Polyurethane polymers description

Isocyanate chemistry is of itself a very complex field of chemistry, and even a brief description of the extent is outside the scope of this article. For a comprehensive description of isocyanate chemistry and its applications to polyurethane polymers, readers are directed to a handbook that is the standard in the industry [1]. A brief description follows for the purpose of introducing the role of isocyanates in polyurethane chemistry. 

This simple reaction is the bedrock of the polyurethane iadustry (see Urethane polymers). Detailed descriptions of the chemistry and process have been published (65—67). Certain carbamates are known to reversibly yield the isocyanate and polyol upon heating. This fact has been commercially used to synthesize a number of blocked isocyanates for elastomer and coating appHcations. 

For those familiar with polymer chemistry, polyurethane may be a confusing term. Unlike polyethylene, the polymerization product of ethylene, a polyurethane is not the result of the polymerization of urethane. To add to the confusion, a urethane is a specific chemical bond that comprises a very small percentage of the bonds of a polyurethane. Since we are interested in chemical and physical effects, polyether or polyester is a more descriptive term for the most common bond in a polyurethane. Despite this complication, it is instructive to begin by talking about the methane bond from which the polyurethane name is derived. The general structure or bond that forms the basis of this chemistry is the urethane linkage shown in Figure 2.1. 

Rigid foams are used for structural and insulation uses while the flexible materials are used for a vast variety of applications as seen in Figure 2.20. The versatility of polyurethane positions the product as unique in fire polymer world because of the breadth of applications. As we will show, small changes in chemistry can achieve a broad range of physical properties. This statement emphasizes the physical properties and serves as a testament, however, to the lack of chemical interest. It is supported by a description of the independent variables of density and stiffness and the range of products based on the primary attributes of polyurethanes. See Figure 2.21. 

The third approach to synthetic polymers is of somewhat less commercial importance. There is in fact no universally accepted description for the route but the terms rearrangement polymerisation and polyaddition are commonly used. In many respects this process is intermediate between addition and condensation polymerisations. As with the former technique there is no molecule split out but the kinetics are akin to the latter. A typical example is the preparation of polyurethanes by interaction of diols (di-alcohols, glycols) with di-isocyanates (Figure 2.7). 

Butanediol (1,4 BDO) is an intermediate used to produce several important petrochemical and polymer derivatives. One of the most visible and widely used polymers is spandex fiber (polyurethane fiber) however, many other high performance polymers and solvents are made from 1,4 BDO. A complete description of supply, demand, and uses for its derivatives is included in Chapter 6. The manufacture of 1,4 BDO by each of several alternative commercial routes are major users of hydrogen for hydrogenation. 

Although these definitions were perfectly adequate at the time, it soon became obvious that notable exceptions existed and that a fundamentally sounder classification should be based on a description of the chain-growth mechanism. It is preferable to replace the term condensation with step-growth or step-reaction. Reclassification as step-growth polymerization now logically includes polymers such as polyurethanes, which grow by a step-reaction mechanism without elimination of a small molecule. 

When the number of repeating units in a polymer chain is low, that is when the molecular weight of the polymer is low (2000-10000 g mol ), the polymer is defined as a resin, provided it possesses sufficient numbers of active sites in its structures for chemical cross-linking to occur. The resins can form three-dimensional network structures if sufficient external energy (heat/light/radiation) is applied, with or without the use of any other chemical(s) in their finished state. They are free flowing materials of low viscosity. Polyester resins, epoxy resins, and polyurethane resins are examples of this type of polymer. This book contains descriptions of the different types of resins derived from various vegetable oils. 

Estlander T, Kilpikari I, Eskolin E (1980) Permeability of polymer gloves and chemicals used in the manufacture of gloves (in Finnish). Suomen La arilehti (Finnish Med J) 35 800-803 Estlander T, Jolanki R, Kanerva L (1986) Dermatitis and urticaria from rubber and plastic gloves. Contact Dermatitis 14 20-25 Estlander T, Jolanki R, Kanerva L (1987) Contact urticaria from rubber gloves a detailed description of four cases. Acta Dermatol Venereol Suppl (Stockh) 134 98-102 Estlander T, Keskinen H, Jolanki R, Kanerva L (1992) Occupational dermatitis from exposure to polyurethane chemicals. Contact Dermatitis 27 161-165... 

Around 110 megatons (Mt) of CO2 are annually used in commercial synthesis processes, to produce urea, salicylic acid, cyclic carbonates, and polycarbonates. The largest use is for urea production, which reached around 90 Mt/yr in 1997. In addition to these applications, there are a number of promising reactions currently under study in various laboratories, reactions that differ in the extent to which CO2 is reduced during the chemical transformation. They include the synthesis of commodities and intermediates (acetic acid, methanol, carbonates, cyclic carbonates, and lactones), polymers (polyurethanes, polypyrones) and a variety of functionalized carboxylic acids (propenic acid, 3-hexen-l,6-dioic acid). A more detailed description can be found in the cited review. ... 

It is to be noted that not all polymers made by the condensation method form a condensate during the reaction. Polyurethanes which are formed by a reaction of isocyanates and alcohols are such an example. Also, ring opening polymerization reactions are considered to be of the addition type even though they form polymers which can also be formed by a condensation reaction, e.g., the polymerization of caprolactam to form nylon 6,6 (see Painter and Coleman, (1994)). As a result, most modem texts do not use the polymerization descriptions, condensation and addition. Rather, the terms step growth and chain are used in place of condensation and addition respectively. 

A detailed examination of the advantages and disadvantages of polymer recycling by considering several life cycle analysis case studies is given in [82]. Here, a short description of the relevant life cycle analysis of flexible polyurethane foam wastes is presented, with emphasis on the relation between the start and the end of the product s life, i.e., including process and product design. 

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