Thermoplastic Linear Urethane Elastomers

Completely linear urethane block copolymers are widely used as melt processing thermoplastics and as coatings and adhesives applied by both melt and solution techniques. In principle they form two classes  

Class 1. These are completely soluble in solvents, such as dimethyl-formamide (DMF), and possess no chemical crosslinks before or after processing. 

Class 2. These materials possess no crosslinks before processing but if given a heated post-cure will develop a lightly crosslinked structure. After crosslinking they are insoluble in solvents. 

Class 1 are the predominantly used class of polyurethanes and can be processed using traditional thermoplastic melt techniques. Class 2 represents a small specialist group used where higher temperature, lower compression set and environmental stress cracking resistance is required. 

The synthesis principle used to prepare thermoplastic urethane elastomers is outlined in Fig. 2.4. 

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Published information on urethane polymerization detail largely concerns thermoset urethane elastomers systems.4 13 In particular, the work of Macosko et. al. is called to attention. The present paper supplements this literature with information on the full course of linear thermoplastic urethane elastomer formation conducted under random melt polymerization conditions in a slightly modified Brabender PlastiCorder reactor. Viscosity and temperature variations with time were continuously recorded and the effects of several relevant polymerization variables - temperature, composition, catalyst, stabilizer, macroglycol acid number, shortstop - are reported. The paper will also be seen to provide additional insight into the nature and behavior of thermoplastic polyurethane elastomers. 

Chem. Descrip. Linear poly (1,4-butanediol-1,6-hexanediol adipate) Uses PU intermediate for very flexible thermoplastic urethanes, urethane coatings, and urethane elastomers... 

Desmocoll 176, 400 and 420 are primarily linear thermoplastic polyurethane elastomer resins of medium, medium-high and high crystallization rates, respectively. They are supplied as small, light brown, talc-covered, pieces. The polymers have a density of 1 2-1-23 g cm . This density, and their stabilization by the hydrolysis stabilizer Staboxal PCD, imply that they are poly(ester-urethanes). They show outstanding adhesion to numerous materials including plastics, rubber, leather, fabrics, wood, metals, etc. 

Segmented polyurethanes (PUs) are typical representatives of linear block copolymers of the type (A-B)jj and an important class of thermoplastic elastomers. They are composed of short alternating blocks of soft (SS) and hard segments (HS). The SS impart elastomeric character to the copolymer, whereas the HS form a solid phase (HS microdomains) through intermolecular association and impart dimensional stability to the array of macromolecules. Low molecular mass polyethers and polyesters are typically used as SS, while HS normally consist of an aromatic diisocyanate that has been chain extended with a low molecular weight diol or diamine to form an oligomeric aromatic urethane or urethane urea segment [1-3]. 

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