Prepolymersoffer an attractive approach allowing one to prepare cast systems, especiallyelastomers, from entirely liquid components. In order to obtain a finishedproduct that is resistant to water, damage from heat and chemicals isessential, especially for high-volume production. The most effective method forcontrolling these conditions in the manufacture of such materials aspolyurethane prepolymer is a processcalled thermo-physical conversion. This involves subjecting the materials toextremely high temperatures and forcing them to develop stresses and strainsthat are favorable to the development of the polymer. There are three types ofthermo-physical conversion reactions that may be used to create isocyanates andcoatings:
Oneparticular advantage with regard to the preparation of polyurethane prepolymermixtures is that the mixtures can be produced with relative ease. There areseveral procedures on how to mix these mixtures. The most preferred onesinclude: direct injection of the mixtures into the mold, which calls for theinjection of the mixtures at a very high speed; stirred mixture of the mixtures(sometimes with the help of a stirrer) and then pouring the mixture into themold at a low speed. If these procedures are followed then there is no need tomix the mixtures in order to prepare polyurethane. The mixing is done only onceand then it is applied uniformly in the mold.
Anotheradvantage with regard to the polyurethaneprepolymer formulations is thatone may use them even if the production process does not call for theproduction of polymer mixtures. This is because the polyurethane itself doesnot require any further processing to prepare the final product. When one usesthe polyurethane prepolymer it calls for a final temperature of more than 300degree Fahrenheit and this calls for the use of the heat sealers in the moldsin order to seal the molds. Thus one may be able to say that the polyurethaneis prepared in the present day through the process of polymerization and inthis process it has been converted into a thermosetting polymer compound thatis ready for use in the manufacturing industries.
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