Polyurea dispersions

There are two classes of polyols used in PU synthesis polyesters and polyethers. Approximately 90% of all PUs are manufactured using polyether polyols. Many polyols can be modified to have a higher degree of primary hydroxyl groups, or to contain one of polyurea or PU dispersions.The primary polyols are more reactive and the dispersed polyurea and PU segments serve to increase the crosslinking of the finished PU. Most of the polyether polyols... 

In Chapter 3, the chemistry and technology of the most important oligo-polyols used for elastic polyurethanes fabrication, in fact high MW oligomers (2000-12000 daltons) with terminal hydroxyl groups and low functionality (2-4 hydroxyl groups/mol) were discussed. Polyalkylene oxide polyols (homopolymers of PO or copolymers PO - EO, random or block copolymers), polytetrahydrofuran polyols, filled polyols (graft poly ether polyols, poly Harnstoff dispersion - polyurea dispersions (PHD) and polyisocyanate poly addition (PIPA) polyols), polybutadiene polyols and polysiloxane polyols were all discussed. The elastic polyurethanes represent around 72% of the total polyurethanes produced worldwide. 

A specific example of the process represented by Figure 4b occurs when a multihmctional isocyanate is dissolved in a Hquid, water-immiscible core material and the mixture produced is dispersed in an aqueous phase that contains a dispersing agent. The aqueous phase reacts with some of the isocyanate groups to produce primary amine functionaHties. These amino groups react with unreacted isocyanate groups to produce a polyurea capsule shell (13). 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

The chain extension step may then take place in the water phase. Hydrazine and ethylene diamine are commonly used chain extenders for waterborne urethane dispersions. The isocyanates react with the diamine chain extenders much faster than with the water, thus forming polyurea linkages and building a high molecular weight polymer. More detailed information regarding the synthesis and process of making waterborne polyurethane dispersions is found in Dieterich s review article [58]. 

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

It is also possible to generate microcapsules through interfacial polymerization using only one monomer to form the shell. In this class of encapsulations, polymerization must be performed with a surface-active catalyst, a temperature increase, or some other surface chemistry. Herbert Scher of Zeneca Ag Products (formerly Stauffer Chemical Company) developed an excellent example of the latter class of shell formation (Scher 1981 Scher et al. 1998). He used monomers featuring isocyanate groups, like poly(methylene)-poly(phenylisocyanate) (PMPPI), where the isocyanate reacts with water to reveal a free primary amine. Dissolved in the oil-dispersed phase of an oil-in-water emulsion, this monomer contacts water only at the phase boundary. The primary amine can then react with isocyanates to form a polyurea shell. Scher used this technique to encapsulate pesticides, which in their free state would be too volatile or toxic, and to control the rate of pesticide release. 

Polyurea dispersion polyols (PHD polyols, Polyhamstoff Dispersion polyols) were developed by Mobay Corp. (151). PHD polyols are usually... 

The VR-75 RRIM machine made by Accuratio Systems, Inc. (ASI) was used in this study, and a chromium polished steel mold (220 x 293 x 3 mm) with an aftermixer section was also used. It was equipped with cores for hot water circulation and was controlled at 60°C-70°C. The clamping force was supplied by a simple air bag press. The resin used consisted of a polyurea dispersion in a blend of... 

Encapsulation. Immobilization of enzymes by encapsulation within semipermeable structures dates back to the 1970s. There are three fundamental variations of this approach. In coacervation, aqueous microdroplets containing the enzyme are suspended in a water-immiscible solvent containing a polymer, such as cellulose nitrate, polyvinylacetate, or polyethylene. A solid film of polymer can be induced to form at the interface between the two phases, thereby producing a microcapsule containing the enzyme. A second approach involves interfacial polymerization in which an aqueous solution of the enzyme and a monomer are dispersed in an immiscible solvent with the aid of a surfactant. A second (hydrophobic) monomer is then added to the solvent and condensation polymerization is allowed to proceed. This approach has been used extensively with nylons, but is also applicable to polyurethanes, other polyesters, and polyureas. 

The amine-based Henry reaction catalyst was encapsulated via the interfacial polymerization of oil-in-oil emulsions. PEI was encapsulated by dispersing a methanolic PEI solution into a continuous cyclohexane phase. Upon emulsification, 2,4-tolylene diisocyanate (TDI) was added to initiate crosslinking at the emulsion interface, forming polyurea shells that contain free chains of PEI. The microcapsules crenate when dry and swell when placed in solvents such as methanol and dimethylformamide, suggesting a hollow capsule rather than a solid sphere formation. The catalyst loading was determined to be 1.6 mmol g . ... 

Many of the same basic raw materials shown in Table II for RIM fascia systems are also used in high modulus systems. Additionally, however, polyether polyols "filled" with dispersions of polyureas are used( 2) These are the so-called PHD polyols developed by Bayer AG, the PHD being an abbreviation for Polyharnstoff-Dispersion. These polyols provide the same "filler" effect as the graft polyols (Table II) for increasing the modulus of the polymer without increasing the amount of extender. 

Polymer polyols are defined as very fine and stable dispersions of solid polymers (vinylic polymers and copolymers, polyurea, polyurethanes) in liquid polyethers. Currently polymer polyols represent one of the most important group of polyolic intermediates for elastic polyurethanes [1-10]. 

PHD polymer polyols are a special class of filled polyols developed successfully by Bayer, PHD being the abbreviation of the German name polyharnstoff dispersion or polyurea dispersions [67-69]. PHD polyols contain organic urea, oligomeric or polymeric polyurea, finely dispersed in liquid polyether polyols [67-73]. The difference between PHD polyols and graft polyether polyols is the different nature of the solid polymer dispersed (it is a heterocatenary polymer - polyurea - instead of carbocatenary polymer) which is obtained by another synthetic procedure (polyaddition reaction between a diisocyanate and a diamine instead of radical polymerisation). The reaction between the diisocyanate and the diamine, takes place in situ (reaction 6.19), in liquid poly ether. The resultant polyurea being insoluble in polyether, precipitates in the form of very fine particles ... 

A small part of the -NCO groups of diisocyanate reacts with the terminal hydroxyl groups of polyethers and forms a block copolymer structure, having a polyurea segment chemically linked to a polyether segment, which plays the role of a nonaqueous dispersant and assures the excellent stability of the resulting polyurea dispersion (reaction 6.20) [67, 68]. 

The concentration of this hybrid structure (polyether block linked to a polyurea block) is low, but it is enough to assure a good stability of the dispersion. This very reactive system is based on the big difference in reactivity between primary amines and hydroxyl groups and the -NCO groups of the diisocyanate. Thus the -NCO group reacts 3300 times more rapidly with primary amines than with secondary hydroxyl groups and around 1000 times more rapidly than with the primary hydroxyl groups. 

Very interesting PHD polyols are obtained by the reaction in polyether media of TDI with primary amines and, instead of polymeric polyurea, organic diurea compounds are generated, insoluble in polyethers, in the form of a very fine dispersion. Example of amines used include ammonia, anilines and substituted anilines, and fatty amines (reactions 6.22 and 6.23). 

A very unconventional way to obtain a polyurea dispersion is to react gaseous carbon dioxide, at higher pressures (> 20 MPa) and at around 50 °C, with diamines dissolved in liquid polyether polyols [74] ... 

Hydroxyl-Containing Graft Copolymers and Polyurea Dispersions. Graft copolymers of polyethers containing polyacrylonitrile chains have become available commercially, primarily for the manufacture of flexible foams, although they have also been evaluated in other applications (106-108). 

PHD (polyharnstoff dispersion) or PUD (polyurea dispersion) polyols have been introduced by Bayer-Mobay as an alternative to... 

For waterborne paint systems (especially emulsions used for decorative purposes) defoamers based on mineral oils are often used. In addition to the mineral oil as carrier, these products contain finely dispersed hydrophobic particles (e.g., silica, metal stearates, polyureas) as defoaming components. A small amount of silicone is sometimes included to intensify the defoaming action. For high-quality waterborne coatings in industrial applications, defoamers are used that contain hydrophobic silicone oils as the principal defoaming component instead of mineral oils. They have a better defoaming effect, but are more expensive. In most cases silicone defoamers do not cause the gloss reduction that is often observed with mineral oil products. 

Both interfacial polycondensation and polyaddition involve two reactants dissolved in a pair of immiscible liquids, one of which is preferably water, which is normally the continuous phase, and the other one is the dispersed phase, which is normally called the oil phase. The polymerization takes place at the interface and controlled by reactant diffusion. Researches indicate that the polymer film occurs and grows toward the organic phase, and this was visually observed by Yuan et al. In most cases, oil-in-water systems are employed to make microcapsules, but water-in-oil systems are also common for the encapsulation of hydrophilic compounds. Even oil-in-oil systems were applied to prepare polyurethane and polyurea microcapsules. ... 

Hydrophilic materials can be encapsulated with the inverse minianulsions by using interfacial polymerization such as polyaddition and polycondensation, radical, or anionic polymerization. Crespy et al. reported that silver nitrate was encapsulated and subsequently reduced to give silver nanoparticles inside the nanocapsules. The miniemulsions were prepared by anulsilying a solution of amines or alcohols in a polar solvent with cyclohexane as the nonpolar continuous phase. The addition of suitable hydrophobic diisocyanate or diisothiocyanate monomers to the continuous phase allows the polycondensation or the cross-linking reactions to occur at the interface of the droplets. By using different monomers, polyurea, polythiourea, or polyurethane nanocapsules can be formed. The waU thickness of the capsules can be directly tuned by the quantity of the reactants. The nature of the monomers and the continuous phase are the critical factors for the formation of the hollow capsules, which is explained by the interfacial properties of the systan. The resulting polymer nanocapsules could be subsequently dispersed in water. 

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