One-Shot System

In the single-step system, the entire reaction takes place when all three basic components plus catalysts and pigments are mixed together. Careful use of catalysts enables the preparation of the prepolymer and the subsequent chain extension to take place in one step. As all the reactions are exothermic, heat is liberated and must be removed otherwise, part distortion will take place. 

The commercial use of this system requires the careful metering and temperature control of the various streams. As a result of the heat liberated, this system is best suited to long runs of thin wall products. 

The systems may be either a three-dimensional network based on covalent bonding or linear extended chains bonding through hydrogen bonds. 

The high exotherm and the number of feeds have led to the popularity of the quasiprepolymer variation of the one-shot technique. Quasiprepolymers are a version of the standard prepolymer method, where some of the polyol is reacted with an excess of diisocyanate. This is later reacted with the remainder of the polyols, including the chain extender and some catalysts. The advantage of this scheme is that the exotherm is spread between the preparation of the quasiprepolymer and the final cured part. In MD1 systems, BDO is often used as the curative. As the molecular weight of BDOs is low, the amount added is low. By dissolving it in the polyol, a more even mix ratio can be obtained. 

The polyol, the chain extender, and any catalysts are mixed and stored as a separate item. The second item, the diisocyanate prepolymer, is kept as a B part until the material is ready for use. When the two parts are mixed, the chain extension and cross-linking take place simultaneously. Methylene diisocyanate and a catalyst such as an organic tin or bismuth salt provide the 

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Because of their importance in foam manufacture, one-shot systems are dealt with in more detail in Section 27.5. With solid materials the systems are used for... 

On some machines both hand-operated and electrically timed one-shot systems may be in use, the manual system being reserved for those components needing infrequent attention (once a day, for example) while the automatic systems feeds those parts that require lubrication at relatively brief intervals. 

Example 10. Two-Component, Nonsagging, Polyurea Structural Adhesive. This example is an all-urea formulation unusual for a 100% solids, hand-castable system. It is also a two-component, one-shot system designed to be nonsagging so that it may be applied to nonhorizontal surfaces without dripping or running. This and similar examples are described in U.S. Patent 5,654,085. See also Guether et al., presented at Polyurethanes Conference 2000, October 8—11, 2000 CRC Press Boca Raton, FL, 2000. 

These are liquid systems that can be produced either in a one shot system (i.e., the diisocyanate, polyol and chain extender reacted in one stage) or, more usually, as a prepolymer which is chain extended and crosslinked at a later stage. 

Siroc [Silicate rock] Also known as the one-shot system. A chemical grouting system for hardening ground formations. Aqueous solutions of sodium silicate and formamide are mixed and injected into the ground the formamide slowly reacts with the silicate, precipitating hydrated silica, which binds the soil particles together. Invented in 1961 by the Diamond Alkali Company. See also Joosten. 

Chain extension/cross-linking to complete production of polyurethane One-Shot Systems... 

Bismuth catalysts promote the isocyanate and OH reaction from the isocyanate side. This has the effect of reducing the water reaction and hence reduces the liberation of carbon dioxide gas. They are particularly useful in controlling the reactions when used in one-shot systems. 

To determine the effect of the polyol primary content on the processability of a one-shot system, two 4000-MW, ultra-low monol PPG diols, which were EO-capped to obtain primary contents of 80 and 87 percent were prepared. These were compared with a... 

The previous studies led to the development of three products, a 2250-MW diol (Acclaim Polyol 2220), 4000-MW diol (Acclaim Polyol 4220) and a 6000-MW triol (Acclaim Polyol 6320). Table 9.4 shows the typical properties of these new higher-reactivity, ultra-low monol PPG polyols. The behaviour of these products in one-shot systems is discussed below. 

To produce an elastomer the dihydric glycol in Fig. 2.2 must be linear in nature and react with the diisocyanate to produce the prepolymer intermediate. Alternatively, the one-shot system of Fig. 2.1 may be utilized as given in Fig. 2.3. 

One-shot systems Polymeric glycol Diisocyanates Chain extender Catalyst system... 

Fig. 6.2. The basic principle of a RIM one-shot system (from Sweeney, 1979).

Continuous polymerization using the one-shot system technique with high catalyst concentrations to produce a very short in-plant reaction time and no post-curing. 

Prepolymers One-shot systems Thermoplastic Millable gums Castable liquids Reaction injection-moulded and cast systems Melt-processed by injection moulding or extrusion Conventional rubber processing... 

One Shot System Prepolymer System Quasi-prepolymer System... 

In the one-shot system the isocyanate forms one stream and all the remaining components form the other. 

Silane cross-linking - specifically the one-shot system - employs a three-component mix (of peroxide, silane, and tin catalyst, either in the form of liquid of dry masterbatch) that is added separately to the compound during extrusion. The reaction is in two stages, the temperature of extrusion being used to decompose the peroxide in order to react the silane molecule onto the polymer backbone. 

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