Properties polyurethanes

Polymerization of the oxiranes is typically propagated from a starter molecule that is chosen to define the functionality if) of the final polyol. The functionality and the molecular weight of polyols are the main design features that define the polyurethane properties in the end-use applications. Additionally, the balance of EO and PO in the polyether polyols, mainly for flexible foam polyols, is tailored to enhance the compatibility of formulations and the processability of the foam products. The exact composition of the polyols defines the crucial performance features of the final polyurethane product. Even seemingly small differences in polyol composition can result in changes to polyol processabihty and polyurethane performance. This becomes a crucial issue when replacing conventional petrochemical polyols with polyols from different feedstocks. To demonstrate the sensitivity of commercial formulations to changes in feedstocks, a simple example is offered below. 

A mode of wear is microcutting, where a sharp edge will cut through the surface. The general mechanism is shown in Figure 7.16. Polyurethane under tension will wear at a greater rate than one that is under slight compression. This is similar to other polyurethane properties such as cut and ozone resistance. 

Hard segment One of the two phases that make up polyurethane. The hard segment is made from isocyanates and chain extenders. The hard segment controls many of the polyurethane properties such as tensile, tear strength, hardness, compression set, abrasion/erosion resistance, and thermal stability. 

As may be expected, many factors affect polyurethane properties which are important in practical apphcations. For example, films, adhesives, and foamed resins can be obtained by suitable formulation, particularly by variation in the nature of the polyol (72). 

Although there is considerable published literature on the relation of polyurethane properties to their chemical and physical structures, considerably less has appeared concerning the detailed nature of urethane polymerization. The thermoset nature of the classical polyurethane systems, which has provided fewer opportunities and thus less scientific interest for the study of the intermediate stages and course of urethane polymerization, likely helps account for this. 

In most of our studies, modification of the synthetic route was limited to only one variable, the chain length of the polyether component. The same molar ratio of polyether/chain extender disocyanate (MDI) and chain extender (diethlene glycol) were used. The molecular weight of the polyether component of J-20, J-9 and J-6 was 2,000, 1,000 and 600 respectively. A wide range of properties was obtained from this series of polyurethanes. Properties intermediate between J-20 and J-9 were also obtained by... 

Relationships Between the Oligo-Polyol Structure and Polyurethane Properties... 

The structure - property relationships in polyurethanes (PU) have been excellently presented in the general monographs on PU [1-11]. As a consequence, this chapter will not be very long and it will present only the specific general effects of the oligo-polyol s structure on the resulting polyurethane properties. 

The MW of oligo-polyols, is usually in the range of 400 to 6500 daltons, and it has an important effect on the polyurethane properties. Thus, if the polyol has a low MW, a hard polyurethane will result and if the polyol has a high MW, it creates elastic, flexible polyurethanes. Intermediate MW lead to semirigid or semiflexible structures [2]. 

The present monograph is dedicated to these very important raw materials used to build the polyurethane polymeric architecture and covers chemistry and technology of oligomeric polyol fabrication, properties of these hydroxyl terminated oligomers and the effects of the oligomeric polyol structure on the resulting polyurethane properties. 

Impact of Composition on Polyurethane Properties 126 7.6 Polyurethane Applications 137... 

THE MECHANISM OF THE SPECIFIC ACTION OF PLASTICIZERS AND ITS EFFECT ON POLYURETHANES PROPERTIES... 

Figure 8.11 Variation of cast polyurethanes properties as a function of hardness...

Polyurethanes Properties vary from those of an elastomer to those of hard, rigid cross-linked polymers with mechanical properties showing no reduction after an exposure to 1000 Mrad. (General radiation resistance excellent.)... 

PROPERTIES OF DIISOCYANATE CROSSLINKED POLYURETHANES Properties of Urepan 600 compounds... 

Kr61, P. Synthesis methods, chemical structures and phase structures of linear polyurethanes. Properties and apphcations of linear polyurethanes in polyurethane elastomers, copolymers and ionomers. Progress in Materials Science, 2007,52, 915-1015. 

P. Alves, P. Ferreira, M.H. Gil, Biomedical Polyurethane-Based Materials, in Polyurethane Properties, Structure and Applications, Nova Publishers, New York, 2012. ISBN ... 

Possibly another polyester polyol could be used in place of this specific polyester however, some of the polyurethane properties might be different. 

Other types of polyols with ether linkages can be used however, the polyurethane properties might be changed. 

Sonnenschein M F, Rondan N, Wendt B and Cox J M (2004) Synthesis of transparent thermoplastic polyurethane elastomers, J Polym Sci Part A Polym Chem 42 271-278. Sonnenschein M F, Lysenko Z, Brune D A, Wendt B L and Schrock A K (2005) Enhancing polyurethane properties via soft segment crystallization. Polymer 46 10158-10166. 

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