Chemistry of polyurethane elastomers

The present book is organized into 6 chapters. Chapter 1 describes general aspects on the chemistry of polyurethane elastomers their origins and development, the principles and synthesis mechanisms, as well as general considerations on the main chemical parameters that define such materials, i. e. diisocyanate, macrodiol and chain extender. Selected considerations regarding the reactivity of diisocyanates, the hydrogen bonding and its dynamic and quantum aspects are also discussed in this chapter. 

The development of polyurethane adhesives can be traced back more than 60 years to the pioneering efforts of Otto Bayer and co-workers. Bayer extended the chemistry of polyurethanes initiated in 1937 [1] into the realm of adhesives about 1940 [2] by combining polyester polyols with di- and polyisocyanates. He found that these products made excellent adhesives for bonding elastomers to fibers and metals. Early commercial applications included life rafts, vests, airplanes, tires, and tanks [3]. These early developments were soon eclipsed by a multitude of new applications, new technologies, and patents at an exponential rate. 

This book is designed as a review of the state of the art but also brings new contributions in highly specialized subjects, in a stiU rapidly moving field the fundamentals of polyurethane elastomers their chemistry and properties and materials choice for formulation development. 

The book reviews aspects from the up-to-date literature focused on these topics including our research. In addition the book records selected results from an international NATO project collaboration between The Department of Engineering Science, University of Oxford and our Romanian laboratory at the Institute of Macro-molecular Chemistry Petru Poni , Iasi. This has made possible an unusually comprehensive study of the structure and important physical properties of polyurethane elastomers—a class of polymer of such great industrial importance. 

Polyurethane in the rubber industry can be used in (1) the thermoplastic elastomer form (TPE), discussed earlier, (2) a two-part liquid system in reaction injection molding (RIM), (3) the cast molding of rubber parts, or (4) as a millable gum that can be processed on a two-roll mill and cured with agents such as peroxides or sulfur, just as with conventional rubber. Although different versions of polyurethane elastomers must be tailor-made for each of these four common applications, the basic chemistry used is very similar in all. 

This chapter introduces readers to the versatility of polyurethane polymers without spending too much time on the chemistry. The next chapter will discuss a more classical view of the molecule and how it is developed. Our point, however, is to present a functional view of this system. We have examined its physical characteristics, focusing our attention on the uniqueness of reticulated foams. All the chemical points we have made apply to all polyurethane polymers, whether they are open-celled foams, closed-cell foams, or thermoplastic elastomers. 

Castable Polyurethane Elastomers is a practical guide to the production of cast-able polyurethane articles. These articles can be as simple as a doorstop to items used in nuclear and military industries. The book shows the progression from the raw materials needed to produce prepolymers to the production of prepolymers. This will include both the chemistry and the practical side of the production processes. 

Basic polyurethane chemistry was discovered by Otto Bayer in 1937, but polyurethane polymers were first developed as replacements for rubber at the start of World War II. Numerous applications followed including fibres, rigid and flexible foams, mouldings and elastomers (Brydson, 1999). The preparation of polyurethane polymers occurs via a reaction process intermediate between those of addition and condensation (Brydson, 1999). Like addition polymerization, there is no splitting off of small molecules, but the kinetics are otherwise similar to condensation polymerization. 

Head of the Division of Polymer Chemistry, National Chemical Laboratory, Pune, India Polyurea Polyurethane Polyurethane elastomers Polyurethane urea... 

We have prepared novel polyurethane elastomers with modified soft segment chemistry that has been designed to enhance stability. The new tliermoplastic polyurethanes are based on conventional diisocyanates and chain extenders, but contain macrodiols with a reduced number of ether linkages when compared with PTMO. As part of the development process, improved synthetic procedures involving condensation polymerization were devised (8,9) to prepare the macrodiols, poly(hexamethylene oxide) 1, poly(octamethylene oxide) 2, and poly(decamethylene oxide) 3. 

Baumann, G. F. (1969 ), Solid Polyurethane Elastomers, Wright, Haigh, and Hochland, Ltd. Bawn, C. E. H., ed. (1972), Macromolecular Science (MTP International Review of Science, Physical Chemistry Series One, Vol. 8), London, Butterworths, and Baltimore, Maryland, University Park Press. 

Modem chemistry has created a number of new mold-making materials with improved performance. These include organic resins for rigid molds as well as thermoplastic vinyl rubbers, polyurethane elastomers and, finally, RTV-2 silicone rubbers. The latter have become more and more used, in spite of their relatively high price, because they are the only materials that offer the ideal combination of properties essential for high-performance molding applications. 

A series of studies was also made by us, of the PUs cyclic stress-strain response. The range of structures achieved by us was widened by inclusion of DBDI, as a diisocyanate with a very strong tendency to packing due to its constitutional mobility. A systematic investigation (as shown in Table 4.5), was made of the effects of varying HS and SS chemistry, crosslinking and preparation procedures, on the hysteresis behaviour and Mullins effect of melt-cast polyurethane elastomers. The... 

Polyurethanes elastomers are a highly versatile class of materials in their own right. For their potential to be exploited more fully, a better understanding of their behaviour is still needed. Understanding the properties of the polyurethanes in terms of their chemistry and molecular architecture raises many new scientific challenges. 

Gunatillake, P. A., Martin, D. J., Meijs, G. F., McCarthy, S. J. Adhikari, R (2003) Designing biostable polyurethane elastomers for biomedical implants. Australian Journal of Chemistry, 56, 545-557. 

Marija Pergal, MSc, works at the Department for Polymeric Materials, Institute for Chemistry, Technology and Metallurgy since 2003 as Research Scientist. Since 2007 she is also Teaching Assistant for the course Chemistry of Macromolecules at Department of Chemistry, University of Belgrade. Her research interests are focused on synthesis and characterization of siloxane homopolymers and copolymers, especially thermoplastic elastomers based on poly(butylene terephthalate) and polyurethanes, as well as polyurethane networks based on hyperbranched polyester. In addition to physico-chemical, mechanical and surface properties of polymers, her particular interest is directed towards the study of biocompatibility of polymer materials. 

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