Polyurethane Family

Given the wide variety of chemical structures within the polyurethane family, it should come as no surprise that polymer scientists can tailor compositions and structures to meet a correspondingly broad range of end use requirements. In order to better understand the nature of these relationships, we have divided this section into subsections based on some of the more characteristic forms in which we encounter these materials. 

Some polymers can be used to produce foam possessing a wide range of properties. For example, polyurethane can be made hard or soft, flexible or rigid, at high or low densities. Polyurethane has an exceptional range of physical property variation and provides an unprecedented example to which many of the other cellular polymer test methods can be compared. Indeed, many of the methods used for the polyurethane family of polymers are eommon to the other polymeric foams. This subject is extensive, and a chapter such as this cannot hope to be exhaustive. However, it is hoped that most major physical property measurements are covered or at least guidance given to the reader as to where details can be obtained. 

Polyurethanes were invented in the 1930s and saw their first application during World War 11. Their excellent mechanical properties (a combination of toughness and flexibility), chemical stability, and processability quickly suggested numerous applications. Their application in medicine was spurred by an important paper on the use of one specific family of polyurethanes in the artificial heart. This polyurethane family, segmented block copolyurethaneureas, was first sold under... 

Thus it can be seen that the polyurethane family of polymers is really a family of related copolymers. By varying the type and size of the polymeric intermediates and of the distribution of the urethane, allophanate etc. links final polymers can be produced which show a very wide variation in properties. 

Polyurethane adhesives and sealants are part of the polyurethane family legacy that emerged in 1937 when Bayer et al. pioneered the polyaddition polymerisation... 

Increasing importance of other chemistries in the polyurethane family, such as polyureas and... 

According to Sika the most versatile and widely used sealants are those derived from the polyurethane family. A vast range of properties may be gained from these, thus offering the option of products tailor made for the different application requirements. 

Acetylene is condensed with carbonyl compounds to give a wide variety of products, some of which are the substrates for the preparation of families of derivatives. The most commercially significant reaction is the condensation of acetylene with formaldehyde. The reaction does not proceed well with base catalysis which works well with other carbonyl compounds and it was discovered by Reppe (33) that acetylene under pressure (304 kPa (3 atm), or above) reacts smoothly with formaldehyde at 100°C in the presence of a copper acetyUde complex catalyst. The reaction can be controlled to give either propargyl alcohol or butynediol (see Acetylene-DERIVED chemicals). 2-Butyne-l,4-diol, its hydroxyethyl ethers, and propargyl alcohol are used as corrosion inhibitors. 2,3-Dibromo-2-butene-l,4-diol is used as a flame retardant in polyurethane and other polymer systems (see Bromine compounds Elame retardants). 

The largest segment of the CASE family of polyurethanes are elastomers. Cast polyurethane elastomers reached a new dimension when high pressure impingement mixing led to reaction injection molding (RIM). This technology is used widely in the automotive industry, and reinforced versions (RRIM) and stmctural molded parts (SRIM) have been added in more recent years. 

To make clear how far we have come along this road, let us compute a specific fire. Consider an apartment house with various apartments opening onto a 44m (144.4 ft) long corridor, Figure 1. A fire occurs in a 4 x 5 x 2.4m (13x16x8 ft) room 30 meters (98.4 ft) from the open end of the corridor. A family, father, mother, young boy, and baby, are asleep in a suite of rooms at the closed end of the corridor. The room where the fire occurs contains a bed, polyurethane mattress, an upholstered polystyrene frame, polyurethane foam padding and fabric chair and a wooden dresser. 

Chemolysis certain polymer families such as polyurethane are chemically depolymer-ized. This is theoretically the best recycling solution if the performances of the original material are to be recovered and if the recyclate is used in the same application. This is, technically and economically, a difficult method that is industrialized in few cases. 

It is, of course, possible to prepare a molecule that has both polar and nonpolar characteristics. This is the basis of surfactant chemistry. Typically, a nonpolar molecule is modified by sulfonation. The well-known Pluronic family of surfactants is based on block polymerization of polypropylene oxide (the hydrophobe) and polyethylene oxide (the hydrophUe). It is conceptually possible to build a polyurethane 2005 by CRC Press LLC... 

POLYURETHANES. [CAS 9009-54-5]. These materials comprise a conglomerate family of polymers in which formation of tile urethane group... 

A family of elastomeric foams has been developed by Rand 129) for use as stress relief coatings on electronic components in encapsulated electronic assemblies. Polysulfide, silicone and polyurethane elastomers blended with glass and phenolic microspheres have been used to formulate syntactic foams (Fig. 10) These foams are used to minimize the stress caused by differential thermal expansion between the component and the encapsulant. 

Homogeneous ideal networks, also called closed networks, result from a single-step polymerization mechanism of a stoichiometric mixture of monomers, reacted to full conversion. Many amine-crosslinked epoxies of Tg < 200°C and polyurethanes obtained using a single isocyanate monomer and a single polyol belong to this family. 

This book is studying the castable family of polyurethanes. The cured polyurethane elastomer is made from three main ingredients that are detailed in Table 2.1. 

Polyurethanes (PU). The thermosetting type of this large family of polymers is mainly used as foam. A mixture of two components with a foaming agent forms a light, hard foam, which is a superior thermal insulator. 

Thermoplastic elastomers (TPE s) are characterized by the exceptional property that, without vulcanization, they behave as cross-linked rubbers. They are block-copolymers, in which blocks of the same nature assemble in hard domains, acting as cross-links between the rubbery parts of the chain. These hard domains lose their function when they reach their softening temperature, so that the material can then be processed as a thermoplast. One of the oldest member of the family of TPE s is SBS (styrene-butadiene-styrene block copolymer), but several other TPE s have been developed, i.a. on the basis of polyesters, polyurethanes and polyolefins. In their properties these polymers cover a broad range between conventional rubbers and soft thermoplastics. 

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