepolymer. A 45-pore/in. reticulated foam cut into sheets 0.25 in. thick was used. The coated reticulated foam was immersed in a catalase solution (5 pg/ml) at 4°C and left in the solution for 1 hour to ensure a complete solution. It is known that both the water and some functionality in the catalase react with the isocyanate groups to cause polymerization (the water-isocyanate reaction) and chain termination (the catalase reaction). Controlling the relative concentrations and temperature permits control of the physical properties of the composite and the ability of the foam to function as an enzyme. 

A hydrophilic polyurethane prepolymer was made according to the procedure taught by Braatz. - The prepolymer was mixed with water at a ratio of 10 parts water to one part prepolymer. The emulsion was poured immediately onto a silicone release liner and allowed to cure for 30 min. It was free of voids and had a density roughly the same as water. For the contraction experiments, the gel was immersed in excess distilled and sterile water for 24 h, tlicii cut with a steel-ruled die into circles 40 mm in diameter. 

THERMOPLASTIC. A high polymer that softens when exposed to heat and returns to its original condition when cooled to room temperature. Natural substances that exhibit this behavior are crude rubber and a number of waxes however, the term is usually applied to synthetics such as polyvinyl chloride, nylons, fluorocarbons, linear polyethylene, polyurethane prepolymer, polystyrene, polypropylene, and cellulosic and acrylic resins. See also Plastics. 

Polyurethane prepolymer was used for the fist time for glueing tissues in 1958 48 . The fundamental notions of adhesion and glueing employed later in developing a large number of technical adhesives had not been elaborated at that time in sufficient detail. 

When a polyurethane prepolymer is reacted with a substance containing a single hydroxyl group such as ethanol or water, reactions will take place that will give off carbon dioxide gas. In thin sections the bubbles may be able to escape or be held by inert fillers. They can also be trapped by pressure-molding the part. 

On completion of the reaction, the material (if not immediately used) must be stored in a clean, dry container. The material of construction must be able to withstand the heat of the material plus any further reheating required. If metal containers are used, they must be lined with an epoxy or similar material that is nonreactive to the polyurethane prepolymer. Any remaining air in the container must be replaced with dry nitrogen gas. All mating surfaces of the closure must be free of the polyurethane prepolymer. 

Keeping the walls clean of buildup is important, because buildup would cause heat transfer problems as the production proceeds. The polyurethane prepolymer builds up in viscosity as the chain length increases and tends to hang onto the wall of the reactor. The heat of the wall will increase the speed of the reaction and hence increase the reaction rate and viscosity. Viscosities in the reactor will be generally between 30 and 4,000 MPa.s at a temperature of approximately 90°C. 

Polyurethane prepolymers are supplied in a variety of sizes, from small 1-kg cans up to 1-ton IBC containers. The available isocyanate (%NCO) level should be marked on every container of conventional prepolymers. Quasiprepolymers do not have individual batch levels supplied, as the overall reaction levels are factory adjusted. 

Polyurethane prepolymers may be liquid or semisolid at ambient temperatures. Before further processing can take place, they must be heated so that the material is fully melted and the viscosity reduced to a point that it can be dispensed successfully. 

The polyurethane prepolymer will slowly increase in viscosity on prolonged heating. It is a result of a chemical reaction between the polyurethane chains. The chemical reaction is irreversible. The available isocyanate is used up therefore, the stated %NCO is reduced. 

Areas where there are hot drums and pipes must be clearly labeled with appropriate signage. Hot polyurethane prepolymer can cause severe bums, and the potential for free isocyanate vapors is very high. 

Dermatitis can result from using a heat glove (nonimpervious) that has been contaminated with either a solvent or polyurethane prepolymer. The same applies to gloves used in the manufacture of prepolymers. 

It must always be taken into account that polyurethane prepolymers are messy materials, and they will cure in the air to form a solid mass. A major precaution would have to be that the gas being delivered to the vessel is at a very low pressure and there is a safe continuous bleeding point. 

In production units where polyurethane prepolymers are used, liquid nitrogen is an option to provide an inert atmosphere in the reactors. The unit should be set up professionally by a supplier and the liquid nitrogen unit properly maintained. 

In order to control the pore texture in carbon materials, blending of two kinds of carbon precursors, the one giving a relatively high carbonization yield and the other having a very low yield, was proposed and called polymer blend method [112], This idea gave certain success to prepare macroporous carbons from poly(urethane-imide) films prepared by blending poly(amide acid) and phenol-terminated polyurethane prepolymers [113]. By coupling this polymer blend method with... 

J.H. Fabris, Novel poly(urethane-amide)s from polyurethane prepolymer and reactive polyamide. Preparation and Properties. Adv. Urethane Sci. Technol., 4, 89-111 (1976). 

Novel, toughened one-component epoxy structural adhesives based on epoxy-terminated polyurethane prepolymer incorporating an oxolidone structure were developed to provide improved toughness, fracture resistance and adhesive properties with good chemical and moisture resistance.21 The hybrid resin cures with a standard latent curing agent/accelerator. 

Figure 4.18. Schematic sketching the experimental procedure used in 3D mesoscale self-assembly. Molding of a polyurethane prepolymer in a PDMS master generated polyhedra. Lubricant was added to the polyhedra in a water-filled Morton flask the use of liquid solder as a lubricant required the covering of selected faces with solder-coated copper tape. Axial rotation of the flask provided the agitation needed to cause collisions between liquid-coated pieces. The schematic depicts the formation and self-...

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